True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata

Lecture Notes in Geoinformation and Cartography Series Editors: William Cartwright, Georg Gartner, Liqiu Meng, Michael ...

Author: Manfred Buchroithner

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Lecture Notes in Geoinformation and Cartography Series Editors: William Cartwright, Georg Gartner, Liqiu Meng, Michael P. Peterson

Manfred Buchroithner Editor

True-3D in Cartography Autostereoscopic and Solid Visualisation of Geodata

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Editor Manfred Buchroithner TU Dresden Helmholtzstrasse 10 01062 Dresden Germany [email protected]

ISSN 1863-2246 e-ISSN 1863-2351 ISBN 978-3-642-12271-2 e-ISBN 978-3-642-12272-9 DOI 10.1007/978-3-642-12272-9 Springer Heidelberg Dordrecht London New York Library of Congress Control Number: 2011934867 c Springer-Verlag Berlin Heidelberg 2012 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

Preface

Over the past fifteen years the city of Dresden in Germany has been gaining international reputation in the autostereoscopic depiction of geodata. Hardcopy and softcopy displays are currently being developed and produced by the Dresden University of Technology and three other Dresdenbased commercial companies, all spin-offs of the university. This recent increase in interest and the principally intuitive appeal of “True-3D” in geodata presentation fuelled our motivation to compile a textbook about the present technical status and recent innovative developments. As a primary step towards attaining this goal a first international symposium was organized in close cooperation with the Executive Committee of the International Cartographic Association (ICA), with several of its Commissions as well as with the support of SPIE Europe and on behalf of the German Cartographic Society (DGfK). The symposium covered almost all aspects of autostereoscopic representations of both topographic and thematic geodata, be they haptic or not, and took place in Dresden between 24th and 28th August 2009. Displays for large audiences were under discussion along with special single-user applications, and well-established technologies contrasted strongly with cutting-edge developments. This attracted experts from the international cartographic “true-3D community” who exchanged opinions and knowledge about the state-of-the-art in various fields. Most of the information conveyed during this international symposium has been compiled to form the present volume. Although being far from all-embracing, it represents a first “anthology” treating the rapidly evolving complex field of “True-3D in Cartography”. The contributions contained in this book were reviewed at least twice by an international group of scientists (in alphabetical order): Manfred F. Buchroithner (Dresden, Germany), Arzu Coltekin (Zurich, Switzerland), Harold Moellering (Columbus, Ohio/USA), and Wolf-Dieter Rase (Bonn, Germany). As editor, I am very thankful for the critical remarks of my colleagues with regard to both the articles’ contents and the authors’ phrasing.

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The production of this book would not have been possible without the professional and formidable efforts of Steffi Sharma, Jana Simmert, Ulrike Schinke and Rebecca Dittmann. I also extend my thanks and gratitude to them. Manfred F. Buchroithner

List of Contributors

Armstrong, Robert W. NERC, British Geological Survey Kingsley Dunham Centre, Keyworth, NG12 5GG, Nottingham United Kingdom Ascencio Escamilla, Maria Guadalupe CUCEI, Universidad de Guadalajara Blvd. Marcelino García Barragán #1421, JAL 44430 Guadalajara Mexico Bektaş, Kenan Department of Geography, University of Zurich – Irchel Winterthurerstr. 190, CH-8057 Zurich Switzerland Boulos, Maged N. Kamel Faculty of Health, University of Plymouth Drake Circus, Plymouth, Devon PL4 8AA UK Bruhm, Katharina Institute for Cartography, Dresden University of Technology Helmholtzstr. 10, 01062 Dresden Germany Buchroithner, Manfred F. Institute for Cartography, Dresden University of Technology Helmholtzstr. 10, 01062 Dresden Germany Büyükbayrak, Hakan General Command of Mapping Tip Fakültesi Caddesi, 06100 Ankara Turkey

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Çöltekin, Arzu Department of Geography, University of Zurich – Irchel Winterthurerstr. 190, CH-8057 Zurich Switzerland Dalkiran, H. Polat General Command of Mapping Tip Fakültesi Caddesi, 06100 Ankara Turkey Doležal, Jan Department of Geoinformatics, Palacký University Olomouc tř. Svobody 26, 771 46 Olomouc Czech Republic Döllner, Jürgen Hasso-Plattner-Institut, University Potsdam Postfach 900460, 14440 Potsdam Germany Dolz, Wolfram State Art Collections Dresden, Mathematical-Physical Salon, Zwinger Palace Theaterplatz 1, 01067 Dresden Germany Eisfelder, Christina German Remote Sensing Data Center (DFD), German Aerospace Center (DLR) Oberpfaffenhofen Münchner Straße 20, 82234 Wessling Germany El Nabbout, Khaled Chair of the Geosciences Department, European Arabic Engineers Union Am Kuesterland 18, 44892 Bochum Germany Finková, Dita Institute of Special Education Studies, University Olomouc Žižkovo nám. 1, 771 00 Olomouc Czech Republic


Fritsche, Niels-Christian Institute of Foundations of Design and Architectural Delineation, Dresden University of Technology 01062 Dresden Germany Gede, Mátyás Department of Cartography and Geoinformatics, Eötvös Loránd University Egyetem tér 1-3., 1053 Budapest Hungary Gindele, Matthias ACADIS GmbH Boelckestrasse 26, 55252 Wiesbaden Germany Götzelmann, Timo Department of Research and Development, PreDevelopment, NAVIGON AG Berliner Platz 11, 97070 Hamburg Germany Gründemann, Thomas mbmSystems GmbH Lingnerallee 3, 01069 Dresden Germany Habermann, Klaus mbmSystems GmbH Lingnerallee 3, 01069 Dresden Germany Hahmann, Thomas German Remote Sensing Data Center (DFD), German Aerospace Center (DLR) Oberpfaffenhofen Münchner Straße 20, 82234 Wessling Germany Hetze, Bernd Center of Information Services and High Performance Computing, Dresden University of Technology 01062 Dresden Germany

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Jobst, Markus Hasso-Plattner-Institut, University Potsdam Postfach 900460, 14440 Potsdam Germany Katzer, Jochen Department of Research and Development, PreDevelopment, NAVIGON AG Berliner Platz 11, 97070 Hamburg Germany Knust, Claudia Institute for Cartography, Dresden University of Technology 01062 Dresden Germany Koch, Wolf Günther Institute for Cartography, Dresden University of Technology 01062 Dresden Germany Kolecka, Natalia Institute of Geography and Spatial Management, Jagiellonian University ul. Gołębia 24, 31-007 Krakow Poland Kozáková, Magdaléna Department of Geoinformatics, Palacký University Olomouc tř. Svobody 26, 771 46 Olomouc Czech Republic Ledesma Tello, Ismael Luis CGTI, Universidad de Guadalajara Juárez #976, JAL 44100 Guadalajara Mexico Lorenz, Haik Hasso-Plattner-Institut, University Potsdam Postfach 900460, 14440 Potsdam Germany Ludíková, Libuše Institute of Special Education Studies, University Olomouc Žižkovo nám. 1, 771 00 Olomouc Czech Republic

List of Contributers

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Mahmud, Ahmad Rodzi Department of Civil Engineering, Universiti Putra Malaysia 43400 UPM Serdang, Selangor Malaysia Mair, Toni Geomodelia, Landscape relief models studio Rainstrasse 24, 6314 Unteraegeri Switzerland Márquez Azúa, Bertha DGOT, Universidad de Guadalajara Guanajuato #1045, JAL 44260 Guadalajara Mexico Menounos, Brian Natural Resources and Environmental Studies Institute, University of Northern British Columbia 3333 University Way, V2N 4Z9 Prince George Canada Moellering, Harold Department of Geography, Ohio State University Enarson Hall 154 W 12th Avenue, 43210 Columbus USA Nausner, Ben Department of Geography and Regional Research, University of Vienna Universitaetstr 7, 1010 Wien Austria Němcová, Zuzana Department of Geoinformatics, Palacký University Olomouc tř. Svobody 26, 771 46 Olomouc Czech Republic Oksanen, Juha Department of Geoinformatics and Cartography, Finnish Geodetic Institute P.O. Box 15, FIN-02431 Masala Finland Özağaç, Servet Head of Relief Map Section, General Command of Mapping Tip Fakültesi Caddesi, 06100 Ankara Turkey

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Pradhan, Biswajeet Institute of Cartography, Dresden University of Technology 01062 Dresden Germany Rase, Wolf-Dieter Federal Office for Building and Regional Planning Deichmanns Aue 31-37, 53179 Bonn Germany Regec, Vojtěch Institute of Special Education Studies, University Olomouc Žižkovo nám. 1, 771 00 Olomouc Czech Republic Riedl, Andreas Department of Geography and Regional Research, University of Vienna Universitaetsstrasse 7, 1010 Wien Austria Robinson, Larry R. Geospatial Sciences and Technologies Branch, USGS-BRD-Upper Midwest Environmental Sciences Center 2630 Fanta Reed Road, La Crosse, Wisconsin 54603 USA Růžičková, Veronika Institute of Special Education Studies, University Olomouc Žižkovo nám. 1, 771 00 Olomouc Czech Republic Ruzinoor, Che Mat Department of Biological & Agricultural Engineering, Universiti Putra Malaysia 43400 UPM, Serdang, Selangor Darul Ehsan Malaysia Sanchez, Conrado Sigrid S.L. Ronda de Poniente n° 3, 28760 Tres Cantos (Madrid) Spain Sánchez, Javier González Tecnológico de Monterrey, Campus Guadalajara General Ramón Corona #2514, JAL 45201 Zapopan Mexico

List of Contributers

Sarjakoski, L. Tiina Department of Geoinformatics and Cartography, Finnish Geodetic Institute P.O. Box 15, 02431 Masala Finland Sarjakoski, Tapani Department of Geoinformatics and Cartography, Finnish Geodetic Institute P.O. Box 15, 02431 Masala Finland Schwarzbach, Friederike Department of Geoinformatics and Cartography, Finnish Geodetic Institute P.O. Box 15, 02431 Masala Finland Schwarzbach, Friederike Institute for Cartography, Dresden University of Technology 01062 Dresden Germany Shariff, Abdul Rashid Mohamed Department of Biological & Agricultural Engineering, Universiti Putra Malaysia 43400 UPM Serdang, Selangor Malaysia Stendel, Dirk ILaUP, Technische Universität Berlin Straße des 17. Juni 145, 10623 Berlin Germany Straumann, Ralph K. Department of Geography, University of Zurich – Irchel Winterthurerstr. 190, 8057 Zurich Switzerland Suter, Martin ESRI Schweiz AG Josefstrasse 218, 8005 Zurich Switzerland

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Trapp, Matthias Hasso-Plattner-Institut, University Potsdam Postfach 900460, 14440 Potsdam Germany Ungvári, Zsuzsanna Department of Cartography and Geoinformatics, Eötvös Loránd University Egyetem tér 1-3., 1053 Budapest Hungary Vondráková, Alena Department of Geoinformatics, Palacký University Olomouc tř. Svobody 26, 771 46 Olomouc Czech Republic Voženílek, Vít, Prof. Department of Geoinformatics, Palacký University Olomouc tř. Svobody 26, 771 46 Olomouc Czech Republic Weckman, Suvi Department of Geoinformatics and Cartography, Finnish Geodetic Institute P.O. Box 15, 02431 Masala Finland Weiss, Gunter, Prof. Institute of Geometry, Technische Universität Dresden 01062 Dresden Germany Wheate, Roger Natural Resources and Environmental Studies Institute, University of Northern British Columbia 3333 University Way, V2N 4Z9 Prince George Canada

Table of Contents

Preface

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List of Contributors .............................................................vii Introduction Perspectives on 3-D Visualization of Spatial Geodata and Future Prospects Moellering, H. ........................................................................................... 1

Section 1: Data and Techniques for True 3D Visualization How true is true-3D? – Geometry between Single Image Stereograms and Lenticular Foil Displays Weiss, G. and Buchroithner, M. F. .......................................................... 23 Survey of True 3D and Raster Level of Detail Support in GIS Software ................................................................................................. 43 Bektaş, K., Çöltekin, A. and Straumann, R. K. Think Differently: a New Method to Create Lenticular- and Integral-Pictures Stendel, D. ............................................................................................... 67 Truly modelling reality…? – Let’s improve our cognitive maps with a bastard mix of algorithms to “undo” pictures, isometric mapping, high-density diagrams and comic culture as integral sign posts for software development in cartography Fritsche, N. -C. ....................................................................................... 83

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Section 2: Planar Stereoscopic Hardcopies and Screens Autostereoscopic Maps on the Basis of Lenticular Foils Gründemann, T. and Habermann, K. ...................................................... 97 True-3D Visualization of Glacier Retreat in the Dachstein Massif, Austria: Hard- and Softcopy Displays Bruhm, K., Buchroithner, M. F., Hetze, B. and Gindele, M. ................. 105

Section 3: Physical Terrain Models Creating Physical 3D Maps Using Rapid Prototyping Techniques Rase, W. -D. .......................................................................................... 119

Section 4: Tactile Maps State of the Art of Tactile Maps for Visually Impaired People Koch, W. G. ........................................................................................... 137 Hypsometry in Tactile Maps Voženílek, V., Růžičková, V., Finková, D., Ludíková, L., Němcová, Z., Doležal, J., Vondráková, A., Kozáková, M. and Regec, V. ................... 153 Physical 3D models from LIDAR data as tactile maps for visually impaired persons Schwarzbach, F., Sarjakoski, T., Oksanen, J., Sarjakoski, L. T. and Weckman, S. .......................................................................................... 169

Section 5: Globes Blurring Boundaries Between Real and Digital/Virtual Globes – Creating virtual globes from real ones and vice versa Gede, M. and Ungvári, Z. ..................................................................... 187 The Digital True-3D Globe from Willem Janszoon Blaeu Knust, C., Buchroithner, M. F. and Dolz, W. ........................................ 199

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State-of-the-art of Tactile Hyperglobes Riedl, A. ................................................................................................. 215

Section 6: True 3D in Geophysics and Geology Explanation of the BGS Subsurface Viewer Armstrong, R. W. ................................................................................... 229 Three-Dimensional Visualisation of the Tectonic movement over Mexico by means of the Global Positioning System (GPS) measurements Azúa, B. M., Tello, I. L. L., Sánchez, J. G. and Escamilla, M. G. A. ........................................................................ 239

Section 7: Virtual Urban and Rural Landscape Visualization Terrestrial Laser Scan Application in Urban Planning El Nabbout, K. ....................................................................................... 259 3D Terrain Visualisation for GIS: A Comparison of Different Techniques Ruzínoor, C. M., Shariff, A. R. M., Mahmud, A. R. and Pradhan, B. .... 265

Section 8: Non-Planar Optical Projections Cartographic Representation of Dresden’s Historical Development by Projecting a Movie onto a Solid Terrain Model Hahmann, T., Eisfelder, C. and Buchroithner, M. F. ............................ 281 Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging Trapp, M., Lorenz, H., Jobst, M. and Döllner, J. .................................. 297

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Section 9: Topographing and Thematic Geovisualization Go True 3D 3D Representation of Retreating Glaciers: Anaglyphs and the Geowall Wheate, R. and Menounos, B. ............................................................... 315 High-resolution mapping and visualization of a climbing wall Kolecka, N. ............................................................................................ 323 TOPGIS - swisstopo’s Production System for 3D Topographic Databases Suter, M. ................................................................................................ 339 Temple complex ‘Virtual Nako’ – 3D Visualisation of cultural heritage in Google Earth Nausner, B. ............................................................................................ 349 Challenges and Perspectives for True–3D in Car Navigation Götzelmann, T. and Katzer, J. ............................................................... 357 Holographic Relief Map Production by Using Topographic Line Maps Dalkiran, H. P., Özağaç, S. and Büyükbayrak, H. ............................... 367

Section 10: 3D Geodata in the Web Stereoscopic 3-D solutions for online maps and virtual globes Buchroithner, M. F., Boulos, M. N. K. and Robinson, L. R. ................. 391

Section 11: Special Contributions The Landscape Relief Model - An anachronism or still a useful object for contemplating the landscape Mair, T. ................................................................................................. 415 StereoWebMap, A Real Stereoscopic Map Server for the Internet Sanchez, C. ............................................................................................ 435

Appendix.............................................................................447

Introduction

Perspectives on 3-D Visualization of Spatial Geodata and Future Prospects Moellering, H.

Perspectives on 3-D Visualization of Spatial Geodata and Future Prospects

Harold Moellering Department of Geography, Ohio State University, Columbus, Ohio, U.S.A.

Abstract For more than a century spatial scientists have sought to mathematically describe, illuminate, and visualize various forms of spatial surfaces, and other 3-D and higher dimensional spatial data. In the early years these were mostly physical terrain surfaces illustrated under the rubric of hill shading. In the first half of the 20th century rapid developments in 3-D visualization occurred largely in air photo and analogue photogrammetry. Beginning in the 1960s it became feasible to implement quantitative formulations in computing machines. This provided the opportunity to operationalize the mathematical theory in a digital virtual environment that was much more flexible than before. At about that time the use of homogeneous coordinate transformations provided a major breakthrough for digital 3-D object visualization. The involvement of interactive control and visualization techniques soon followed. Spatial surfaces, and especially topographic surfaces, were among the more popular objects. Since that time the theory of spatial surfaces and objects, spatial data structure designs, and the technology of display hardware have continued to develop and enhance the 3-D spatial visualization processes. This presentation will reflect on these conceptual and technical developments in spatial 3-D visualization from the perspective of four decades of involvement in the field. Comments and suggestions will be offered for suggestions of future developments.

M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_1, © Springer-Verlag Berlin Heidelberg 2012

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Keywords: Analytical Cartography, 3-D Stereoscopic Vision, Lenticular Vision, Virtual Maps, Perceptual Color Spaces, History of Visualization.

1 Introduction Today a wide range of individuals – also outside the field of cartography proper - is working with cartographic and spatial visualization, and with the hardware technology of 3-D displays. Many of them are using these concepts and technologies in interesting and effective ways. The present paper strives to present some historical background coming initially from the field of cartography and then from Analytical Cartography, and then later from some of the more scientific and technical topics that will provide more insight and enrich the discussion. It focuses on some broader spatial visualization topics, outside of the excellent visualization research conducted by Prof. Buchroithner and colleagues that will be discussed in individual papers in this volume. The article has a North American perspective. Much of the analytical theory is discussed by Harold Moellering (2000) in a review of the concepts in Analytical Cartography.

2 A look at some history of analytical visualization One can begin with the traditional hard copy map used over more than 3,000 years of human history. These 2-D hard copy maps served civilization well through the centuries for mapping and navigation purposes. Well known examples are Babylonian clay tablets, Egyptian maps on papyrus, Chinese imperial maps, down through the ages to European portolan charts that were used for navigation at the beginning of the Age of Discovery. One exotic example is the 2 1/2-D wood navigation models made by the Polynesian Islanders for sailing across the Pacific Ocean. Beginning in the 19th Century, one began to see the rise of Analytical Visualization where one began to use mathematical concepts to understand spatial surfaces and visualize them. One of the earlier was Cayley (1859) where he picked up on some of the concepts of continuous surfaces from mathematics. He also began to look at the critical points and lines on a surface where the mathematical derivatives change, and explore how those relate to surface contours and slope lines. Now spatial surfaces could be conceptualized analytically beyond just description.


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A couple of decades later, Wiechel (1878) began to use the concepts from what we now call the Cosine Law to calculate the illumination of a light source at a point on a topographic surface as shown in Fig. 1. This was a cumbersome effort because the angle between the light ray and the normal to the slope had to be derived indirectly with equations as shown in Fig. 2. This calculation using the normal to the slope, vertical of the topographic datum, azimuth to the light ray and azimuth to the surface normal is still used today in such computations. The irony is that at the time one could only make individual illumination calculations for individual points on a surface. It is only with a computer more half a century later did such calculations and surface illuminations become practical in the spatial sciences.

Fig. 1. Wiechel Aalytical Point Illumination 1878 (after Webster)

Fig. 2. Wiechel Illumination on a Surface (1878)

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Beginning in the 1950s one began to see the rise of computer technology in a systematic way that begins to provide digital approaches to spatial visualization. This provided the beginnings of spatial data base files, and the development of new hard copy technologies. Later as the 1970s dawned did one see the development of several key conceptual and technical innovations in computer graphics which greatly benefited spatial visualization. They were: 1) Homogeneous Coordinate axes, which provided for more robust calculations of nearly parallel coordinate axes, 2) Homogeneous Matrix Transformations, which provided 3-D "straight space" orthogonal axis transformations such as translation, rotation, scaling, and perspective, 3)More effective and efficient visible surface algorithms based on the "straight space" coordinate axes. These led to many new strategies in spatial visualization. Also in the 1970s one began to see a host of conceptual innovations in spatial visualization that benefited from the earlier innovations in computer and computer graphics concepts and technologies. Examples include: x x x x x x x x

Effective Square Cell Structures Raster-Vector Conversions Topological Spatial Data Structures Invention of the Triangulated Irregular Network - TIN Model Development of the Warntz Network on a Surface Development of "Pfaltz" surface networks Creative uses of reorienting sun angle on a surface Topological Surface Generalization.

There is a rich literature on these and many other conceptual innovations in spatial visualization during this period. One further example is that by Horn (1982) which reviews the concepts of computer graphics and shading, and integrates that with existing concepts of Analytical Hill Shading from the spatial visualization literature. He managed to bring the concepts from these different fields together into one publication.

3 Real and virtual maps and their transformations One can now turn to the rich variety of 2-D and 3-D maps that have been developed in spatial visualization. They range from the lowly topographic map to the sophisticated 3-D lenticular displays. Some are hard copy real maps, and some are various forms of virtual maps. Fig. 3 shows a selected list of such products. The primary question is how can one understand them on a conceptual basis?


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Fig. 3. Many Kinds of Map Products

One approach is to look at the two fundamental conceptual characteristics of such a display, and then to classify them. The first characteristic is whether the product is hard copy or not. The second is whether the product is directly visible as a spatial/cartographic image, or not. From there on can construct a four class table of Real and Virtual Maps as shown in Fig. 4. This particular Table of Real and Virtual Maps contains 3-D examples that are in harmony with the theme of the conference. Now one can better understand the kind of spatial product and its characteristics that one is working with. This fourfold classification helps one to more systematically understand these products and how they relate to each other.

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Fig. 4. The Scientific Definition of 3-D Real and Virtual Maps

When one is working with such spatial visualization products, one typically begins with spatial data, a Virtual type 3 product and transform it into a product that is visible, a Real Map if it is hard copy, and a Type 1 virtual display if it is not hard copy. It turns out that when working with spatial data and generating spatial displays one typically makes many of these kinds of Real/Virtual map transformations in the process. Fig. 5 shows the 16 possible Real/Virtual map transformations that are possible. If one considers these 16 transformations carefully, it becomes clear that they define all of the processing steps one could make while processing spatial data.

Fig. 5. 16 Transformations Between Real and Virtual Maps Defines all Operations in Spatial Data Sciences

One straightforward example shown in Fig. 6 is a Real Time Interactive Spatial Analysis System at a very general level. Most spatial data display systems are configured like this at this level of generality. One could then go in and define these processes at a much greater level of detail in terms of the Real/Virtual transformations taking place in such a system. This means that any kind of spatial data processing or display system can be conceptually understood as working with a host of sequential Real/Virtual map transformations as it operates. One can also use such transformations to help design such a system and the functionalities it contains.


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Fig. 6. Real Time Spatial Analysis and Display System Conceptualized With Real and Virtual Map Transformations

4 Deep and Surface Spatial Structure While examining the spatial characteristics of spatial data, one can also consider the concept of Deep Structure. Nyerges (1980) adapted the concept of deep structure over from the discipline of structural linguistics to serve this purpose with spatial data. Fig. 7 illustrates the concept of Deep and Surface spatial structure in the spatial sciences. Here Surface Structure is spatial data that is in spatial products that are visible to the observer. These are Real Maps and Virtual Map Type 1.

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Fig. 7. Representation of Deep and Surface Spatial Structure

Then Deep Structure is the characteristic of spatial data that is not directly visible, say data deeper in a spatial data structure in a system. Virtual Maps Type 3 fall into this category. Please also refer to Fig. 4. In an interactive spatial data processing system, the computational processing of the data takes place in the deep structure level, and then when it is visualized, it emerges into the surface structure. Spatial metadata is a good example of Deep Structure information about a spatial feature. The concept of Deep and Surface Spatial structure helps the researcher to more fully understand the characteristics of the spatial data with which one is dealing. The concepts of Deep and Surface Structure and Real/Virtual Maps complement each other conceptually and scientifically to yield a better understanding of the spatial data one is processing and visualizing.

5 Nyerges Spatial Data Levels A third major concept that helps us understand the concepts of spatial data more completely is that of Nyerges Data Levels (1980). One begins with:


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x Real World Entities 1. Data Reality - Geographic entities in the Real World; 2. Information Structure - A formal model of geographic entities and their relationship in the Real World. Real World Entities are things that exist in the real world such as buildings, roads and lakes. The Information Structure contains the spatial relationships between these various Real World Entities. x Spatial Object Model 3. Canonical Model - A formal model of the spatial data objects in the deep structure; 4. Spatial Data Structure - An operational spatial data model used for spatial analysis and visualization. The Canonical Model takes the same relationships from the Information Structure and now relates those relationships to the defined spatial data objects. These are then organized into the Spatial Data Structure to produce a working spatial database. x System Hardware & Architecture 5. Storage Structure - The file structures of how the spatial data structures are stored in the computer system. 6. Machine Encoding - A machine representation of the file structures in the computer system hardware, e.g. bits and bytes. Most spatial scientists work with the first four levels of data, while only computer specialists would deal with levels 5 and 6. This conceptual organization of data levels is distinctive in that it separates the spatial relationships into two levels: the Information Structure which points up to the Real World entities, and the Canonical Model which deals with the spatial objects such as nodes, links and polygons. Many approaches lump those two levels together, but in the spatial sciences it is very helpful to specify them separately as Nyerges has done. This improves the conceptual understanding of how one is treating the spatial data involved in the system.

6 Early 3-D digital stereoscopic visualization Stereoscopic visualization has been a part of civilization for millennia as ordinary human 3-D analogue vision. In the last few decades mechanical analogue approaches to stereoscopic vision has been developed with the use of analogue stereo pairs in air photo analysis. This was enhanced with the later development of analogue photogrammetric instruments. However,

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digital stereoscopic display has been more recent, coming in during the 1980s. Fig. 8 shows an early configuration with a Tektronix 4337 3-D Stereoscopic workstation in 1988. It featured radial polarization in the display screen itself that had a 120 Left/Right noninterlaced refresh rate of 120 Hz. Tektronix holds the patents on this development. The workstation also used a perceptual colour space of either HLS or TekHVC. Tektronix put their HLS colour space development into the public domain, while it retains the patent on the TekHVC Colour space. Everything was digitally controlled, and the user could manage the relevant display parameters. Fig. 9 shows a crowd watching Prof. Moellering presenting this paper at AutoCarto 9 in 1989. This example illustrates that digital stereoscopic display has been a going concern for more than 20 years. Tektronix was a true pioneer in this area. Newer developments in stereoscopic display, as will be discussed in this Dresden meeting, are showing continuing improvements to the technology.

Fig. 8. Stereoscopic Viewing Using Left and Right Images (Figure Copyright Tektronix Inc. 1988)


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Fig. 9. Watching Moellering 3-D Presentation at Auto-Carto 9, 1989

7 Some examples of analytical visualization The strategies of Analytical Visualization shown here involve taking a spatial surface, here topography, and then doing something analytical with processing the data, or perhaps combining data overlays in the colour space to produce a resulting display. Fig. 10 shows a basic 4 pane screen for 2-D surface data processing. The HLS colour space is used in these examples. The Upper right pane is gray shaded topography illuminated from 315 degrees. Below it is a pane of LANDSAT infrared imagery shaded in green according to the distribution shown in the pane on the upper left. These two panes can then be combined in the colour HLS space to create the resulting visualization. Many other analytical approaches are possible, such as shading the surface slope in continuing gradations of a hue, or taking the Z data distribution and, where appropriate, applying different hues left and right away from the central peak of the Z distribution. This analytical shading can then be applied to a 3-D surface as shown in Fig. 11. These sorts of analytical strategies can be developed to enhance visualization of 3-D surfaces in addition to the 3-D geometry and

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stereopsis. So the analytical work provides an additional bit of scientific analysis that can be added to the 3-D visualization itself.

Fig. 10. Analytical Visualisation-4 Pane Display


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Fig. 11. Large 3D surface demonstration (colour version on CD-ROM)

8 Somme comments about colour spaces One can discuss the kinds of colour spaces that are used with these kinds of 3-D visualizations. Most basic and typical of most applications is the use of the RGB cubic colour space where the Red, Green, and Blue colour axes are orthogonal to each other. This is the standard colour model used for computer display hardware. It is the way that the display hardware generates the colours displayed. However, it is well known that this is not the way people perceptually see colour. The three colour axes associated with the way people perceive colour are: Hue - what most people call colour, Value - the gray level component of the colour, and Chroma - the intensity of the colour. In this scientific conceptualization the gray level provides the central vertical axis as shown in Fig. 12 with the Munsell subtractive colour space which was specified in the early 20th century. Tektronix simplified these three perceptual colour axes into the HLS additive colour space which is symmetric. HLS, Fig. 13, is particularly well suited for use with computer display systems, and is very easy to use with the analytical visualization approaches discussed above.

Fig. 12. Munsell Subtractive Perceptual Colour Space

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Harold Moellering

Fig. 13. HLS Double Cone Colour Space, invented by Tektronix in the 1980s

More sophisticated is the TekHVC, Fig. 14, which in addition to using the perceptual colour axes, but also scales them into asymmetric colour increments similar to that of human vision. This is a much better rendition of digital perceptual colour for computer generated displays. Sadly, it is not widely used because few have licensed the Tektronix patents for TekHVC. More potential for the future.

Fig. 14. The TekHVC Perceptual Colour Space, Patented by Tectronix – 1980s

9 Some interesting visualization examples Following are several selected 3-D visualization examples from the meeting presentation. They are all from planetary space in the North


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American context, and are intended to illustrate some of the flavor of some of the ideas discussed above. The first, Fig. 15, shows an image of the Apollo 15 landing site on the Moon. The figure integrates planar insets of the Moon topography showing the location of the landing site along with two 3-D images of a specific location in that area where the lunar explorer vehicle traversed. Here one is linking together several images to provide better context and understanding of this Moon landing and exploration.

Fig. 15. Digital photogrammetry with scanned film images (colour version on CDROM)

The subject of Fig. 16 is that of the Mars landing and exploration. The major image of the Victoria Crater is an anaglyph that can be seen in true 3-D, thereby providing a better understanding of the crater surface. Linked to this 3-D anaglyph is a 3-D image of the landing shell of the Mars rover which adds context to the main image.

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Harold Moellering

Fig. 16. The worst place on Mars for stereomatching (colour version on CDROM)

The third image, Fig. 17, shows two related 3-D perspective images of the Victoria Crater on Mars. The left image is in 3-D perspective with shadowing from a calculated light source. It uses simulated colours to resemble the natural environment in that area. The right image shows the entire Victoria Crater in 3-D perspective, now with the slope angles shaded in a colour sequence. This is an example of analytical visualization being used to bring our a particular characteristic of this surface, here the slope angle of the surface. These two images together provide a better understanding of the Victoria Crater than either image alone. This illustrates the advantage of using analytical visualization as part of a 3-D display strategy.


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Fig. 17. Mars – Perspective Views

With these three selected visualizations one can begin to see the strategy of analytical visualization in action.

10 Summary and conclusions Analytical visualization has a rich history, beginning with predecessor work in ancient times and analytical work beginning the in the 19th Century with the work of Cayley and then Wiechel. With the advent of computer processing in the 1950s there emerged a more practical way of processing and implementing these strategies. Several key innovations in computer graphics in the 1970s such as homogeneous coordinate axes, homogeneous matrix transformations and effective visible surface algorithms spurred on the visualization developments. At the same time a host of innovations in spatial data concepts including various spatial data structures including square cells, topological data structures such as TIN models, and topological surface networks such as Warntz and Pfaltz surface networks greatly contributed to the ability of spatial science to more effectively organize, process and visualize spatial data. These developments go hand in hand with the concept of Real and Virtual maps, the 16 transformations between them, and defining interactive spatial data system design and processing with them to provide additional insights into spatial data processing and visualization. Then include the concepts of Deep and Surface Structure, and Nyerges Data

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Harold Moellering

Levels to achieve additional insight to the design and operations of spatial data systems. True digital 3-D stereoscopic visualization with spatial data has been going on since the 1980s, as evidences by the presented work of Prof. Moellering with the Tektronix 3-D stereoscopic workstation. This brings up some strategies of analytical visualization that include adding some computer analytical aspects of the phenomenon, surface, or scene that in some way enhances the understanding of the overall 3-D scene. This also includes the use of perceptual user colour spaces of HLS, TekHVC and related colour spaces that are a distinct advance over the RGB colour models that cater to the computer display hardware instead of the user. Together these concepts and innovations provide for a more powerful kind of spatial visualization that enhances true 3-D visualization with various kinds of analytical visualization.

11 Future prospects From all of these discussions above, it is incumbent to provide some suggestions for future research in this area of true 3-D visualization. The first is to continue to extend current 3-D visualization to include faster and more comprehensive 3-D visualizations with a higher resolution. These goals can be achieved with faster computer hardware, improved display algorithms, and better display hardware. The invention of the lenticular display screen is an excellent example of this work. One can also see continued work to utilize and extend analytical visualization. Here additional calculated characteristics of surfaces, objects or other scenes can enhance the understanding of the original 3-D visualization. It offers a path towards better scene understanding. While efforts are being made to extend the scientific and technical aspects of 3-D visualization itself, one can also think of additional subject matter domains for further research. The first is of deep space. Much progress has been made in planetary 3-D visualization as better data becomes available. This effort should also be directed towards deep space as those explorations and subsequent spatial data become available. The second is in the inner space of deep structure. Here more research should be directed towards visualizing the deep structure aspects of spatial scenes and objects. A simple example is spatial metadata. Many additional possibilities in the domain exist.


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Acknowledgements Several images in this paper have come from cooperating colleagues and organizations. I want to thank the American Congress on Surveying and Mapping (ACSM) for the image from Auto-Carto 9 that was published in the ACSM Bulletin in June, 1989, and Dr. Randy Kirk of NASA/JPL for the Moon and Mars images.

References Cayley A (1859) On Contour and Slope Lines, The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science, XVII, pp 264-268 Horn B (1982), Hill Shading and the Reflectance Map, Geo-Processing, 2, pp 65146 Moellering H (2000) The Scope and Content of Analytical Cartography, Cartography and Geographic Information Science, Vol. 27 (3), pp 205 - 223 Nyerges T (1980) Modeling the Structure of Cartographic Information for Query Processing, Unpublished Ph.D. Dissertation, Ohio State University, Columbus, Ohio 203 pp Wiechel H (1878) "Theorie und Darstellung der Beluchtung von nicht gesetzmässig gebildeten Flächen mit Rücksicht auf die Bergzeichnung, Civilingenieur, 24, pp 335-364

Section 1: Data and Techniques for True 3D Visualization

How true is true-3D? – Geometry between Single Image Stereograms and Lenticular Foil Displays Weiss, G. and Buchroithner, M. F.

Survey of True 3D and Raster Level of Detail Support in GIS Software Bektaş, K., Çöltekin, A. and Straumann, R. K.

Think Differently: a New Method to Create Lenticular- and Integral-Pictures Stendel, D.

Truly modelling reality…? – Let’s improve our cognitive maps with a bastard mix of algorithms to “undo” pictures, isometric mapping, high-density diagrams and comic culture as integral sign posts for software development in cartography Fritsche, N. -C.

How true is true-3D? – Geometry between Single Image Stereograms and Lenticular Foil Displays

Gunter Weiss1 and Manfred F. Buchroithner21 1

Institut for Geometry, Dresden University of Technology, Dresden, Germany 2 Institute for Cartography, Dresden University of Technology, Dresden, Germany

Abstract 3D visualization has a long tradition and it starts when people made 3D models of objects of their interest. Besides the symbolic or religious content of 3D “models” known from early Stone Age already in the Ancient World there occurs the need for technical visualizations, plans and models in architecture, mechanical engineering and even cartography. Our interest aims at these technical visualizations and their modern versions, e.g. anaglyphs, single image stereograms and lenticular foil displays. We will distinguish between visualizations showing 3D effects, like perspective drawings and photographs, visualizations showing 3D objects, like anaglyphes and lenticular foil displays, and visualizations showing “true” 3D objects, like 3D models. The main goal of this paper is an analysis of what kind of object can be seen in technical visualization. Key words: geometric visualization, central projection, lenticular foil displays, single image stereograms This article represents an updated Version of the contents of the lecture the first author gave at the ICA Symposium on “True-3D in Cartography”, Dresden, 24-28 August, 2009. 1


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Gunter Weiss and Manfred F. Buchroithner

1 Introduction When talking about 3D visualization one has to start with sculptures like the Venus of Willendorf (~25000 BC) and with paintings on rocks making use of the rocks’ natural relief like those in the caves of Altamira (~30000 BC). There is always an interaction between the visualized object and the human interpreter based on psycho-physiological facts, the so-called depth-cues (see e.g. (Buchroithner 2007)), and his or her pre-knowledge and obviously also modern visualizations are interpreted on the bases of pre-knowledge and inborn psycho-physiological properties of human interpreters. Already in the Ancient World there was a need for “technical visualizations” in architecture, mechanical engineering and even in cartography. Here we face another important aspect: The producer of the plan, map or model has to simplify. Such simplifications often have their reason in the different scales of model or in different material and more. Visualizations are, similar to mathematical modelling, therefore by necessity always abstractions of the physical world and thus the concept “true 3D” has to be taken with a pinch of salt from the very beginning! Based on the mentioned crucial facts, abstraction on one hand and interpretation on the other, we compare classical visualizations showing a 3D effect, like perspective drawings and photographs, with visualizations showing 3D objects like anaglyphes, single image stereograms (SIS) and lenticular foil displays (LFD), and visualizations showing “true” 3D objects, like 3D models.

Fig. 1. The central embodiment represents the famous Eiger Northface in Switzerland, based on a data model generated at the Institute for Cartography, Dresden University of Technology, Germany

The question is, in what sense a visualization is “true 3D”, how does pre-knowledge and training effect the interpretation and how far can abstraction go when producing a 3D visualization. Finally one may ask, to which degree the needed effort to produce a 3D visualization is worth the

How true is true-3D? – Geometry between Single Image Stereograms and Lenticular Foil Displays 25

effort and expenses for, say, an unbiased interpreter. At present most of the 3D visualizations need either an expensive apparatus to “simulate” threedimensionality, like “caves” and “holography” with the need of head sets or at least polarized glasses for the viewer, or comparatively high costs for producing 3D models, e.g. by a Rapid Prototyping Systems. Up to now single image stereograms (SIS) and lenticular foil displays are the only 3D visualization methods in two dimensions, which are not stationary and do not require any additional viewing aids, (provided we consider the coherent light required for the optimal observation of holograms also as viewing aids). Single Image Stereograms (SIS) are based on the viewer’s eyes fixing a point far behind the picture plane while accommodating to the distance of this picture plane. For most people this technique is not “natural”, as the convergence angle of the two optical axes of the eyes automatically adjusts also the accommodation of the eyes’ lenses to a suitable focal distance. If the viewer is successful and finally can see a 3D object, he or she can never be sure about the “real” dimensions of the object. A slight change in the position of the viewer V with respect to the SIS leads to another position of the seen 3D object O, but also to a slight deformation of it. Bigger changes in the position of V would have the consequence that one cannot find and see an object O at all or perhaps see a topologically deformed new object. So this 3D visualization method flourishing during the eighties of the last century has only restricted applications, e.g. for “fun pictures”. But the principle of SIS can be used as the basis for the more advanced 3D visualization by means of lenticular foil displays (LFD), see e.g. Fig.2.

Fig. 2. Photography of an LFD map. It delivers “pseudo-three-dimensionality”

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Lenticular Foil Displays (LFD) avoid the tiring effects of wrong distance accommodation with respect to more or less parallel optical axes. Here, under a system of parallel half-cylindrical shaped lenses, two stereoimages I1 , I 2 of an object O are sliced in stripes and are alternately posed under these parallel half-cylindrical lenses (= interlacing). The lenses make accommodation and convergence fit together once we look onto the LFD. To recognize a relatively sharp 3D object Oc we have to look at the LFD from a suitable distance and keep the display such that the lenses are orthogonal to the connecting line of our pupils. There is always only a certain region around the main viewing ray – the ray orthogonal to the LFD through the midpoint of the two pupils – where one can see a 3D scene relatively sharply. Outside this region or viewed from the wrong distance the impression is rather blurry. Slight changes of the eyes’ position with respect to the LFD will cause deformations of the seen 3D object Oc , and these deformations even may accumulate to discontinuous jumps. While these deformations are irrelevant for standard “fun pictures”, they are certainly of essential importance for cartography.

2 Mapping and interpretation of images A planar visualization Oc of a 3D object O is the result of a restricted mapping M of the (Euclidean) 3D space to a two-dimensional (Euclidean) image plane. Restricted mapping means, that the more or less globally defined mapping is only applied to O. For the analytical treatment the (Euclidean) 3D and 2D space have to be endowed with a (Cartesian) coordinate frame with given units, such that represents the analytical description of the mapping. In most cases M is modelled as a linear mapping procedure. A person looking at the image Oc should interpret it in the right way, namely connect Oc with the correct original object O. Here we distinguish between a Naïve Viewer having only a personal cultural background and an Expert Viewer, who has an educational background and perhaps training in addition. For example, for a trained medical doctor the interpretation of an x-ray or an ultrasound image should cause no problems, while a naïve viewer will perhaps recognize nothing. The person designing the 2D visualization via computer graphics algorithms or via classical descriptive geometric methods must take into


consideration, to whom s/he addresses, the naïve viewer or the expert. He also should know about theoretical and practical reconstructability of O from Oc , e.g. via photogrammetric tools or by “hidden assumptions”. Such hidden assumptions concern e.g. orthogonality of lines and planes and are responsible for that we can readily interpret axonometric or perspective images in a correct way. For classical photogrammetric reconstruction we need at least two (linear) images Oc and Occ of O. A designer or artist wants to share her/his original idea O with other people. S/he looks for a visualization, which will represent this idea unambiguously. On the way to the realized art object Oc s/he will have to simplify, to abstract and adapt the original idea and finally use production algorithms and cope with their limits. Between O and Oc s/he has to solve a pedagogical task, i.e. the manipulation of tools and of materials. The following set of pictures Fig. 3, due to the U.S.-American artist Robert A. Wiggs (see e.g. (Wiggs 1990) shall symbolize this path from O to Oc from the viewpoint of an artist.

Fig. 3. Robert A. Wiggs’ “shapes” showing a path of 3D visualization in arts: Idea – Abstraction – Algorithms – Object

3 Principles of planar 3D visualization Already at the beginning of the 19th century Gaspar Monge developed a theory of two-dimensional visualization of 3D objects, namely Descriptive

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Geometry. The aim was and still is to solve 3D intersection and measuring problems directly in the drawing plane. So the drawing plane must become a model for the 3D space. In the sense of G. Monge one needs (at least) two images of the 3D space, which at his time was always meant to be a Euclidean space. Such two images are e.g. provided by a pair of front- and top-projection in the drawing plane. A more general pair of images, namely two photographs (representing linear perspective images, but performed by an optical/physical apparatus), is used for photogrammetric reconstruction of the mapped object O. This reconstruction of the preimage O to a so-called Two-Image-System ( Oc , Occ ) can be performed by (a) descriptive geometric methods, by (b) (computer aided) numerical calculation or by (c) an “analogue” optical/physical method like the stereocomparator of Carl Pulfrich (1901), c.f. (Gosh Sanjib 2005). The only assumption is that one can identify corresponding pairs of image points in such a given Two-Image System. Additional information might be camera data and the position of the camera when the photographs were taken. Such additional data can simplify the calculations and may also lead to higher accuracy.

Fig. 4. Diagram of mapping and reconstruction/interpretation

Classical descriptive geometry can be used for making an axonometric image Oc of an object O. Usually we understand such an image Oc as a parallel projection of O. (The axonometric imaging principle yields in a


wider sense and can be connected with central projections, too. But then it is common use to speak of central axonometry.) In our society we are well trained to “read” oblique parallel projections of an object O and will intuitively understand parallelity of lines in the image plane as stemming from parallel lines in space. If a coordinate frame is mapped together with the object, it is also easy to “reconstruct” proportions or even measures. Standardised oblique projections of a cube like object are often used in intelligence tests, compare e.g. (Tsutsumi et al. 2005). This shows that one generally assumes that also naïve viewers can pull the right conclusions from such standardised images. On the other hand, one can play along with parallel axonometric images by locally changing visibility, thus receiving a so-called impossible. Here the confusion of not being able to reconstruct an object is the aim of such a mapping. The impossible three-bar and the impossible crate are well-known objects of that sort. Naïve viewers will hardly find the unexpected objects O, which will correspond to the images and they will always find it a geometer’s trick when they are shown the actual physical 3D objects. In this category fall paintings of Victor Vasarely, e.g. Fig. 5. Here a planar picture “must” be interpreted as an image of a 3D object. But there are two partial solutions for such an “impossible” object. Psychological facts and maybe our image- and paperbased education let the painting less probably occur just as a planar colour scheme then an image of something three-dimensional.

Fig. 5. One of V. Vasarely’s twodimensional paintings, which (locally) allows two 3D interpretations. (Reproduction of a postcard)

Fig. 6. Single image (one eye projection) with 3D effect. “Frontal perspective of the stadium in Firence” (Hohenberg 1961)

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From the above described behaviour of a naïve viewer of an impossible we can learn, how strong we all obey unconscious and hidden assumptions, when interpreting drawings or other images! From perspective drawings it is much harder to read off proportions and measures as long the viewer is not an expert. But when looking onto such pictures one can hardly avoid to “see” a 3D object. When invented in Italy during the Renaissance perspective painting was seen as an optical illusion and in the following centuries these effects were excessively exhausted. As an example we show a drawing of (Hohenberg 1961) in Fig. 6. While geometric visualizations like that of Fig. 6 deal with proportions and distances and are mostly “true” images of a situation in 3D space, visualizations in chemistry or physics often have a rather symbolic or allegoric meaning, they visualize what nobody has seen or touched and they make great efforts in psychology and didactics to enable the naïve viewer to grasp the clue. Extraordinary visualizations of this kind can be found in (Hawkins 2002) (see e.g. Fig. 7).

Fig. 7. Allegorical visualization of astro-physical facts based on a didactical idea and classical perspective projection. (Stephen Hawkins: “Simultaneous Relativity – Relative Simultaneousness“ (2002), (Hawkins 2002)

We notice that besides the relations between positions of points and objects in the Euclidean space there are hidden and obvious assumptions packed into a visualization. The viewer interprets the visualization after having put it into a certain context, be it the explicit verbal description of what should be seen in the picture, be it the viewers own knowledge or imagination. These facts rule of course also visualizations in Cartography.


4 Hidden and obvious assumptions in planar visualizations We have already mentioned that an object O can be reconstructed by photogrammetric or by geometric methods from one (linear perspective) images Oc , if one assumes sufficiently many geometric properties of O. In architectural photogrammetry such assumption mostly concern planarity and orthogonality of faces of O. There are reconstruction theorems of the form: Can we identify sufficiently many image points where one knows or assumes the position of their original points in space, then we can reconstruct the originals P of points P’ under the assumption that P belongs to an already reconstructed plane or line. As an example we show the 3D reconstruction of a painting of the Russian constructivist Jacov Chernikov, see (Lordick 2003).

Lars Nestler: 3D reconstruction Fig. 8. Architectural photogrammetric 3D reconstruction of a scene depicted by Jacov Chernikov (1933) (at right); courtesy (Lordick 2005)

A similar statement can be used even for objects in higher dimensional spaces. As an example we take Laszlo Vörös’ images of special “Zonotopes” Oc in 3D space, see Fig. 9 and (Vörös 2008). This objects are the orthogonal or skew projections of a hyper-cube O of a multidimensional space mapped into a 3D space. Finally Oc is again mapped by front-top- view projection to two images. While the expert viewer immediately “reconstructs” the right object, namely the zonotope

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as well as the original hypercube, a naïve viewer is lost and cannot handle the hidden information.

Fig. 9. Multidimensional Cube O mapped to an object Oc in 3D space, which again is mapped by front-top-view projection. (Laszlo Vörös, “Zonotopes”, courtesy (Vörös 2008)

5 Geometric fundamentals of two-image systems In classical photogrammetry we speak of the (two different) camera positions Z1 , Z 2 , together with the camera image planes S1 , S2 as the “main configuration in space”. The two images X i Si , i 1,2 of an object point X are then mapped into a pair of points ( X ', X ") in the final two-dimensional image plane, the “map” S. These mappings Ni : Si o S usually are either similarities or affine or even collinear transformations. We consider the most general case, namely that they are collineations. The line Z1Z 2 is called the “kernel axis” z of the two-image-system and it intersects S1 in the first image Z 21 of the 2nd projection centre Z 2 . Similarly, S2 z : Z12 is the 2nd image of the 1st projection centre Z1.


Fig. 10: Principles of 3D reconstruction based on a two-image-system

The Ni -images of these special points are called the epipoles (kernel points) of the two-image-system, a concept coined in Computer Vision, c.f. (Stachel 2006) and (Hartley and Zisserman 2000). The lines o ': X ' Z2c and o ": X " Z1 " are called epipolar lines (order lines). We can describe the mapping as restriction of the product to the pencil of lines {o '},{o "} through the epipoles. Thereby persp stands for the perspectivity from the lines {o1 : N11 (o ')} to {o2 } via the double-projecting planes {Z1Z 2 X }. Therefore one can conclude that E is a projectivity, i.e. a cross ratio true linear mapping from one pencil of epipolar lines to the other, see Fig.10. The system {Z 2' , Z1" ; E} is called the “main image-configuration”. If this main image-configuration is not given a priori, the first task in photogrammetric reconstruction is to solve the “problem of the projectivity”, namely to reconstruct {Z 2' , Z1" ; E} from sufficiently many pairs ( X ', X ") of points X. A well-known theorem in photogrammetry is (see (Tschupik and Hohenberg 1972)). Theorem 1: a) Given 7 image pairs ( X ', X ") of points and a main spaceconfiguration {Z1 , Z2 , S1 , S2 } , then the photogrammetric reconstruction of any set of points X in space from their image pairs is a cubic problem, as long as the reconstructed points X are not all belonging to a “critical surface”. b) Critical surfaces are: cylinders of revolution, cones over circles having a generator orthogonal to the circle’s plane (so-called orthogonal cones), hyperboloids of one sheet having such an orthogonal cone as asymptotic cones, and orthogonal hyperbolic paraboloids.

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c) The reconstructions to two different main space-configurations are collinear, i.e. there exists a collineation mapping of one reconstruction to the other. Once we know the camera data, the reconstruction includes the Euclidean structure, too, and the main space configuration to the twoimage system is, mathematically speaking, unique.

6 Remarks on geometric optics In this chapter we will talk about the influence of an optical apparatus on 3D reconstruction. In (school-) physics explanations of the lens equation are always supported by drawings like Fig. 11: They mostly show an arrow posed on the optical axis and orthogonal to it and its image arrow. The essential conclusion, namely that an object O is transformed into a collinear object Oc of it, is not mentioned explicitly. Thereby the transformation N is a perspective collineation with the lens centre Z as centre and the main plain of the lens as axis z. For a symmetric lens system Z z and N is a so-called elation. This is in fact trivial fact, which also explains the phenomenon of the depth of focus only, seems to be explicitly described first in a recent dissertation, see (Fuchs 2007, c.f. also Glaeser 2007). P

Qc Z F

F Pc

Q z

Fig. 11. A lens transforms an object into a collinear transform of it

Lenticular foils consist of cylindrical lenses. In terms of geometry the above mentioned collineation N is then an axial perspective collineation with one undistorted direction. Even the lens radii are very small and the objects O are distorted to “almost flat” image objects Oc, one had to consider this axial collineation N to create maximally sharp images. In common visualizations and descriptions of the principles of LFD one will miss such a consideration, cf. e.g. (Stendel 2008, 2009) and Fig. 12. When looking at such an LFD scene, the viewer automatically positions


her/himself to an optimal distance from the LFD; s/he will still have the impression to see only that region sharp, where the rays meet the LFD in an angle not too far from 90°.

Fig. 12. The principle of LFD and of interlacing left and right images

Here the “mind-intern” correction of distorted or blurred objects does not work so perfectly. But when comparing the perceived impression of an LFD scene with that of a photograph of it one immediately understands what our mind unconsciously accomplishes in terms of in 3D reconstruction. The problem of how to cut a pair (or, more advanced, a sequence) of stereoscopic images into slices and to put them correctly under the foil is usually left to the printing houses. They use commercial software, and there is hardly a possibility to influence this soft- and hardware via academic research. As mentioned in the introduction, Single Image Stereograms (SIS) are somehow of provisional nature, and LFD can be seen as their advanced successors. Fig. 13 is an example of a SIS clearly showing the interlacing principle.

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Fig. 13. Single Image Stereogram – a precursor of LFD, (author unknown)

In contrary to SIS LFD scenes avoid the eye stressing “wrong” lens accommodation. Only comparatively few people come to recognize the relatively “poor” objects encoded in a SIS (cf. Buchroithner 2007). Sometimes it helps to know, which object should be seen. If one is lucky enough to see the object O, a slight movement of the head will cause a deformation of O according to Theorem 1(c). So the collinear deformation occurs also, when a simulated 3D object is seen and not only when looking at a painting or drawing! Theorem 1(c) allows us to geometrically confirm a well-known observation: If the viewer of a figure drawn in central projection or simply of a photograph changes his or her position with respect to the image, the new 3D interpretation will be a collinear deformation of the first interpretation. More understandably formulated, when passing by a portrait, where the depicted person looks straight to the viewer, one gets the impression that the portrait’s eyes keep following the viewers movement. The viewer “reconstructs” a collinearly deformed person, but still identifies it with a “correctly formed” human body. This correction takes place in our mind. It is in fact the unconscious application of a collinear transformation to


perceive a 3D interpretation with maximum likelihood. Perspective images of architectural scenes in frontal central projection show the same effect. (Thereby frontal central projection is not essential, the phenomenon occurs in any perspective projection.)

7 Remarks on phenomena related to 3D interpretation The inborn human behaviour to unconsciously “regularise” objects reconstructed in mind is exploited in the so-called relief perspective, a modelling technique widely used in arts, architecture and for stage sets. Fig. 14 shows a rapid prototype model of a reconstruction of Maxentius’ Basilica in Rome seen from the backside and from inside. Until now we have described the phenomenon of collinear deformation of a virtually reconstructed object in two different cases: when looking at planar images and when looking at SIS- or LFD-supported virtual 3D objects. When looking at physical 3D object O the changing of the viewer’s position leads to another view of O, and it is a matter of maximum likelihood to assign both views to the same object. But the views could also stem from different objects!

Fig. 14. Rapid prototype of a relief Oc of a collinear object O seen from backside and from inside (author Daniel Lordick, TU Dresden, 2005)

In the example below the first author stumbled over an interesting incidence, a sculptured concave portrait showing the optical illusion of “convexity”, even when seen with both eyes and at a very oblique angle (see Fig. 15).

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Fig. 15. Granit sculpture of an unknown artist showing the optical illusion of convexity even the portrait is concave. Oslo, Rådhusgate (photographs G. Weiss 2009)

The experience that one sees a 3D object X with both eyes and from these both views “reconstructs” in one’s mind a wrong object Y is alarming: How can we be sure that our seen true-3D-objects are free from such artefacts?

Fig. 16. Photographs of LFD maps (map details of Austria and of Mars), courtesy of mbmSystems, Dresden.

It seems to be necessary to do more research on the human perception of true 3D visualizations as well as on the position-dependent deviation of the recognized 3D object from the depicted one. Photographs of an LFD scene seem never as sharp as the scene occurs to the viewer (cf. e.g. Fig. 16). An LFD scene gives a 3D impression, also when viewed with one eye only.


For a camera as a technical surrogate of the single-eyed viewer this phenomenon does not exist, see Fig. 16 (left). But as we are used to interpret shadows as a sort of a second image and can therefore rely on the reconstructability property of a two-image-system, we “see” a 3D object also with one eye, (see Fig. 16, right). Fig. 16 (left) shows a map in classical hypsometric elevation colouring and, by our education, we are used to pull the right conclusions about the terrain altitudes. So most people are well trained enough to “see” already a planar map as a relief. For those people the profit of an LFD map does not compensate for the drawback of blurred areas. In addition, when the viewer moves, the landscape moves in the same direction, thus contradicting the impression of the contragredient movement seen in physical 3D scenes. In this context an interesting observation may be described A final remark: In his lecture “3D Terrain Visualizations for GIS” at the ICA SPIE Europe Symposium “True-3D in Cartography” in Dresden, Germany, in August 2009 Rozinoor Che Mat showed maps with an unusual hypsometric colour tinting from yellow to blue, depicting the highest mountain regions in dark blue. Most of the auditory being used to associate dark blue with “deep se” got no or wrong 3D impressions.

8 Conclusion Playing the role of a advocatus diaboli we posed and analysed the question, “What kind of object Oc do we see? How is it related to the original object O?” These problems are still to be answered not only for LFD scenes. In detail, the following problems arise: As long as we have the original stereo-images I1 , I 2 together with some camera data we can reconstruct the original object O using photogrammetric methods. Thus a possibility to compare O and Oc would be to use a stereo camera to take pairs of pictures of an LFD scene seen from a certain camera position and reconstruct Oc from the photographs again by photogrammetric methods. By changing the position P of the stereo camera set we receive different objects of type Oc, and we can then connect a “deformation matrix” M ( P) with the camera position. Thereby we assume that an approximating linear deformation O o Oc, i.e. a “collineation”, suitably describes the divergence of O and Oc. This

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assumption is somehow natural, as the geometric reconstruction of an object O represented by two images of a so-called “two-image system” delivers O only up to (projective) collineations. Thereby geometric reconstruction means a photogrammetric reconstruction without camera data. Future research work of the authors will go in this direction. There will always remain an “uncanny gap” with contradictions to movement/depth parallax or/and contradictions to eye accommodation and convergence. It is the aim of the envisaged research to accept and try to minimize the uncanny gap! In the future, 3D visualization by means of LFD will gain increased importance not only for cartography. One can suppose that advanced advertisement will soon use this technique, too, and even for technical handbooks and assembly instructions LFD can be useful. For the moment accuracy problems arise from cartography alone. However, also the private sector with the wish to “three-dimensionalise” its photographs poses demands on accuracy. LFD representation of an object O still is cheaper than its physical representation by Rapid Prototyping. Furthermore, LFD are easy to handle and to store. Now one also has a relatively simple medium to visualize a 4D object O by two or more 3D images of it and train the imagination by looking at sort of a 3D top-front-view projection Oc, Occ of O. Here the LFD technique also opens up new horizons for a 4D descriptive geometry. Some final Cassandra Remarks: Statistics tell that approximately two thirds of Central Europeans cannot spontraneously retrieve relief information from a classical map (Buchroithner 2007). It is not sure to which degree LFD maps can help the map-illiterates or “map-blind” people. But it is certainly worth a try. Another aspect is: Does our brain really need support in something it can do alone? Does not a 3D navigation system with high level of details cost much “brain-energy” to reduce the data spam to essential information: “Turn left right now”? Finally we state: Yes, we want high fidelity in True-3D Cartography, in spite of the unavoidable uncanny gap!

References Buchroithner MF (2007) Echtdreidimensionalität in der Kartographie: gestern, heute, morgen. Kartographische Nachrichten 5: 239-248 Buchroithner MF, Wälder O, Habermann K, König B (2003) Generating a True3D-Image Map of High Relief Terrain using Lenticular Foil. e-publication

How true is true-3D? – Geometry between Single Image Stereograms and Lenticular Foil Displays 41 http://www.mountaincartography.org/publications/papers/ica_cmc_sessions/3 _Durban_Session_Mountain_Carto/1_Durban_Buchroithner.pdf Fuchs G (2007) Geometrisch-physikalische Analysen zur Evolution des Sehens bzw. das Sehen von Gegenständen beim Blick in einen doppelt gekrümmten Spiegel. PhD-Thesis, University of Technology Vienna Glaeser G (2007) Praxis der digitalen Makro- und Naturfotographie. Spectrum Akademischer Verlag 2008, ISBN 978-3-8274-1906-4 Gosh Sanjib K (2005) Fundamentals of Computational Photogrammetry. ISBN 81-8069-187-X (HB), New Delhi Hartley R, Zisserman A (2000) Multiple View Geometry in Computer Vision. Cambridge University Press Hawkins St (2002) Das Universum in der Nussschale. Hoffmann & Campe Verlag, ISBN-10 3455093450 Hohenberg F (1961) Konstruktive Geometrie in der Technik. (2nd ed.) SpringerVerlag Wien. Lordick D (2003) Tschernichow Revisited – 3D-Modelling Studentenarbeiten. Dresden, ISBN 3-86005-398-1 Lordick D (2005) Reliefperspektivische Modelle aus dem 3D-Drucker. IBDG, Heft 1, Jahrgang 24 (Innsbruck 2005): 33–42. Mat Rozinoor Che (2009) 3D Terrain Visualisation for GIS A Comparison of Different Techniques. Lecture at the ICA SPIE Europe Symposium, True-3D in Cartography Dresden Stachel H (2006) Descriptive Geometry Meets Computer Vision – The Geometry of Two Images. JGG 10, No.2: 137–153 Stendel D (2008) Autostereoscopic Visualisation of Landscape. In: Buhmann E Digital design in landscape architecture. Wichmannverlag Heidelberg Stendel D (2009) Think different – New methods to Create Lenticular- and Integral-Pictures. ICA SPIE Europe Symposium, True-3D in Cartography Dresden Tschupik J, Hohenberg F (1972) Die geometrischen Grundlagen der Photogrammetrie. In: Jordan, Eggert, Kneissl eds Handbuch der Vermessungskunde. III a/3, 10th edn, Stuttgart: 2235–2295 Tsutsumi E, Schröcker H-P, Stachel H, Weiss G (2005) Evaluation of Student’s Spatial Abilities in Austria and Germany. JGG 9 (1): 107–117. Vörös L (2008) n-Zonotopes and their Images: From Hypercube to Art in Geometry. Proc. ICGG 2008 Dresden, ISBN 978-3-86780-042-6 Wiggs RA (1990) Agents of symmetry in operation. Symmetry Culture & Science vol 1: 341–355

Survey of True 3D and Raster Level of Detail Support in GIS Software

Kenan Bektaş, Arzu Çöltekin, Ralph K. Straumann GIScience Center, Department of Geography, University of Zurich, Switzerland

Abstract Principles of stereoscopic vision have long been used in geographic data processing and visualization. In recent years, a number of mainstream digital devices and systems with stereoscopic capabilities are marketed to public, making True 3D visualizations more accessible. This trend may potentially impact how spatial data is visualized in everyday life. In lowbandwidth environments, however, level of detail (LOD) management approaches have to be applied for efficient processing of large -True 3Dspatial datasets. In order to outline future research needs in True 3D visualizations, this paper presents a survey on current support provided in common Geographic Information Systems (GIS). The survey is designed to document whether the visualization modules of the selected systems a) can display 3D b) can display stereoscopic 3D c) can manage different levels of detail when displaying raster graphics. We document the names of visualization modules and report the types of stereoscopic operations, stereoscopic viewing methods and raster LOD management approaches in surveyed software. The analysis shows that all surveyed GIS support nonstereoscopic or stereoscopic 3D visualizations and a form of raster LOD management. Present raster LOD techniques in the surveyed systems are efficient for level switching when scale changes, however, unlike in other graphics processing software, none of them utilize human visual system inspired approaches. We hope that findings from this study will allow both M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_3, © Springer-Verlag Berlin Heidelberg 2012

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Kenan Bektaş, Arzu Çöltekin, Ralph K. Straumann

researchers and practitioners to assess the current state of True 3D and raster LOD management support in widely used GIS software. Keywords: GIS Software Survey, True 3D, 3D Visualization, Stereoscopic Visualization, Level of Detail Management, Geo-Virtual Environments

1 Introduction and background

1.1 Motivation The availability of Geographic Information Systems (GISs) and the amount of spatial data and services increase continually. Visualization of geographic information is a crucial part of many applications developed in such systems or services. This has led geographic information (GI) scientists to establish research priorities for geovisualization, considering both the developments in visualization media and the growing amount of, and need for, geo-spatial data (Buckley et al. 2005; Goodchild 2009). In parallel, the market for True 3D with stereoscopic viewing solutions has been growing (Bitmanagement 2006; DeFanti et al. 2009; Hewage CTER; Kirschenbauer 2005; Samsung.com; Sharp Inc.), which further emphasizes the need for research into stereoscopic concepts and techniques to improve the visualization experience. Within this larger context, the objective of this paper is to assess the state of the art of mainstream GIS software regarding their capabilities in 3D visualization, stereoscopic visualization and raster Level of Detail (LOD) management. The findings about each of the GIS software are reported in a series of sections. Additionally, the results are presented in a summarised manner in Table 1, providing the reader with a quick overview. In the next section we present some definitions which are central to the topic at hand and the remainder of the paper. Subsequently, a brief review of recent visualization approaches in GIS software and services is presented. This is followed by an introductory text on the concept of LOD management for efficient visualizations. In the remainder of the paper the software survey methodology is explained and the results are presented with an integrated discussion. An outlook on planned further research concludes the article.


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1.2 Definitions Since the presented study involves several related but separate disciplines, brief definitions of the most relevant terms (in italics) are provided in this section. The term visualization expresses forming a mental or computational picture of a scene which is not actually present to the sight (Oxford Online Dictionary). In this paper, when the word visualization is used, it refers to a scene that is displayed using a digital system. Stereoscopy can be considered as a visualization (or viewing) method that takes the binocular nature of human vision into account (in its traditional sense, stereoscopy is the practice of using a stereoscope, an optical device that separates left and right images (Oxford Online Dictionary)). Combining the two terms, stereoscopic visualization describes the concept or process of using stereoscopic principles in an optical or digital environment to create a 3D image. The term True 3D has traditionally been used for 3D depictions that have three independent coordinate axes (Slocum et al. 2010). This was used to avoid confusion with 2.5D representations. In GIS, 2.5D is used for elevation modelling where altitude is represented as an attribute. In more recent texts, the term True 3D has also beenused to describe the visual experience in virtual environments (Kirschenbauer 2005; Wood et al. 2005). When used in a virtual reality context, it refers to 3D visualizations that create an immersive experience for the viewers (including stereoscopic displays and holograms) (Bodum 2005; Buchroithner 2007; Kirschenbauer 2005; Lewis et al. 1971). In True 3D systems, the virtual scenes are perceived in front of, or behind the physical screen, through various (physiological and psychological) depth cues (Kirschenbauer 2005). Throughout this text, we use the term True 3D to refer to configurations where stereoscopic visualization is enabled. 1.3 Visualization in Geographic Information Systems and Services Since the early days, when GIS started as a government enterprise (i.e., Tomlinson’s Canada Geographic Information System in 1962 (Baumann 2009)), it has gained wide acceptance also in industry, research and education (Baumann 2009; Gore 1998). A constant trend in producing cheaper hardware with increased performance (Liddle 2006; Moore 1998) has led to the development of more powerful GIS software. In the early 1990s, the combination of the Internet and spatial technologies has triggered the development of concepts like virtual globes (e.g., Google

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Earth, NASA World Wind) and online mapping services (e.g., Google Maps and Microsoft Bing Maps) (Gore 1998; Schweikart et al. 2009). GIS software are capable of creating, managing, analyzing and visualizing georeferenced information, while virtual globes and online mapping services are markedly less powerful in some of those areas (Duindam 2006). However, they provide many users the possibility of exploring the earth via 2D and 3D visualizations. Experts predict that the recent developments in both GIS and online geographic services will have a similar positive impact on GIScience as the personal computer has had on computer science thirty years ago (Butler 2006; Schweikart et al. 2009). 1.4 Level of Detail Management Approaches While geographic data and services are becoming widely available, their accessibility may be hindered due to its growing size. Therefore, storing, processing and, more particularly, transmitting it (over a limited bandwidth) are notable problems to be solved. Among several methods that have been developed for efficient visualization of geographic information, an important one (originating from computer graphics) is LOD management. In LOD management a complex object is constructed and stored at different resolutions. For visualization, the most appropriate representation is chosen in real time, in order to optimize the tradeoff between image fidelity and frame rate (Luebke et al. 2003). In managing the LOD, the software and/or the content provider takes practical and perceptual constraints into account (Coltekin, Haggren 2006). In vector environments, LOD management methods often involve simplifying complex polygonal meshes, while in raster environments they typically control the resolution of the images in order to strike a balance between computational needs and human perception. The selection of higher or lower resolution representations can depend on several factors including the distance of the object from the view point, the size of the object in screen space, the eccentricity of the object with respect to the user's gaze, the velocity of the object across the user's visual field, the priority of the object according to the user's interest (Luebke et al. 2003). For stereoscopic visualization, the important factor is the depth of field where the user's eyes are converging (Coltekin 2006; Coltekin 2009; Linde 2003). Since the early 1990s more researchers have turned their efforts towards developing algorithms which maintain the visual appearance as much as possible through respecting aforementioned factors (Luebke et al. 2003).


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To obtain a set of LODs for raster datasets various techniques make use of image pyramids (Fig. 1). For example, mipmapping is a heuristic for texture mapping where the rendered LOD of the texture is dependent on the distance between viewer and the object (Wood 2005). The mipmaps represent textures using an image pyramid in which each pixel is typically an unweighted average of the neighboring pixels in the next higher resolution level of the pyramid (Luebke et al. 2003).

Fig. 1. Example image of the Louvre Pyramid in Paris (left) and 6 levels of detail in the corresponding image pyramid (right).

Another raster LOD management example is the Multiresolution Seamless Image Database (MrSID) format (LizardTech). MrSID first performs a lossless encoding using wavelet transformation, then provides an optional optimisation and finally decodes the image selectively. During encoding, for every input image, multiresolution zoom levels are created. The decoding process works by running all encoder steps in reverse order and reassembling an image from appropriate zoom levels. LOD management offers strong image compression and is crucial in many applications. It is also used for displaying large geodatasets in virtual environments and is especially applied in low bandwidth configurations (realtime web based applications, mobile devices or car navigation systems) (Bodum 2005; Döllner, Buchholz 2005; Engin et al. 2009; Hüttner et al. 2005; Larsen, Christensen 2003; Lindstrom et al. 1996; Zach et al. 2005). On the other hand, LOD management for stereoscopic 3D has

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been studied much less than the conventional LOD methods. This is possibly due to its computational complexity and historically smaller market (Coltekin 2006; Luebke et al. 2003). Documenting the current raster LOD support in GIS software will make it easier to assess the current state of the art and reveal the potential or ease to transfer these and other new LOD management approaches to True 3D geovisualizations.

2 Survey Results

2.1 Method and criteria To establish the state of the art on any given subject, the most common practice is a literature review. However, approaches may also include expert interviews, questionnaires and in case of technical subjects, documentation of features of the software commonly used in the domain (Lemmens 2007; Reddy 1995). Especially in technology driven areas such latter methods may reveal more up-to-date information about a research subject than a literature review. Thus, based on a recent publication on GIS software (Steiniger, Weibel) and a market share study (Horsky 2007), we decided to do a survey on following software: ESRI ArcGIS, Intergraph GeoMedia, ERDAS, Autodesk AutoCAD, Bentley MicroStation, Pitney Bowes MapInfo, Quantum GIS (QGIS) and GRASS. The commercial software in our list seem to share among themselves a substantial part of the market (82%) and are significantly more popular than lower-ranking alternatives (Foundyller 2009; Horsky 2007). Open source software are typically not included in market share studies, however, in our survey, two commonly known open source software (QGIS and GRASS) are included to introduce diversity in the study. Note that stand-alone photogrammetry software is often capable of processing and visualizing stereoscopic imagery, too; however, they are not explicitly evaluated in this study. Modern GIS software is commonly expected to be able to process imagery and encompass all steps of handling 3D geographic information (Heipke 2004). To test this assumption and to quantify current GIS’ capabilities, our survey investigates following specific questions in a systematic evaluation: Does the software support 3D visualization, if so, is it via an internal (native) or external (third-party) module? The same question is also considered separately for stereoscopic visualization. A further step in the software survey is to document what kind of stereoscopic viewing the software allows (i.e., active or passive). In


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geovirtual environments, stereoscopic viewing requires intense computational interaction with a (dual head) graphics card. Hence, it is also relevant to document which GIS software support stereoenabled graphics cards. Finally we ask: Given the GIS software supports stereoscopic visualizations, does it have built-in algorithms to compress the data and does it support some form of raster LOD management? Through documenting whether these features exist or not, an overview can be obtained as to how commonly 3D and stereoscopic visualizations are implemented across the surveyed GIS software. The existence of such support (i.e., the tendency of companies to provide native or external implementations of these features) may serve as an indicator of the interest of the public in using these visualization options (i.e., the demand). If we observe a common trend for GIS software to support specific visualization features, it is supposed that such supply is met by a common corresponding demand. To answer the survey questions, software manuals, GIS and photogrammetry journals and news resources were analyzed. In some cases, company representatives were contacted via phone or email to obtain more information. In the following sections we document our findings, i.e., detailed information on 3D, stereoscopic and raster LOD management functionality for each software.

2.2 Results 2.2.1 ESRI ArcGIS

ArcGIS 3D Support. 3D Analyst is the extension of ArcGIS for the analysis and visualization of 3D vector and raster data. It supports all data formats used in Arc-GIS, including several image formats, shapefiles, geodatabases, CAD data and MrSID data. In addition to these, 3D Analyst supports MultiGen, OpenFlight and 3D Studio MAX formats for realistic representation of 3D features. Beside area, volume, slope, aspect, hillshade and several other calculations, an interactive and seamless navigation through multi-resolution image data is supported. By using ArcGlobe or ArcScene (two applications building on 3D Analyst) it is possible to visualize and analyze geographic information from global and local perspectives. The user can create animations and save them in MPEG, AVI or QuickTime formats. Additional features like distance-dependent drawing and LOD support enhance the user’s experience of 3D visualizations. In the ArcGIS family Raster Pyramids are the

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implementation of image pyramids, which are described in the section 1.4. They allow users to visualize different LODs depending on scale. Via 3D Analyst, ArcGIS newly supports so called terrain datasets which are multiresolution triangulated irregular network (TIN) surfaces stored as a pyramid-like structure (ArcGIS 3D Analyst; ArcGIS 9.2). ArcGIS Stereo Support. In the stereo viewing mode of ArcScene, it is possible to use anaglyph (requires red/blue or red/green glasses) or shutter glasses (requires a set of signal transmitter hardware), as well as polarised glasses in the so-called free viewing mode. Stereoscopic operations are supported with an external module called Stereo Analyst (developed by Leica Geosystems). Stereo Analyst is capable of collecting and revising spatial features from imagery in a stereoscopic environment. A Component Object Model (COM) application programming interface (API) allows the developers to implement applications that support external photogrammetric project formats. Stereo Analyst automatically identifies the graphics card in the system. If the graphics card is not stereo-enabled, Stereo Analyst displays stereo images in anaglyph mode. If there exists a graphics card supporting quadbuffered stereo, the scene can be viewed with polarised or shutter glasses in 3D. Stereo Analyst supports several 3D mice for efficient 3D work (Stereo Analyst for ArcGIS). 2.2.2 Intergraph GeoMedia

GeoMedia 3D Support. In GeoMedia, TerraExplorer Pro, TerraBuilder and TerraGate are modules dedicated to visualizing, managing and streaming 3D spatial data (Intergraph Corporation). TerraExplorer Pro is developed by Skyline Software Systems as a standalone application. The latest release of TerraExplorer 5.1.2 (as of August 2009) has visualization and analysis features including interactive drawing, importing and adding geometric shapes, user defined objects, text and labels on 3D terrain models, measurements for terrain analysis, creating snapshots and creating 3D fly-through animations in AVI format from flight paths. The Imagery Layer feature allows viewing multiple resolution levels of terrain imagery. It is also used to rectify source image files (e.g., Windows Bitmap (bmp), Tagged Image File Format (tiff), Graphics Interchange Format (gif), Joint Photographic Experts Group (jpeg, jpeg2000), MrSID (sid) and ERDAS Imagine (img) formats) to the coordinate system used in TerraExplorer. Additionally, an API is provided for developers to create extensions accessing external data sources (TerraExplorer). TerraBuilder creates photo-realistic 3D terrain databases using aerial photos, satellite images,


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terrain information, digital elevation models and vector data. It can support and import a wide range of image formats including gif, jpeg, jpeg2000, tiff, bmp, img, user-defined binary raw, sid and Enhanced Compression Wavelet (ecw). TerraBuilder is able to merge datasets of varying resolutions and sizes. It can apply colour adjustments, area selection and clipping operations. Resulting 3D databases can be enhanced with 2D and 3D dynamic or static objects and can be streamed over a network or accessed offline (TerraBuilder). TerraGate is the application specialised in streaming 3D terrain data over networks to remote TerraExplorer users. It offers an optimised data transfer for low-bandwidth connections and is compatible with TCP/IP and SSL protocols, firewalls and proxy servers, and takes advantage of multiprocessor server hardware (TerraGate). On the 2009 GeoMedia international user conference, GeoMedia3D has been announced as a new product that will come to market in 2010. GeoMedia3D will integrate 3D visualization capabilities natively into GeoMedia (Intergraph User Conference). GeoMedia Stereo Support. ImageStation Stereo, the registered product of Z/I Imaging (acquired by Intergraph in 2002 (Smith)), is the GIS-based data collection environment for GeoMedia. ImageStation Stereo is able to capture, display and manipulate 3D photogrammetric and remote sensing data. It uses GeoMedia data servers to access common databases (e.g., Oracle Spatial, SQL Server or ArcSDE). Data collection is handled either interactively or facilitated by automatic attribution. Generated data can then be stored in an open database so that any GIS software can access it. Further, ImageStation Stereo supports compressed and uncompressed 8-bit greyscale and 24-bit rgb, jpeg and tiff formats. It offers dynamic zoom and automatic raster enhancement, interactive feature extraction and geometry validation capabilities as well as infrared shutter or passive stereoscopic viewing (Lemmens 2007). Dynamic zoom capability simulates the continuous optical zoom behaviour of a stereo plotter (Intergraph Product Sheet; Intergraph Users Guide). The integrated ImagePipe software enables stereo roaming. Intergraph markets this feature as a way of improving visualization performance for quickly navigating through stereo-displayed imagery (Intergraph Product Sheet). ImageStation Stereo supports 3D mice. 2.2.3 Earth Resources Data Analysis System (ERDAS)

ERDAS 3D Support. ERDAS Imagine is the raster graphics editor and remote sensing solution from ERDAS. Other solutions in photogrammetry

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and geographic information visualization fields include the Leica Photogrammetry Suite (LPS) (Francica 2008), Imagine Vector, ERDAS Image Compressor, ERDAS Virtual Explorer, ERDAS Imagine Stereo Analyst and ERDAS Imagine VirtualGIS. The last mentioned is able to create, analyze, and visualize 3D geographic representations. Users can project aerial or satellite images onto terrain models. They can add vector layers, symbols and 3D objects to the visualizations, create 3D animations and navigate through scenes. Using Imagine Developer's Toolkit, developers can implement applications in C and C++. In VirtualGIS the multi-resolution morphing feature provides seamless visualization during zooming operations. VirtualGIS supports raster formats (like img, gif, tiff), various DEM formats (from US Geological Survey (USGS), Digital Terrain Elevation Data (DTED), National Geospatial Intelligence Agency (NIMA) and Defense Mapping Agency (DMA)), Open-Flight databases and native DEMs of Imagine's OrthoBASE. In VirtualGIS it is possible to drape 3D raster and vector data. Aerial photography, satellite imagery, scanned maps and thematic images are typical raster data resources for such draping operations. Among vector formats ArcInfo coverages, shapefiles and Open 3D shapefiles are supported (ERDAS IMAGINE). ERDAS Stereo Support. Stereo Analyst – a product of Leica Geosystems – is the solution utilised in ERDAS Imagine for data collection, interactive analysis and visualization operations. Stereo Analyst superimposes existing 2D vector layers onto what Leica terms a “Digital Stereo Model”. These models can be created in four different ways: 1) Creating a relative stereo image pair by overlapping, leveling, and projecting corresponding images, 2) With the Create Stereo Model tool, which uses internal camera parameters and image information, 3) By using external aerial triangulation results from photogrammetric systems and 4) Via LPS which transforms raw data obtained from images to geospatial information for photogrammetric operations such as producing orthophotos, terrain models and extracting 3D features. Stereo Analyst supports anaglyphs, stereo emitters and stereo graphics cards. Image enhancement capabilities of Stereo Analyst include brightness and contrast adjustments, image histogram analysis, stretching and scaling operations. For efficient image processing and visualization hierarchical pyramids layers are used. In addition to Stereo Analyst, LPS Stereo is an add-on that can be combined with LPS or PRO600 (introduced in more detail in the section 2.2.5) for geospatial content extraction from stereoscopic images (Stereo Analyst for ERDAS IMAGINE). Stereo Analyst supports 3D mice.


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2.2.4 Autodesk AutoCAD

AutoCAD 3D Support. AutoCAD Map 3D is the solution of Autodesk built on the AutoCAD platform for creating, analyzing and managing 3D spatial information. Map 3D is able to drape aerial photographs onto topographic data and works with more than 4000 coordinate systems. Survey functionality, map creation, data integration and management, 3D surface creation (via the Surface Creation extension) and analysis (elevation, aspect and slope analysis) as well as shading studies and flythrough animations are offered, for example. Map 3D can visualize geographic objects depending on the viewer’s zoom level (i.e., LOD management for generalisation). Developers can further extend functionality by implementing applications using PHP, Java and .NET APIs provided by Autodesk. Map 3D is able to work with vector and raster data in several formats. Supporting open source Feature Data Object (FDO) technology, Map 3D extends data access for developers and supports ESRI shapefile, Oracle, Microsoft SQL Server, MySQL and ESRI ArcSDE. A large selection of raster formats (bmp, jpeg, jpeg2000, tiff, DEM, Portable Network Graphics (png), sid and ecw) are supported for streaming and visualization of multi-resolution images (AutoCAD). AutoCAD Stereo Support. In terms of stereoscopic visualization, Autodesk products employ one native and two external applications. LandXplorer is the 3D city modelling software of Autodesk. It can create, analyze and visualize digital city models. With dual head graphics card support, LandXplorer offers stereo viewing of digital models with shutter, polarised or anaglyph glasses. ELCOVISION 10 (developed by PhotoMess-Systeme) is one of the two third-party add-ons for Autodesk’s products. This close range photogrammetry package has several modes, which enable 2D digital rectification, stereoscopic measurements and stereoscopic visualization via anaglyph or shutter glasses (ELCOVISION). Super/Imposition (from DAT/EM Systems International) is the second external add-on. Super/Imposition is a graphics tool that allows stereoplotter operators to perform map revisions using digitised objects that are superimposed on stereoscopic models (Super/Imposition Product Description). DAT/EM supports 3D mice. 2.2.5 Bentley MicroStation

MicroStation 3D Support. Bentley Systems offers Bentley Descartes as a visualization tool integrated into its MicroStation software. Bentley Descartes can accomplish conversions between raster and vector data

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formats and between different coordinate systems. Bentley Descartes supports binary, greyscale and 1 to 64-bits colour images including, ecw, sid, img, jpeg2000, 1 to 32-bit tiff, rgb, and bmp formats. In addition to its tools which are able to crop, copy, move, merge, scale, mirror and rotate images, Bentley Descartes can create seamless mosaics of scanned aerial photos or raster images. It can also drape images onto digital terrain models (DTMs) or on 3D objects and apply lighting effects. Further, users can create fly-through animations and 3D PDF files as alternative means of visualization. Developers can use Bentley Descartes’ API to implement new functionalities (Bentley Descartes). MicroStation Stereo Support. The Leica PRO600 package (also known as ERDAS PRO600) is the stereoscopic feature collection and visualization tool used in Bentley MicroStation. Leica PRO600 provides a stereo viewing engine, data collection and editing tools as well as a feature definition library. It is closely integrated with LPS. Custom functionalities may be added via Visual Basic macros or C and C++ applications. The PRO600 package supports Leica TopoMouse and other 3D input devices and consists of several add-on modules, including PROCART, PROLPS, PRODTM, TerraModeller and LPS. These add-ons are responsible for cartographic functionalities, linking between modules, creation of workflows for terrain modeling applications, displaying DTMs and photogrammetric operations, respectively. PRO600 supports active and passive stereoscopic viewing (ERDAS Pro600). 2.2.6 Pitney Bowes MapInfo

MapInfo 3D Support. The Vertical Mapper module, integrated within MapInfo Professional, has map creation, analysis and 3D rendering features and mainly works on grid-based continuous spatial datasets. By means of the Grid Translator Pro (GTP) add-on from Geomatics Systems, Vertical Mapper can import around 60 raster formats (e.g., bmp, img, gif, jpeg, and Silicon Graphics Image (sgi)) to Vertical Mapper's grid format and export Vertical Mapper grids to standard raster formats. By means of the Preview Resolution option the degree of image resolution can be adjusted for the current view. Vertical Mapper features a Software Development Kit (SDK) which allows developers to implement additional functionality (Pitney Bowes). Encom, acquired by Pitney Bowes in December 2007, develops custom-built extensions for MapInfo Professional. One of these tools, Encom Engage 3D pro, handles 3D vector and raster data analysis and visualizations. To that end, Encom Engage 3D pro performs a number of tasks such as smoothing, clipping and analysis


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of spatial data, surface creation, application of transparency and lighting effects, creation of colour look-up tables, image format conversion and interactive presentation via fly-throughs. As an optional module of the add-on Encom Discover, Encom Discover 3D handles both 2D and 3D modelling and visualization, draping raster images onto 3D surfaces and real-time 3D navigation tasks (Encom Engage 3D; Encom Discover 3D). MapInfo Stereo Support. The Encom Discover 3D module supports dual-head graphics cards; therefore anaglyph viewing and full-colour 3D stereo projections are provided. For handling 3D navigation, 3D mice are supported (Encom Discover 3D). 2.2.7 GRASS and Quantum GIS

GRASS and Quantum GIS are open-source projects of the Open Source Geospatial Foundation (OSGeo) (OSGEO). Both are two commonly used open-source GIS. Since Quantum GIS uses some GRASS modules, their features are reported in the same section. Geographic Resources Analysis Support System (GRASS) 3D Support. GRASS is designed for management, analysis and visualization of spatial data, image processing, map production and modelling purposes. Users can either work with the graphical user interface (GUI) or a command line interface. There are over 300 core modules in addition to 100 add-on modules implemented in C, C++, Python, UNIX shell, Tcl or other scripting languages. GRASS has 2D and 3D raster and vector processing, visualization and animation modules. The Geospatial Data Abstraction Library (GDAL) is a translator library (licensed by OSGeo) for raster and vector spatial data formats (Quantum GIS). For example, the r.in.gdal module can be used to import a GDAL supported raster file (around 80 formats including tiff, bmp, jpeg, jpeg2000, gif, png, and sid) into a binary raster layer. The v.in.org module is used to convert GDALcompatible vector layers to a GRASS vector layer. The nviz animation and visualization module is used to visualize raster and vector data for rendering 3D surfaces and creating fly-through animations in the MPEG-1 video format. nviz has colour, lighting and transparency adjustment capabilities and provides control over resolution to improve rendering speed and to manage LOD. The tcl/tk interface is planned to be rewritten so that developers can add more functionality to the nviz module (Grass Documents).

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GRASS Stereo Support. In nviz anaglyph images can be created. Alternatively, Paraview, an opensource multiplatform data analysis and visualization application, can be used to render GRASS data in anaglyph mode (Grass Documents). Quantum GIS (QGIS). QGIS is a GIS under GNU General Public License (Quantum GIS). QGIS performs common GIS tasks such as editing, analyzing, composing and visualizing spatial data. QGIS allows users to develop customised GIS applications with the QGIS library using C++ or Python. Supported by GDAL, QGIS can handle numerous raster and vector data formats. The GRASS plug-in provides access to GRASS databases and to functionalities such as visualization of GRASS raster and vector layers, digitizing vector layers, editing vector attributes, creating new vector layers and analyzing GRASS 2D and 3D data. QGIS does LOD management by creating and storing lower resolution copies of data in an image pyramid. Depending on the zoom level, the most suitable layer of resolution can be selected from this pyramid. The Scale dependent rendering feature allows the user to specify a threshold for minimum and maximum scales at which a layer’s visibility is toggled. With the Map rendering option, the visibility of a layer can be temporarily suspended. There are sample workflows for QGIS users where 3D spatial data is created in LPS from stereo image pairs and GRASS plug-ins are used for visualization operations (ERDAS Inc.). Besides using the Grass modules, QGIS can handle stereoscopic visualization via a 3D Globe plug-in developed by Pirmi Kalberer (www.sourcepole.ch) and Marco Bernasocchi (www.bernawebdesign.ch). This plug-in is expected to become a standard in QGIS version 1.7. The 3D Globe is based on OpenSceneGraph and it supports 3D visualization as well as anaglyph and quad buffered active stereoscopic visualization (Walker 2010). 2.3 Synopsis The survey demonstrates that all of the analyzed software provide support for non-stereoscopic as well as stereoscopic 3D visualizations. For nonstereoscopic 3D, Intergraph is supported by the products of Skyline Software Systems, and QGIS makes use of GRASS modules. All other companies provide native non-stereoscopic 3D visualization solutions. In this category, Pitney Bowes provides two solutions: the native Vertical Mapper and the solutions from Encom, which has been acquired by Pitney Bowes. In stereoscopic visualization category, ESRI ArcScene, ERDAS Stereo Analyst and AutoDesk LandXplorer can be listed as native


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solutions. AutoDesk is also supported by external solutions from ELCOVISION and DAT/EM. Intergraph uses the solutions form Z/I Imaging and Pitney Bowes has support from Encom. ERDAS has a native solution, the Stereo Analyst, which is also used by ESRI. In this category, Bentley and QGIS are supported by external solutions. Bentley uses the P600 from Leica and Super/Imposition from DAT/EM. QGIS uses GRASS modules and OpenScene-Graph plug-ins. Table 1 collates the results of the software survey. The first column indicates the GIS software. The second column – 3D Support – reports the name of the corresponding native or external 3D visualization module. The third column – Stereo Support – lists the names of the stereoscopic visualization modules. In the fourth column, the respective supported stereoscopic viewing methods are listed as passive and/or active. Column five – Raster LOD – shows the supported raster LOD methods in the studied software. In 3D Support, 6 software have native 3D visualization solutions (ESRI, ERDAS, AutoDesk, Bentley, Pitney Bowes and Grass) and the remaining 2 utilize external implementations (Intergraph and Quantum GIS). In Stereo Support, 3 out of 8 GIS software are complemented by add-on products of the same company. Namely, Stereo Analyst (used by ESRI and ERDAS) and P600 (used by Bentley) are both products of Leica. This may indicate a possible common ground in approaches to, as well as methods in, stereoscopic visualization. As stated in the fourth column, 6 out of 8 software support both active and passive modes for viewing stereo and both open source software support only passive viewing. In Raster LOD, each software support multi-resolution raster representations of map layers. Additionally, the multi-resolution data format MrSID is supported by all software. The results show that leading commercial GIS software offer functionality that can handle non-stereoscopic and stereoscopic 3D visualizations, common forms of stereoscopic viewing and basic raster LOD management. However, they do not feature human visual system inspired LOD methods. It is worth noting that all software provide necessary operations to create, edit, and visualize 3D features. Raster and vector formats are supported by all products and many of them allow users to apply conversions between these. Furthermore, all studied GIS software can create fly-through animations and save these in various video formats.

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Table 1. Results of the GIS software survey (°: native solution, *: external solution).

3D Support ESRI

ArcGIS 3D Analyst°

Intergraph

TerraBuilder*, TerraExplorer*, TerraGate* ERDAS IMAGINE VirtualGIS°

ERDAS

AutoDesk

Stereo Support ArcScene° and Stereo Analyst* Imagestation Stereo° ERDAS IMAGINE Stereo Analyst°

Passive / Active Viewing Anaglyph, polarized / Stereo emitter, shutter glasses Passive system / Infrared emitter, shutter glasses Anaglyph, polarized / Stereo emitter, shutter glasses

Raster LOD Raster Pyramids, MrSID Imagery Layer, MrSID Multi Resolution Morphing, Hierarchical Pyramid Layers, MrSID Zoom Levels, MrSID

AutoCAD Map LandXplorer°, Anaglyph, 3D 2010° ELCOVISION10*polarized / Super/Imposition* Shutter glasses Bentley Bentley P600* and Anaglyph, LPS Image Descartes° Super/Imposition* polarized / Pyramids, Stereo emitter, MrSID shutter glasses Pitney Bowes VerticalMapper°,Encom Discover Anaglyph / Full- Preview Encom Engage 3D° color 3D stereo Resolution, 3D° and Discovprojection MrSID er 3D° GRASS nviz module° ppmtorgb3° and Anaglyph / – LOD, MrSID rgb3toppm° commands QGIS GRASS mod- GRASS modules Anaglyph, Scale ules and and OpenScene- polarized Dependent Graph plug-ins / Shutter glasses Rendering, OpenSceneGraph plug-ins MrSID


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3 Discussion and Conclusions The presented survey shows that all investigated commonly used GIS software provide non-stereoscopic and stereoscopic 3D visualization support either natively or by integrating a third-party software. The fact that all 8 software provide these services can be interpreted as meeting a demand from consumers, that is, companies clearly invest into either developing or acquiring 3D and/or stereoscopic visualization functionalities. Considering this together with the growing supply of stereo-enabled hardware in the market, makes it seem worthwhile to invest effort in developing more innovative 3D visualization approaches for GIS software and services. Both the demand and the tools are there, the functionality can still be improved upon. We will shortly highlight what we suppose such innovation should be aiming for. The results of our survey also clearly show that all investigated GIS software support stereoscopic viewing. However, the functionality is implemented to a different degree. While two open-source software (GRASS and QGIS) support only anaglyph (i.e., passive) viewing, all others support active stereoscopic viewing as well. This means they readily communicate with dual head graphics cards that can handle stereoscopic visualization. We interpret this as a positive trend of using efficient graphics processing and (effective) True 3D visualizations in geovirtual environments. Current raster LOD implementations in the selected GIS software (e.g., raster pyramids, hierarchical pyramid layers or MrSID format) focus on solutions for seamless zooming operations, accounting for distance or size controlled LOD (as explained in the section 1.4). While all surveyed software support multi-resolution graphics data, they do not include priority type or depth of field LOD management at all. Besides this shortcoming, there is the continuing growth of the GIS user-base, virtual globes and online mapping services and the increased availability of larger datasets. Some virtual globes not only offer 3D visualization but also stereoscopic viewing through a third-party software (e.g., TriDef for Google Earth). This can be seen as a further indication of the increasing interest of both professionals and laypersons in True 3D visualizations. However, it is also worth to mention that virtual globes and online mapping services are frequently hindered by bandwidth limitations. Therefore, exploring alternative LOD management techniques may not only be helpful for full-blown desktop GIS but also for over-coming some of the inherent limitations of online 3D geovisualization services.

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We thus identify a need to further improvement of LOD management approaches. We think that by introducing human visual system inspired LOD management methods into existing GIS software and services, the 3D visualization experience could be substantially enhanced. Improvements may include (but are not limited to) extending the use of LOD management models and methods, representing spatial data in a more effective and efficient way and finding solutions that may reduce the complexity of cartographic visualizations. In 2002, Heipke pointed out that, while modern GIS software should contain modules supporting all stages of handling 3D features, they are rather far away from providing this support (Heipke 2004). The survey results suggest that today’s GIS software have indeed come a long way and are now equipped with modules which can deal with 3D geo-spatial graphics. Additionally, most of the software provide comparable capabilities (i.e., supporting 3D and stereoscopic visualization, supporting dual head graphic cards) in terms of spatial data handling and visualization. How well these modules function in real-world scenarios will be the subject of a follow-up study. In order to support and complement the information obtained from this software survey we meanwhile launched an online questionnaire (however, analysis has not been finalised at the time of this writing). The main objective of the online questionnaire is to measure the attitudes and opinions of experts working in GIScience towards 3D and stereoscopic visualizations. Early results indicate that a majority of the participants make use of 3D or stereoscopic 3D for analyzing and visualizing geographic information. A detailed analysis from that questionnaire will be included in a follow-up publication.

Acknowledgements This research is funded by SNF project “GeoF: Development and implementation of Geofoveation” 200021_120434/1. We would like to express our gratitude to the company representatives who have made the time to speak to us about their products as well as Dr. Frank Ostermann and Marco Bernasocchi for their input to improve this manuscript.


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Think Differently: a New Method to Create Lenticular- and Integral-Pictures

Dirk Stendel Berlin University of Technology, Berlin, Germany

Abstract The lenticular technique is an autostereoscopic presentation technique based on two cooperating components - a lenticular plate and a lenticular base picture underneath it. Both have to be adjusted very precisely in order to reconstruct a visible picture with a spatial impact on the observer. In the middle of the 1970s the interlace-method was established as a standard procedure for the generation of lenticular base pictures. During the past 15 to 20 years complementary methods have been developed based on the advance in computer technology. The traditional concept of handling the half images, as used with basically every other stereoscopic presentation technique, was given up: all of the half cylinder lenses on a lenticular plate are supplied with individually adjusted base images. This new approach and methodical changes permits in the further development a great potential for the improvement of the visible quality of spatial images and of the lenticular hardware itself. The up to now welldefined and uniform surfaces of the lenticular plates may now be diversified for more flexibility. This paper will present different techniques regarding this development. The focus will be put on the VLR method (virtual lenticular renderingmethod), which creates new spatial image attributes an qualities, e.g. a considerably expanded viewing area in front of the autostereogram, the improved display of outlines of the objects and the automated coding of motion parallaxes. M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_4, © Springer-Verlag Berlin Heidelberg 2012

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Dirk Stendel

The mentioned methods generally work as well with „Fly’s-Eye” circular or comb shaped singular lenses of a lenticular plate. This fact creates additional potential for autostereoscopic and especially paper based 3D-presentations in a scientific context. This paper covers as well the question, to what extent the VLR method already may be used in the context of a planning discipline and how different user groups react towards the new visible picture qualities. The results will show that such methods as the VLR method are better qualified in the planning context than the Interlace-method. Based thereupon, it could significantly support the establishment of a new autostereoscopic presentation standard in the planning sciences. Keywords: 3D-visualization, autostereoscopic picture, lenticular picture, evaluation, integral imaging, VLR method

1 Introduction Although the lenticular technique is based on a balanced cooperation of the lenticular plate and the lenticular base image, in the authors opinion the impact of the base image is underestimated. At present, the mode of operation of a lenticular plate is described and predominantly analysed in a paraxial way. Paraxial meaning, that the light refracting processes, e.g. in a half cylinder lens, are described with parallel or nearly parallel light beams regarding to the optical axis of the system observed. A paraxial approach causes a simplification in analysis. The classification of a lenticular plate by the parameters focal point (F), central axis (H) or central point beam may not explain sufficiently all occurring optical phenomena, like spherical aberration, caustic or coma (cf. Haferkorn, 2003, Schröder and Treiber, 2002). On the one hand this has a specific effect on the construction of the lenticular plate and on the other hand on the aligned lenticular image underneath it. The lenticular plate is primarily used for an exact half image separation. The concentrated use of the Interlace-method since the 1970s (Roberts, 2003) seems to be proof of the optimised adjustment of both system components. The Interlace-method generates an interlaced image on the base of two (stereogram) or more (panoramagram) half images. The more half images are being used, the wider the viewing range of the visible spatial image and the better the overall quality will be (Okoshi, 1976, Halle, 1997). The created image displays the sectioned information of the

Think Differently: a New Method to Create Lenticular- and IntegralPictures 69

half images according to the exact focussing of light beams at the base of the lenticular plate (Fig.1). The use of the Interlace-method was up to now enhanced by the fact that within the field of stereography and stereoscopy methods are established which creates stereograms and panoramagrams regularly based on half images.

Fig. 1: Construction principle of a lenticular plate The half cylinder lenses of the lenticular plate to generate a spatial effect are constructed to exactly focus parallel light beams on the base of the lenses (in: Okoshi, 1976).

With the Interlace-method the half images are sectioned into stripes and accurately placed beneath a half cylinder lens. In the end of the process they are all combined to a composite-image. The number of stripes underneath each lens is correlated with the amount of half images being processed (cf. Bourke, 1999a, Bourke, 1999b, Bourke, 2003). Due to this method of operation major restrictions exist regarding the quality of the spatial image and the range of possible viewpoints when facing a lenticular image. In the planning context, especially with related presentation formats (e.g. DIN A0), these disadvantages become apparent. The practical use of large-sized lenticular images therefore up to now required a lot of resources (cf. Buchroithner, 2007).

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Fig. 2: Photograph of a lenticular image (Interlace-method, enlarged) The birds stepped outline shows clearly a typical display effect of the lenticular technique. It is also known as sampling effect (in: Rath, 1993).

Figure 2 and Figure 3 show the essential impairments caused by the Interlace-method as perceived by the author: the limited accuracy of displaying outlines of 3D-objects (Fig. 2) and the constriction of the viewing range in front of the autostereogram (Fig. 3). Object outlines and their visual quality are very important in the planning context due to subject-specific requirements. The human vision is provided with helpful information for the spatial comprehension (Goldstein, 2002, Mallot, 1998). Stepped object outlines (Fig. 2) may not be avoided with the Interlace-method. Apart from that they are influenced by the single-lens-construction (sampling effect).

Fig. 3: Viewing range in front of a lenticular image (display)

Think Differently: a New Method to Create Lenticular- and IntegralPictures 71 The illustration shows discrete viewing zones allocated either to the left or the right eye in front of a lenticular image. Depending on the viewers position, an orthoscopic (50 percent) or pseudoscopic image may be generated. The pseudoscopic view produces an inaccurate image. (in: Dodgson, 2006, Dodgson et al., 1999)

An enlarged and wider viewing range (than shown in Fig. 3) is of importance for multi-user purposes. The simultaneous viewing and discussing of the presented contents is subject-specific, of major importance and should be promoted. As many participants as possible should be able to simultaneously contemplate an accurate image. As Figure 3 shows, at present this is not possible.

2 New methodological Strategies Room for improvement of the viewing conditions and the visual spatial image quality is limited with the Interlace-method. The processing of a greater amount of half images as well as smaller half cylinder lenses are possible parameters for improvement. Structural constraint of the technique itself of course may not be resolved. Three different methods are presented in the following, which uses varying modes of operation for creating the base image and consequently provide different measures of influence on the spatial image quality. The traditional way of processing the half images was given up. Mainly affected by the integral photography (by G. Lippmann, 1908), optical systems have been developed which create accurately fitting base images. As in integral photography, generally more than one exposure is necessary (cf. Dudnikov, 1970, Dudnikov, 1971). Accurately fitting in this context means with respect to the decoding capacities of a lenticular plate (each single half lens) and the possibility to compensate effects like the spherical aberration. This development in methods is explicitly linked to the continued improvement of performance of computer hardware and graphical software the past 15 to 20 years (Stern and Javidi, 2006). Now it is possible to virtually display complex optical systems and therewith create base images (ray-tracing). On top of that it is possible to develop optical systems, which could not be constructed without major effort in real-life. Planning sciences nowadays typically utilize 3D-computer models, therefore those methods seem to be most promising which have a virtual mode of operation and may be incorporated in the 3D-model. The method

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by Terlutter, the Integral Imaging System by Davies & McCormick and the VLR method (virtual lenticular rendering method) are presented. All of these methods create images equipped with disparity parallaxes and motion parallaxes. Because of that the visible images provide a comparatively stable spatial impact. Depending on the method, the motion margin in front of the autostereogram varies, but is noticeably improved compared to the Interlace-method. The VLR method has already been tested for utilizability and applicability (see part 3). 2.1 Method by Terlutter With the Interlace-method, the half images used for stereograms and panoramagrams are processed uniformly. The image content of the autostereogram is – independent of their further purpose – only determined by the stereographic exposure specifications. R. Terlutter reversed these dependencies. His method starts up from the point of view of the observer and not from the stereographic exposure situation. The half image production is directly linked to the observers eye position. Figure 4a illustrates the mode of operation schematically. Depending on the intended lateral motion range, two different half images are recorded. In the following, the half images are overlaid and filtered according to the measures of a certain lenticular plate and with regard to varying observer positions. A base image is created by the numerous or rare display of a certain object point depending on the relative position of the object in space. Figure 4b shows the concluding result: a parallaxpanoramagram. Unlike the Interlace-method, a selective, distancedependent and viewpoint-optimised recording of 3D-object information is possible with the method by Terlutter (Terlutter, 1997).

Fig. 4a: Variation of view directions

Fig. 4b: Parallax-panoramagram

Think Differently: a New Method to Create Lenticular- and IntegralPictures 73 Both illustrations show the observer-oriented method by Terlutter. The half images are filtered with respect to the parameters of the lenticular plate and the intended viewpoints on the observer. The result is a parallax-panoramagram (in: Terlutter, 1997).

2.2 Method by Davies & McCormick This computerbased technique – Integral Imaging (II) – uses five different lenticular arrays as optical coding systems according to integral photography. Supported by this complex system a virtual 3D-object is directly recordable as a lenticular base image on the 2D-image plane (Davies et al., 1988, Stern and Javidi, 2006). Figure 5a illustrates the developed system consisting of macrolens and microlens arrays. First of all, a virtual pseudoscopic image is generated via a so called “Double Integral Screen”. This image is then recorded on a virtual 2D-image plane with another microlens array. If a real-life lenticular plate, corresponding to the microlens array, is then positioned in front of the created base image (integral image) a completely orthoscopic spatial image becomes visible. The impact of this autostereogram is nearly independent of the viewing distance and viewing position (Milnthorpe et al., 2003).

Fig. 5a: Integral imaging camera The illustration shows an array of lenticular plates used for the coding of a integral image (in: Milnthorpe et al., 2003).

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Fig. 5b: Location of the visible 3D-object in space The illustration shows the reproduction position of a 3D- object coded in Figure 5a. The object may show before and beyond an image plane (in: Milnthorpe et al., 2003).

Figure 5b illustrates the reconstruction of a 3D-object and its spatial reproduction positions on a screen plane. Depending on the position of the pseudoscopic image in the virtual model, the location of the spatial image changes. The virtual realisation of the optical coding system made it possible to combine the whole process in a 3D-camera. The Integral-imaging-camera (II camera) is very complex though and not yet suitable for everyday use respective real-time use (Milnthorpe et al., 2003). Used in a display presentation context, the visible resolution of the stereograms is comparatively low. 2.3 The VLR method The VLR method is an integral image technique as well but of comparingly low complexity. Instead of a high number of different lenticular plates the optical system of this technique is reduced to a single coding lenticular plate. Figure 6a illustrates the coding process schematically. In contrast to the method of Davies & McCormick a regular scene camera is used as a recording agent in the 3D-model. Therefore, even perspective images may be realised with a high accuracy of position.


Fig. 6a: Coding procedure of the VLR method A virtual lenticular surface is used to encode several 3D-objects in a 3D-scene. A traditional 3D-scene-camera is used. The recording of isometric images is possible dependent on the camera setting/calibration. As an overall balancing parameter the surface refraction index is introduced (Stendel, 2008, Stendel, 2009).

Using the VLR method, the extent of the 3D-scene, the position of the camera and of the coding surface have to be considered. A mathematical model was developed which uses the refraction index of the coding surface as a balancing parameter and adjustment parameter respectively. Figure 6b shows a photograph of a spatial image reconstructed by a 10 lpi (lens per inch) lenticular plate (left) and the corresponding base image generated with the VLR method (right).

Fig. 6b: Photograph of a spatial image (left) and the corresponding base image generated with the VLR method (right) The illustration shows a photograph of a spatial image (ground view) and the corresponding base image, generated with the VLR method. Compared to Figure 2, differences in the outline quality show clearly. (See colour image in

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appendix)

At present, only spatial images may be generated with the VLR method that are displayed behind the displaying image plane. This limitation seems to be acceptable in the field of business context. In the field of stereoscopy it is partly demanded explicitly (Waack, 1982). Unlike the other methods presented in this paper, restrictions of the VLR method related to the visible image resolution may be effectively compensated for by a high resolution print (600 dpi in Fig. 6b). Automation of the process is not achieved yet. The application of half cylinder not focussing on the base of the lens but considerably behind it leads to an improved stereogram quality. Compared to the standard mode of operation, a fourfold to sixfold increase of visible resolution is possible, dependent to the used lens size and their focal characteristics.

3 VLR method - some evaluation results The VLR method was tested practically in the field of planning sciences in the context of a DFG (Deutsche Forschungsgemeinschaft) co-financed research project (Tauglichkeit der Lentikulartechnik für Planungswissenschaften am Beispiel der Landschaftsarchitektur). To what extent are the benefits of this autostereoscopic illustration method appreciated? How do different user groups react to the technique? Issues like these were surveyed subject-specifically in the field of landscape architecture. Despite the early stage of development of the VLR method, significant first conclusions may be drawn. The basic hypothesis of the project was that this illustration technique may be very useful for subject-specific presentations due to its improved and customised spatial image quality. A survey of 119 people of different professional backgrounds and expertise was conducted. The given answers were analysed. The evaluation of the assessed data regarding the lenticular images presented can hardly be separated from effects of the base image production process. The presentable stereogram quality is method-specific. Therefore the presented results directly relate to the VLR method but not to lenticular images in general. However, a trend of applicability shows by the means of the survey structure and focus of analysis (spatial image quality).


3.1 General Tendencies The final question of principle of the survey was “Concluding, which presentation technique would you prefer for your own visualizations and presentations? 3D or 2D? . The results are shown in Figure 7. “

Fig. 7: Survey results on acceptance or rejection of lenticular images generated with the VLR method

43,7 percent directly approved of a 3D presentation technique (VLR method) in the field of business. In the reverse conclusion, 56,3 percent of the interviewees preferred the traditional 2D-design. Further differentiation leads to the following conclusions. Only 31,1 percent voted for 2D directly and therefore actively disapproved of the 3D technique. 25,2 percent of the interviewees voted for 2D due to the “complex production process”, “high costs” and “current image quality”. In case of further development and an improved mode of operation of the VLR method, these doubts may be overcome. Differences in the results with regard to user groups became apparent as well. Laymen and professionals with a focus on visualization showed a twofold higher acceptance of this presentation technique than any other user group. The interviewees themselves attributed the applicability and added-value of the lenticular technique to the addressed user group. 3.2 Detailed Results More than 82 percent of the interviewees acknowledge a general and positive difference between 2D- and 3D-images. 3D-illustrations appear “more lively” etc. About 56 percent attest an increased comprehensibility and unambiguousness of the presented contents compared to 2D-

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illustrations. More than 50 percent experienced an “obvious” to “very obvious” spatial depth in the images, even though the actual visible spatial depth in the presented pictures did not exceed 2,0 cm to 2,5cm. 70 percent sensed the spatial effect as not distinctive enough. The visible image resolution was rated below average and was generally compared to the 2D-quality. Subject-specific typical image resolutions of 150-230 dpi for DIN A0 images may not be realised by the VLR method at present. The visible image resolution is reduced to about 20 percent of the original resolution of the base image by the sampling-effect and by the use of an animation lens array. The visible resolution of the presented posters therefore amounted to not more than 50 dpi, which puts the evaluation outcome into perspective. However, small lettering in the posters could be easily read and was clearly positioned in space. Considering the technical development in the fields of printing technology and computing power, lenticular images with a conventional resolution may be produced. Potential professional fields of application mentioned by the interviewees were graphically demanding occasions like competitions, exhibitions and formal presentations. Above average results occurred for “exhibitions” throughout all user groups. User specific differences in the evaluation results show clearly. These results all together suggest no general scepticism towards the lenticular technique based on the VLR method. A general acceptance may be noted and may, in the author’s opinion, be closely related to the traditional presentation medium paper. It is unknown so far, whether these results would be achieved as well with a digital presentation of the lenticular technique. Further studies are necessary. The automation and integration of the VLR method in common 3Dsoftware might further increase the general acceptance. Current constraints due to the complex processing will be significantly reduced. Examples of an easy-to-handle implementation already exist as described by Davies & McCormick. This could be optimised by combination with a so called “light field rendering” (Isaksen et al., 2000).

4 Outlook - Conclusion The evaluation outcome as well as the expected development of lenticular plate technology and software improvements support autostereoscopic visualization techniques as a possible new presentation standard in planning sciences for the future. The advantages regarding communication of content and graphical unambiguousness are obvious. No other than the


lenticular technique seems to be able to perform so well subjectspecifically. The differing planning sciences (architecture, urban planning, transport planning, cartography etc.) all have very similar illustration requirements. Therefore the evaluation results presented in this paper are transferable.

Fig. 8: Completely parallax lenticular base images generated with the VLR method (cf. Fig. 6b)

Figure 8 shows a lenticular base image of a virtual cube generated with the VLR method using a surface of round half lenses (Fly’s-Eye lens array). Completely parallax panoramagrams could lead to a further improvement of the visible attributes of autostereograms and consequently lead to an even higher applicability of them in the field of business. The utilisation of circular lenses for instance would make the perpendicular viewing of lenticular images unnecessary. Vertical aberrations may presumably be compensated for. For lack of according lenticular plates (lens sizes of 3 to 40 lpi) an implementation is impossible at present. Experiments with simple lenticular structured form-glass have already been conducted successfully but are limited by the available optical quality. Multidisciplinary research projects are needed in order to further develop the technique subject-specifically. Hardware as well as software development need to be closely interconnected. The conceptual foundation for such an advancement already exists.

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5 References Bourke, P. (1999a) Autostereoscopic lenticular images. online published at: http://local.wasp.uwa.edu.au/~pbourke/projection/lenticular/ Bourke, P. (1999b) Calculating Stereo Pairs. online published at: http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/stereorender/ Bourke, P. (2003) Creating stereoscopic images that are easy on the eyes. online published at: http://local.wasp.uwa.edu.au/ ~pbourke/miscellaneous/stereorender/ Buchroithner, M. (2007) Echtdreidimensionalität in der Kartographie. Kartographische Nachrichten; Fachzeitschrift für Geoinformation und Visualisierung, 57, 239-248. Davies, N., McCormick, M. & Yang, L. (1988) Three-dimensional imaging systems: a new development. Applied Optics, 27, 4520-4528. Dodgson, N. A. (2006) On the number of views required for head-tracked autostereoscopic display. "Stereoscopic Displays and Applications XVII". San Jose, California, 16.-19. Januar, SPIE 6055. online published at: http://www.cl.cam.ac.uk/~nad10/pubs/SPIE06.pdf Dodgson, N. A., Moore, J. R. & Lang, S. R. (1999) Multi-view autostereoscopic 3D display. IBC '99 (International Broadcasting Convention). Amsterdam. 10.-14. September. online published at: http://www.cl.cam.ac.uk/~nad10/pubs/IBC99-Dodgson.pdf Dudnikov, Y. A. (1970) Autostereoscopy and Integral Photography. Optical Technology, 37, 422-426. Dudnikov, Y. A. (1971) Elimination of Image Pseudoscopy in Integral Photography. Optical Technology, 38, 140-143. Goldstein, E. B. (2002) Wahrnehmungspsychologie, Heidelberg; Berlin, Spektrum, Akad. Verlag. Haferkorn, H. (2003) Optik - physikalisch-technische Grundlagen und Anwendungen, Weinheim, Wiley-VCH Verlag. Halle, M. (1997) Autostereoskopic displays and computer graphics. Computer Graphics 31, 58-62. Isaksen, A., Mcmillan, L. & Gortler, S. (2000) Dynamically Reparameterized Light Fields. 27th International Conference on Computer Graphics and Interactive Techniques. New Orleans, ACM SIGGRAPH. online published at: http://groups.csail.mit.edu/ graphics/pubs/siggraph2000_drlf.pdf Mallot, H. A. (1998) Sehen und die Verarbeitung visueller Informationen, Wiesbaden, Vieweg Verlag. Milnthorpe, G., McCormick, M., Aggoun, A., Davies, N. & Forman, M. (2003) Computer generated Content for 3D TV Displays. De Montfort University (UK). online published at: http://www.broadcastpapers.com/whitepapers/IBCDeMontfortCGContentfor3 DTV.pdf Okoshi, T. (1976) Three-dimensional imaging techniques, New York, Academic Press.

Think Differently: a New Method to Create Lenticular- and IntegralPictures 81 Rath, W. (1993) Bilder in 3 Dimensionen - Linsenrasterverfahren. online published at: http://www.hobby-output.info/bilder_3d/ linsenraster/linsenraster.htm Roberts, E. (2003) History of Lenticular and Related Autostereoscopic Methods. Leap Technologies. online published at: http://www.microlens.com/pdfs/history_of_lenticular.pdf Schröder, G. & Treiber, H. (2002) Technische Optik, Würzburg, Vogel Verlag. Stendel, D. (2008) Autostereoscopic Visualization of Landscape. In Buhmann, E. (Ed.) Digital design in landscape architecture 2008. Heidelberg, Wichmann. Stendel, D. (2009) Autostereoscopic Visualization of Landscape - a Research Project. In Schrenk, M., Popovich, V. V., Engelke, D. & Elisei, P. (Eds.) CORP 2009- Competence Center for Urban and Regional Development. Sitges, TU Wien. online published at: http://www.corp.at/ Stern, A. & Javidi, B. (2006) Three-Dimensional Image Sensing, Visualization, and Processing Using Integral Imaging. IEEE, 94, 591-607. TERLUTTER, R. (1997) Verfahren zum erzeugen räumlich wirkender Bilder. Europäisches Patentamt. EP 0 760 145 B1, Deutschland. EP 0 760 145 B1, DeutschlandWaack, F. G. (1982) Stereographie: Einführung in die Fototechnik und praktische Ratschläge für die Aufnahme, Berlin, Selbstverlag.

Truly modelling reality…? – Let’s improve our cognitive maps with a bastard mix of algorithms to “undo” pictures, isometric mapping, highdensity diagrams and comic culture as integral sign posts for software development in cartography

Niels-Christian Fritsche

Institute of Foundations of Design and Architectural Delineation, Dresden University of Technology, Dresden, Germany

Abstract Throughout the history of man, a distinction has been made between 2d drawings and 3d models. The rift extends into art forms and software families. Prospective cartographic tools will have to provide fluent navigation between two- and three-dimensional data on top of their native software branches. The tools will have to use a bastard mix of projection forms, information displays and customization features. I suggest a revival of isometric projection to provide a bridge between maps and models, the cultivation of high-density diagrams to convey complex data and the rediscovery of the comic art to narrate complex stories in relation to the “augmented reality” cartography always has constituted. Keywords: Augmented reality, Data-ink ratio, High-density diagrams, Isometric mapping, Reality, Representation, Stereoscopy


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1 Truly modelling reality? “True 3d in Cartography” poses a fundamental question: Can something other than reality itself ever become “true 3d”? – Cartography maps reality. Therefore there has to be a difference between the reality and the depiction of it. But what is reality? Ancient philosophy painted reality as an illusion. Parmenides, in the 5th century BCE, considered the outside world of appearances false and deceitful. For him the world was composed of ideas. When ancient cartographers started to map their worlds they included religious and artistic ideas. While Parmenides’ position is quoted in artistic views today (“There has to be a truth beyond what can be seen”), contemporary cartography is defined as the science and the practice of making geographical maps and models. A map, as a visual representation of a territory, purports to represent the viewable as correctly as possible. By aiming at the ultimate map-territory relation, cartography grazes the philosophical debate about reality and representation.1 The map has to represent the territory, and yet cannot become a copy of it. Jorge Luis Borges’ metaphor about the “Exactitude in Science” applies: “...the Art of Cartography attained such Perfection that the map of a single Province occupied the entirety of a City and the map of the Empire, the entirety of a Province.”2 Cartography succumbs to the notion of a visible reality and subjects itself to the meticulous mapping of the visible – thus the urge to be as “real” and “true 3d” as possible. New car navigation systems and 3d moving pictures pledge that cartography can map the viewable appearance of the real world virtually realistically. Although we still struggle to bindingly define the term “virtual,” it is generally regarded as “that which is not real” but which displays the salient qualities of the real. Nevertheless, Augmented Reality (AR) and the “Outernet” (Torsten Rehder) point rather into a hybrid, loaded experience of reality than a real or virtual copy of it. The buzzword “augmented reality” characterizes semantic additions to the real-time representation of the environment, thus reviving what cartography has always done: adding words to a map. The “Outernet” allows reading real tags in reality and links real objects to additional information: “Things learn to speak” in reality, not just on a cartographic map or a model.3 Putnam (1992), pp 61-71, asks: “Are there such things as reference and truth?” and discusses “truth as a property.” 2 Borges JL (1935) A Universal History of Infamy. Quoted after (1998) Collected Fictions. Viking Penguin, New York NY, p. 325 3 Becker T (2010) Outernet. Die Welt wird zur Webseite (in German). KulturSpiegel 1; 12 1

Truly modelling reality…? – Let’s improve our cognitive maps with a bastard mix of algorithms to “undo” pictures, isometric mapping, high-density diagrams and comic culture as integral sign posts for software development in cartography 85

Applying Parmenides’ world of ideas and Borges’ exactitude in science to contemporary cartography, a computer model of melting glaciers could be issued as a animation of the glacier’s retreat to show what is “really” going on, it could print out the decline of the glacier in the plain numbers of the “real” losses, it could diagrammatically relate the glacier’s retreat to weather data and the carbon dioxide concentration to “really” interpret the phenomenon, and it could simply issue spoken command lines such as, “Reduce beef consumption to decrease methane emissions from cows” to “really” do something about the retreat phenomenon. Consequentially, a “true 3d” car navigation system does not need a separate screen. It should suggest semantic additions to the real-time experience of the environment – as cartography has always done and what “augmented reality” is all about – as projection of visible and audible data, admonition and directional advice, into the cockpit, the windshield, and/or as a direct stimulus to the driver’s retinas.

2 Stereoscopy and/or “true 3d” The conference on “true 3d in cartography” intends to “cover all aspects of (auto-) stereoscopic representations.” Stereoscopy refers to the illusion of depth created by presenting a slightly different image to each eye. In reality, the stereoscopic business affects the foreground of our binocular vision only – our immediate range of action. That foreground extends to a range of ten to thirty feet, beyond which – as can be observed by closing one or the other eye –the binocular disparity disappears. We have to rule out that stereoscopic vision equals “true 3d” on the cartographic scale. However, stereoscopic vision can be successfully applied to haptic and non-haptic cartographic representations – by tricking the neurons responsible to decipher the signals from the retinas of both eyes by providing them disparity computed images. Naturally, real territories do not fit the foreground of our stereoscopic vision. Yet haptic cartographic representations like maps, lenticular foils, millwork scale models or raised-relief globes do.4 But are these representations – regardless of how detailed and “real”-looking – “true 3d”? Haptic representations have to be considered “true 3d” insofar as they represent the three dimensions accurately, if only up to scale. They are not to be confused with “true 3d” because they do not relate to the real expe4

http://kartographie.geo.tu-dresden.de/true3Dincartography09. Conference topics.

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rience. A millwork scale model of a mountain range, for instance, shows the spatiality of the relief to an extent a helicopter pilot with a flying altitude of – let’s say – 500 feet would not be able to enjoy. Perhaps this explains the fascination for miniaturizing things – we suddenly see hyperrealistic model railway territories with tremendous stereoscopic spatiality. Jean Baudrillard remarked on the “paradoxical” counter-movement to the “Promethean expansion” to occupy the whole world: “Freed now from the need to refer to the human scale, to the life-size,’ [...] mechanisms tend increasingly [...] towards the quintessential microcosmic.”5 If we dismiss that non-haptic representations are not 3d because they are presented on flat screens then we also have to consider them “true 3d” since stereoscopic enhancements by disparity computed images can, potentially, encompass the entire depth range, from the immediate foreground to the distant silhouettes. Film or TV screens are within reach; thus disparity computation appears to be the tool at hand. Regardless that binocular disparity for stereoscopic vision can be calculated for everything visible: in doing so it creates the illusionary offset in depth that exceeds depth perception in the real world and, therefore, should not be considered “true 3d.” Currently the industry promotes 3d movies and 3d TV with a thorough amplification of depth effects – like a stack of lenticular foils. But how “real” is it to stereoscopically differentiate monocular cues like aerial perspective, accommodation and peripheral vision of a distant mountain range? It remains to be seen whether and how 3d moving pictures persist to be effect-driven or if 3d will lead to intensified plots with “3d stories,” new tactical levels of camera work, image composition and film editing. So far the industry is heading for event-driven formats like sportscasts and action movies with stereoscopic close-ups applicable to the binocular vision and an emphasis on the rather monocular motion parallax. No matter how “realistic” stereoscopy and “true 3d” applications will become: Let’s be reminded that true representations of reality, which the arts have aimed at throughout their history, ever since Pliny the Elder’s “Naturalis Historica” and the story of Zeuxis’ painting of grapes, which successfully seduced birds, often fall into the gap between initial admiration of the Trompe-d'oeil and the subsequent revulsion when recognizing the hyper-real as a hoax, something Masahiro Mori came to call “the uncanny valley” for the interaction between humans and robots.6 ’

5 6

Baudrillard (1996), p. 51 Mori, M (1970) Bukimi no tani. The uncanny valley (K. F. MacDorman & T. Minato, Trans.). Energy, 7(4), 33–35. (Originally in Japanese.)


3 Images: frame, distance and movement We are visual beings; images seem to be unavoidable. Notwithstanding, one of the most striking achievements of mankind is the capacity to develop abstract ideas, to develop an urge to depict such ideas and to depict these ideas on a surface. The profane cave drawing and the religious icon both succeeded in putting importance on a surface. The curious look on an object made and imbued with meaning by humans became one of the most convincing success stories in the history of man. Anne Friedberg makes a strong, convincing case that the entire history of visual depiction is bound not only to the selection of worthy images but also to the need to frame them.7 Leon Battista Alberti, as early as 1452, compared the frame of a painting to an open window (“aperta finestra”). Martin Heidegger formulated an ontological cut, referring to human perception, in which something of importance is isolated against the rather unimportant background.8 Next to just any image of importance the “true” depiction of depth became the natural focus or artistry. The invention of the single-point perspective by Renaissance artists has generally been considered one of the most important turning points in the arts. Suddenly there it was: the third dimension, depth, accurately depicted on a flat surface. When the cinematic century arrived, most viewers did not notice that the revolution, literally, took place within the frame of flat images full of spatial indications. It did not matter that the quality of the early projections clearly exhibited a black-and-white, low-resolution appearance that was not to be confused with reality; the observers were already used to taking spatial indications for the real thing. The “true” depiction of spatial depth in a picture frame naturally translated to moving pictures in a picture frame, to the computer screen with various windows, to the Virtual Reality (VR) of computer-generated imagery, and to the AR we are interested in today.9 Since we are so used to the fixed frame of moving images, the acceptance of realistic demonstrations of the real world as an image, a film or a computer screen becomes a “natural given” to us. We honestly consider a flat image or a flat screen with spatial indicators as “spatial” even though it Friedberg (2006) p. 43 (perspective), p. 93 (moving image), p. 174 (film screen), p. 232 (computer screen) 8 Heidegger M (1996) Being and Time. State University of New York, Albany 9 Friedberg (2006) p. 243 7

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physically is not. Evolutionary, we became keen handlers of spatial indicators like the size change of objects, changing overlaps of objects and changing density gradients. Spatial experience was bound to a number of computational tasks, and based on movement in space. It is not only triggered by a variety of environmental sensations like sounds, smell and temperature, but the bodily feedback of ones own movement. We realized space by realizing that we are moving through it. Recently, we started to fool ourselves successfully by training and tricking our neurons for and into viewable indications of spatiality. Our eyes, of course, only compute what they are shown. Our brains, nevertheless, have learned to be more rational than to trust just any incoming set of sense data.10 With stereoscopy as an all-purpose tool we may even develop a false sense of handiness when it comes to estimating distances and extensions. Current VR environments already include some sensory information, like sound and tactile stimulus such as force feedback. These raise serious anthropologic concerns. Kids, after extensive exposure to wide-angle video games, tend to miscalculate distances in real life. This concern used to be of lesser urgency when it came to non-haptic representations. Now, a digital native may dangerously confuse haptic and non-haptic representations with reality.

4 The rule of cartographic economics With Global Positioning System (GPS)-based cartographic tools the mapterritory relation is reconnected to the “Outernet” territory. With a number of formerly oppositional interests – scientific curiosity, military secrecy and entrepreneurial spirit – collapsing in one frame, educational and recreational aspects merge also. And so do their respective drives for results. The question, “What do we want?” used to be answered by the predominant agenda at hand. Technological advancement, after all, never was entirely demand-driven but “puritan” (Max Weber),11 “ideological” (Arnold Gehlen)12 and “positivist” (Herbert Marcuse). 13 Computerization constituted a unique selling proposition as long it was an unevenly spread development. With the advent of “ubiquitous computKandel et al. (1981) Weber M (1930) The Protestant Ethic and the Spirit of Capitalism. Charles Scribner‟s Sons, New York NY 12 Gehlen A (1989) Man in the Age of Technology. Columbia University Press, New York, NY 13 Marcuse H (1964) One-Dimensional Man. Beacon, Boston 10 11


ing” (Mark Weiser) – computation being everywhere, inside and outside our houses, and even our bodies – this selling position ceases to be fundamental. Concurrently, the publicly accessible abundance of geodata has to be reformatted for explicit assertions about scientific and commercial queries. It becomes about time to propose new rules of cartographic interfaces to relay comprehensible message structures on top of massive amounts of data. Generalization has always been the concern of cartography. Now the concern could sound like Edward Tufte’s famous “data-ink ratio” issued for the print media: The greatest amount of information, in an overview, with the least amount of ink, and on the smallest possible area. Edward Tufte quotes Richard Saul Wurman about the common misunderstanding about the economics of graphic design: “Everyone spoke of an information overload, but what there was in fact was a non-information overload.”14 Today, we produce and consume the daily news, technical instructions, and big chunks of our education and entertainment in successive forms like moving pictures. The exposure to cinema and TV has rendered the human IQ – at least the portions engaged in pattern recognition – culture dependent. The IQ, therefore, constitutes itself not as a natural given but dependent on the environment and culture – the so called “Flynn effect.” W. J. T. Mitchell congruously coined the term “pictorial turn” – images have taken over as the leading media to convey information – “Video killed the radio star.”15 Internet-based news threatens the classical newspaper. Nevertheless, moving images do not appear to be the all-purpose weapon we take them for today, for a number of reasons. Exhibit (a) regards our anthropological concerns as mentioned above. Exhibit (b) is the question of whether moving pictures render us couch potatoes, passive observers, and obese victims to what the menus offer best. Exhibit (c) is a warning about exclusive reliance on high-fidelity VR advice. We forget how to navigate; we only follow pre-programmed routes. What if the system breaks down? Are we in danger of becoming spatially illiterate? Exhibit (d) concerns the salesmanship aspect of moving picture formats. Various industries try to hook us up to their respective services. The longer we are plugged in, the more profitable for them. Why would we want to stay on for the duration of a movie if the information it contains often can be conveyed at a glimpse? What happened to Wurman RS (1976) What-If, Could-Be. An Historic Fable of the Future. Booklet, The American Institute of Architects National AIA Convention, Philadelphia 1976. Quoted after Tufte (2001), p. 90 15 The Buggles (1979) Video Killed the Radio Star. Song, Island Records 14

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the old-fashioned simultaneity of information-rich images? A classic map was the product of an exhausting generation of data in the field and painful elimination of characteristics that were not relevant to the map’s purposes. Although moving pictures are also based on a script, they do not necessarily have to employ the rigidity of classic map projections and generalizations. Traditional maps and globes were tough compromises between the precious data gathered in the field and the general map design. Now, with the abundance of data and established projection procedures, the thematic map design becomes the primary focus. We have to tell a story. As Karl Popper famously remarked about history, there is “no history without a point of view [...], history must be selective unless it is to be choked by a flood of poor and unrelated material [...] The only way out of this difficulty is, I believe, consciously to introduce a preconceived selective point of view into one's history; that is, to write that history which interests us.”16 We write the very history that is of interest to us. It is the thematic agenda of a map, its intent that renders the truth, the accuracy of data, an almost “forensic” aspect. I suggest a few known, if sometimes forgotten, editing strategies in order to distill stories out of the anti-Popperian flood of poor and unrelated data.

5 Fluent navigation between 2D and 3D Technology allows still images to be queued into sequences to form what came to be known as moving pictures. Let’s propose the opposite direction. Let’s freeze the movie, let’s unwrap the image, and let’s see what’s behind it and if it has anything else to say. Even more so since the ancient rift between painting and sculpture, between 2d and 3d, extends well into our contemporary software families. Prospective cartographic tools will have to provide fluent navigation between two- and three-dimensional data on top of their native software branches. I ask for universal algorithms to “undo” pictures, to strip images down to vector drawings, in order to understand what is behind their external appearance, and vice versa. It appears to be correct to design these image recognition algorithms as an inversion of the logics of CAAD & image production, in which a wire frame is usually mapped with surfaces in order to be rendered into a photorealistic image. Rather than putting vacation snapshots through image recognition software, it ought to be our aim to make a fundamental educa16

Popper (2002), p.139


tional contribution by offering professional visual expertise, a proficiency to investigate images, “analogously to skills in handling scripture” (Hans Ulrich Reck).17 As easy as it has become to render wire frames, it proves just as hard to recalculate a vector set out of an image with clear spatial indications like converging lines, overlaps and aerial perspective patterns. Large portions of cancer research are occupied with algorithms to sufficiently differentiate between regular-shaped organs and cancerous ones.

6 Comic culture: narration and speech bubbles The twentieth century separated scientific and artistic drawings. Modernism convinced the sciences to follow their compulsion to generate general knowledge, and the arts to indulge their urge for uniqueness. The genres developed separate codes of representation. Hybrid schemes were banned from the circus of publicity. Advertising, fashion, graphic design, and comics, most notably, only recently became re-accepted forms of high art. Comics suggest various means of reconciliation. Comics narrate stories and events in sequences of drawings. They also assign textual information to the images by surrounding texts with lines – the famous speech bubbles. We can learn either way – combining words and images has always been a challenge in cartography. Geographic information systems (GIS) have connected databases with graphic interfaces somehow. Lately, geodata interfaces have taken advantage of scaleless texts, i.e., texts are scaled according to amplification of the particular view at the screen. A lot of pathfinder applications already use speech bubbles and anchor lines, at least. Anyway, I am surprised about how often texts and graphics collide in maps – only to find ample relief in how superior comics take care of it. And, please, let’s stop overloading software, maps and models with noninformation. Let’s split maps up in sequences; let’s tell a convincing data story the way we got immersed in fairy tales when we were kids.

17

Reck, HU (2001) Zwischen Bild und Medium. Zur Ausbildung der Künstler in der Epoche der Techno-Ästhetik. In: Weibel P (Ed.): Vom Tafelbild zum globalen Datenraum. Neue Möglichkeiten der Bildproduktion und bildgebender Verfahren. Hatje Cantz, Ostfildern-Ruit 2001, pp.17-49, p. 25

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7 Isometric mapping Isometric, or congruence, mapping provides a bridge between maps and models. It can combine the clarity of a three-dimensional view and the accuracy of a plan – two of the proficiencies of cartography. The isometric, for a long time, had been confined to children’s books and assembly instructions. Today, it can be considered a key to explaining scaled spatial information. We ought to aim at a typical isometric viewing angle of around fortyfive degrees off the surface to reveal the maximum. Even modest topographies start to show up, houses do not block each other, and – often forgotten – shadows substantially add to the spatial information. I teach isometric drawing in architectural school, throughout the curriculum, and on various scales of application. Even freshmen are able to freehand sketch an 11 x 18-inch polychromatic isometric drawing of such architecturally complex buildings as the New Dresden Synagogue, the new Saxon Parliament and entire patches of the city of Dresden, up to a square mile, in less than two hours. We separate certain layers of information and encourage icons, symbols, and lettering on the side, thus allowing a piece of work that carries a ton of information with rather few lines, and putting a huge smile on the face of the author, who now has a strong sense of achievement. Tourism organizers have reluctantly started to beef up their map materials by adding the third dimension. A comeback of isometric projection in cartography is imminent.

8 High-density diagrams As with comics, high-density diagrams live in a niche. After tremendous success in facilitating sociological achievement in the 1930s, diagrams today are often reduced to meaningless pie charts full of visual junk. Starting with Charles Joseph Minard’s famous diagram about the “Losses of the French Army in the Russian Campaign 1812-13” (1869), Otto Neurath and others developed picture languages to illustrate the tremendous societal changes in the first half of the twentieth century, including such iconic maps as Harry Beck's “tube map” of the London subway (1931).18 After WWII, a breakthrough in the arts and graphic design as well as political liberalization allowed a strongly message-driven thematic cartog18

Hartmann F, Bauer EK (2002) Bildersprache. O. Neurath. Visualisierungen. WUV Universitätsverlag, Wien


raphy like Eduard Imhof’s “Thematische Kartografie” (1972), later opening up to turn-of-the-century projects like the Le Monde diplomatique “Atlas of Globalization” with Wladimir Tichunow’s anamorphous world map,19 and the University of Michigan’s “The PEW Global Attitudes Project” (2002) with the now-famous “Inglehart-Welzel Cultural Map of the World.”20 Such diagrams are profound tools for environmental, political and statistical purposes – even citizens with a less-than-keen interest in politics get something to help them decide whom they’ll vote for on Election Day.

9 Discreet future of “true 3d in cartography” Technological breakthrough is great in itself – as the entire history of western industrialization has made very clear. But with the world essentially mapped, the allure of how to represent geodata, the pragmatic aspect of information theory, enters the spotlight. With all due respect for scientific autonomy: What is it what we want to convey? What counts today is what novice users of cartographic products, be they digital natives or not, will get out of it. This customer orientation is a result of the ongoing erosion of the authority of experts, one that renders information more neutral, leaving interpretation to the user. It must have started a long time ago, at least with the Enlightenment calling for universal equality. It certainly was amplified by Friedrich Nietzsche’s modernist questioning of authority, the denial of humanity in Auschwitz, and subsequent high-tech catastrophes like Chernobyl, in which scientists, politicians and the media failed altogether. The erosion of authority certainly got streamlined by the digital revolution and the Internet, and has now produced a fundamental suspicion of almost everything, which could be to blame for increasing military secrecy and the tendency in private-sector research to patent results rather than publishing them. “True 3D” should not only describe the evolution of marketable 3d products and services but – more important – the support of the cognition that goes on in our heads, the learning curve. We arrive at Parmenides’ notion of reality again. While we do not have to declare the outside world of Tichunow W (2000) Anamorphotische Weltkarte. In: Le Monde diplomatique (2003) Atlas der Globalisierung Taz Verlag, Berlin, p. 47 20 Inglehart R, Welzel C (2005) Modernization, Cultural Change and Democracy. New York, Cambridge University Press, p. 64, based on the World Values Surveys under www.worldvaluessurvey.org 19

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appearances false, we very well can agree that the world is composed of ideas beyond the visible ones. Most people are extremely open to new products and fantastically tolerant of software bugs like clumsy menus. They nevertheless have developed a “push F1” expectation of a universal jinni to bottle- or spoon-feed them as appropriate. Here at least two productive positions emerge. One stipulates: Please, whenever possible, leave the ideas at the stage of concepts! Leave them alone. Accept that there are things that cannot be reduced to an outer appearance. Søren Kierkegaard’s famous word applies: “Schaffe Schweigen,” “Mandate silence!”21 The other one challenges scientific cartography to bend to the directive of “the customer is always right.” We seldom generate original data for a cartographic map or model any more. Today we network to compare, update and verify data. Not only has cartography changed from the small workshops to huge industries – primarily, the amazing push of neuroscientific insight, the challenging multilingualism of a global market, and substantial man-made changes to the world have rendered cartographic products equal to their respective services. Cartography has become a democratic endeavor. Open source and twoway applications are on the move. The future of “true 3d cartography” will be discreet, if not subliminal.

Literature Baudrillard (1996) The System of Objects (Système des objets [1968]). Verso, London, England New York, New York Friedberg A (2006) The Virtual Window. From Alberti to Microsoft. The MIT Press, Cambridge, Massachusetts London, England Kandel ER, Schwartz JH, Jessell TM, eds. (1981) Principles of Neural Science. Elsevier-North Holland, New York Lupton E, Miller A (1996) Design, Writing, research. Writing on Graphic Design. Phaidon, London Mitchell WJT (2005) What do Pictures want? The Lives and Loves of Images. University of Chicago Press, Chicago Popper, KR (2002) The Poverty of Historicism (1936). Routledge Classics, London England, New York New York Putnam H (1992) Representation and Reality. The MIT Press, Cambridge, Massachusetts London, England Sanders B (1998) The Private Death of Public Discourse. Beacon Press, Boston Soriano F (2002) Diagramas@... Decisión Gráfica, Madrid 21

Kierkegaard S (1958) Die Leidenschaft des Religiösen. Eine Auswahl aus Schriften und Tagebüchern (in German). Reclam, Stuttgart, p. 158

Truly modelling reality…? – Let’s improve our cognitive maps with a bastard mix of algorithms to “undo” pictures, isometric mapping, high-density diagrams and comic culture as integral sign posts for software development in cartography 95 Stafford BM (1999) Visual Analogy. Consciousness as the Art of Connecting. The MIT Press, Cambridge, Massachusetts London, England Tufte ER (2001) The Visual Display of Quantitative Information. Graphics Press, Cheshire Connecticut

Section 2: Planar Stereoscopic Hardcopies and Screens

Autostereoscopic Maps on the Basis of Lenticular Foils Gründemann, T. and Habermann, K.

True-3D Visualization of Glacier Retreat in the Dachstein Massif, Austria: Hard- and Softcopy Displays Bruhm, K., Buchroithner, M.F., Hetze, B. and Gindele, M.

Autostereoscopic Maps on the Basis of Lenticular Foils

Thomas Gründemann, Klaus Habermann mbmSystems GmbH, Dresden, Germany

Abstract The availability of high quality 3D-data sets, both geometry and texture, opens the door to produce high quality 3-dimensional displays. Most of the principles of 3D-displaying are based on viewing aids or special illumination and are therefore combined with tiredness by intensive using. One method is different in this case and additional the colour is also useful to transport content: Lenticular foil displays - consisting of small microlenses - offer the production of flat transportable displays which can be viewed in 3D without any viewing aids. These micro-lenses on a transparent plastic foil allow the map user to view the integral of two or more interlaced strips of stereo-mates through this foil with the left and right eye respectively. The calculation of both the strip width and the interlacing is done by means of commercially available software. The mbmSystems GmbH based in Dresden is the world-leading company in production of lenticular foil maps. The central parts of the map production are the modelling, rendering and interlacing of welldefined stereomates for the lenticluar foil displays. The print process runs in quality managed systems to assure the necessary accuracies. So a lot of possibilities for displaying are available, like changing letterings for different contents or multi-lingual maps, hovering lettering for the minimal covering of image content and flip images. Due to the interlacing of the sub-millimetre strips of the stereo-mates and the


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Thomas Gründemann, Klaus Habermann

resulting decomposition in x-direction the integration of well-designed and easily legible signatures and letterings represent a challenge. The presentation describes the lenticular lens principle, the image map generation and, in particular, the challenges of further research. Keywords: Autostereoscopic Maps, Lenticular,True-3D

1 Summary Reliefs or the third dimension are represented by using graphical elements (contour lines, shading) in conventional flat (two-dimensional) maps. The user of the map, however, may not comprehend the realistic relief forms. The need to give the user a real three-dimensional picture and, hence, an optimum spatial impression led to the use of stereoscopic methods. The character of a landscape can be conceived intuitively because the relief is not indicated abstractly but appears as stereogram. The 3D lenticular method is another possibility to visualise geodata in True-3D, besides stereoscopic imaging and similar methods (chromostereoscopy, holography). The method has enormous viewing comfort advantages since no viewing aid is needed.

2 Basics of the 3D lenticular method

Design and principle Printed lenticular maps (lenticular hardcopies) consist of 2 components to create the stereoscopic effect for the viewer without additional viewing aid (3D glasses or other devices for picture separation). These components are: x the lenticular foil and x the lenticular image.


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Fig. 1: Design and principle of the 3D lenticular method

The lenticular foil separates the perspective images allocated for the left and the right eye (partial image). For this purpose there is an array of parallel cylindrical lenses on the surface of the foil. The back side of the lenticular foil is flat and corresponds to the image plane of the lenticular image. The lenticular image consists of interlaced stripe-fragments of the partial images. The number of the partial images is not limited to 2 but can be up to 10 or more, thus giving the viewer a certain flexibility in the viewing angle without the need to fixate the viewing position.

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The separation of the images is subject to the optical properties of the lenticular foil. Parallel viewing axes are focussed to different stripes of the lenticular image. The left and the right eye of the viewer, thus, are shown only their respectively allocated image stripe. The viewer perceives a stereoscopic image due to the difference in perspective of the partial images.

3 Possible effects The great strength of 3D lenticular maps is not only the stereoscopic visualization of the relief as hardcopy but also their multitude of possible effects. 3.1 Floating labelling Geographical names, for instance, can be positioned floating above the relief. This layout gives a clearer impression of the map as the labelling appears detached from the relief and the connected map information. Smaller map overlap is another benefit. Due to the positioning above the relief and the use of several different partial images, the map user has the impression that it is possible to look at the map information “under” the label. 3.2 Alternating labelling The use of several partial images enables displaying different information within the 3D map image. This is reached by projecting the image information through the lenticular foil into the space within an angle of 50°. At a normal viewing distance this angle is big enough to see different information independently from each other without losing the stereoscopic impression. This property is perfectly useable to change, for instance, the language of a map. In this manner, the labelling within the map can change in multilingual regions without overloading the image with writing as the position of the text remains the same. Details and information content of the legend can also be changed with this effect, showing the desired information levels, respectively.


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3.3 Displaying of spatial and temporal changes Not only the text level can be changed depending on viewing angle but also the geometrical structure and texture of the map image. This enables direct comparisons of spatially changing structures or of changes over a period of time. The number of different scenarios depends on the possible viewing angle of the cylindrical lenses. In most cases it is limited to 2 scenarios because both eyes of the viewer must see the same scenario from any defined viewing position in order to get an optimum spatial impression. If more than 2 animation scenarios are required, a 3D impression cannot be realised. A horizontal orientation of the cylindrical lenses causes both eyes to receive the same image information. Tilting of the lenticular hardcopy changes the image content, making the visualization of more than 10 different scenarios possible, depending on the viewing angle of the cylindrical lens.

4 Production of lenticular hardcopies In recent years the availability of digital data, efficient modelling and visualization software and powerful computer hardware have been very good prerequisites to process topographic and thematic geo-information into True-3D cartographic images. The following steps are required to produce 3D lenticular hardcopies. First, the raw data must be read into and processed by 3D modelling and visualization software. Additional text can be positioned as well. Two virtual cameras are positioned to generate the model. The objective of taking these pictures is to capture image information of the object from different viewing angles. This results in two partial images out of different perspectives. When combining the 3D effect with other effects only a part of the virtual cameras captures the same scene. The other part captures the object with its changes. The use of digital data and processing also opens up possibilities to visualise the complete range of physical and virtual objects or of real or imaginary processes and conditions. For the output as analogue lenticular hardcopy, the separate partial images must be transformed into an edited printing file and subsequently printed. The edited printing file contains the interlaced partial images (lenticular image). The lenticular image can either be printed directly on the back side of the lenticular foil or onto another printing substrate with subsequent lamination on the lenticular foil. The direct offset printing

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method offers a very high fitting accuracy of the image stripes with the lenses. It is particularly suitable for a high number of copies. However, the calibration of the printing press and the production of the printing plate are very time-consuming. The fact that offset printing presses can only process foils with a thickness of up to 1 mm must also be taken into account. Therefore, only lenticular foils with a lens density of more than 50 lenses/inch can be used for the offset printing method. If lenticular foils of lower lens density (< 50 lenses/inch) are used, the image is printed on a printing substrate. Afterwards the lenticular foil is mounted to the printed image, either by adhesion (printing substrate sticks to the lenticular foil) or by glueing (printing substrate is connected to the lenticular foil with glue). This method is particularly suitable for a smaller number of copies. Direct printing on the back side of the lenticular foil reduces material and working expenditure, as no additional printing substrate (e.g. paper), to be stuck to the lenticular foil, is needed. Direct printing is also advantageous for outdoor use. As opposed to hardcopies that have the printing substrate attached to the lenticular foils with glue, there are no distortions in changing temperatures. Directly printed lenticular hardcopies, however, should have a scratch resistant lamination or protective lacquer on the back side preventing the separation of the paint from the lenticular foil during transport or use.

5 Further development At the moment high quality lenticular hardcopies can only be produced with offset printing. This method, however, can only be used economically for a high number of copies. Moreover, only foil formats with a maximum size of 100 cm x 70 cm and lens densities above 50 lenses/inch are possible for offset printing. In order to be able to produce also smaller numbers of copies in larger formats and with lower lens density, digital printing for lenticular hardcopies is being developed, which enables printing the image directly on the back side of the lenticular foil. The essential advantage of digital printing is the lack of additional printing substrate and glue, which are normally required to manufacture large-format lenticular hardcopies. Furthermore, a higher printing accuracy can be reached with direct printing. Such large-format lenticular hardcopies would make excellent panoramic displays, also for outdoor use. The suitability for such purposes,


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particularly under the influence of different climatic conditions, is yet another challenge for the production.

6 Conclusion The present article gives an overview of the application possibilities of three-dimensional and multitemporal visualizations of spatial data using the lenticular method. The big advantage of the lenticular technology lies in the perception of various information and content out of one image. Furthermore, neither an additional viewing aid, e.g. glasses for image separation (anaglyph technique, stereoscopic method) nor special lighting (holography) are needed. Particularly in the case of True-3D lenticular hardcopies, height relations can be directly conceived and interpreted from the stereoscopic image. But also for 2D effects, the lenticular technology offers a simple way to compare temporally or spatially changing objects or processes. Lenticular hardcopies will, thus, mainly be found in the realms of education or science or in representative applications. The results so far have shown that the lenticular technology has an enormous potential for future cartographic applications.

7 References Bahr, A., 1991: Stereoskopie - Räume - Bilder – Bildräume. – Thales Themenheft Nr. 49, 47 S., Thales Verlag, Essen. Buchroithner, M. F., Gründemann, T., Habermann, K., 2004: Theoretical Modelling Aspects of Bitemporal True-3D Hardcopy Production. – Gedenkband zum 60. Geburtstag von Prof. Dr. Armin Grün, ETH Zürich, Institut für Geodäsie und Photogrammetrie: 33-38. Buchroithner, M . F., Gründemann, T., Habermann, K., NEUKUM G. and the HRSC Co-Investigator Team, (2005/1): Multitemporale und großformatige Echt-3D-Hartkopien der Marsoberfläche. - Photogrammetrie – Fernerkundung – Geoinformation, Jg. 2005, Heft 5, S. 429-434. Buchroithner, M. F., Gründemann, T., Kirk, R. L., Habermann, K., (2005/2): Three in one: Multiscale Hardcopy Depiction of the Mars Surface in True-3D. - Photogrammetric Engineering & Remote Sensing, Volume 71, Number 10, S. 1105-1108. Buchroithner, M. F., Habermann, K., Gründemann, T., (2005/3): Modeling of Three-Dimensional Geodata Sets for True-3D Lenticular Foil Displays. Photogrammetrie – Fernerkundung – Geoinformation, Jg. 2005, Heft 1, S. 4756.

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Dickmann, F., Dodt, J., Schmitd, B., (2009): Zum Potenzial der Lentikulartechnik in der thematischen Kartographie. – Kartographische Nachrichten, Jg. 2009, Heft 6, S. 295-302. Gründemann, T., 2004/1: Grundlagenuntersuchungen zur kartographischen Echt3DVisualisierung mittels des 3D-Lentikularverfahrens. – 45 S., Studienarbeit, TU Dresden. Gründemann, T., 2004/2: Herstellung einer Echt-3D-Hochgebirgskarte auf der Basis des Lentikularverfahrens. – 88 S., Diplomarbeit, TU Dresden. Micro Lens Technology Inc, 2004: Choosing the Right Lenticular Lens. – http://www.microlens.com. Okoshi, T., 1976: Three-Dimensional Imaging Techniques. – 403 S, New York Academic Press.

True-3D Visualization of Glacier Retreat in the Dachstein Massif, Austria: Hard- and Softcopy Displays

Katharina Bruhm1, Manfred F. Buchroithner1, Bernd Hetze², Matthias Gindele3 1

Institute for Cartography, Dresden University of Technology, Dresden, Germany ²Center of Information Services and High Performance Computing, Dresden University of Technology, Dresden, Germany 3 ACADIS GmbH, Wiesbaden, Germany

Abstract Glacier recession is a global phenomenon subject to climate change. This also applies to the Dachstein Massif in die Eastern Alps of Austria. Based on historical and recent maps, and moraine mapping the glacier states from the years 1850, 1915 and 2002 were used as input for for photorealistic reconstructions and visualizations of the respective glacier states. A detailed digital terrain model and aerial photographs (2003 – 2006) were provided by the Government of Styria and Joanneum Research Graz. By means of the software packages ERDAS Imagine 9.1, ESRI ArcGIS 9.2, 3D Nature Visual Nature Studio 3 (VNS), Digi-Art 3DZ Extreme and Avaron Tucan 7.2 the glacier conditions during the “Little Ice Age” (+/- 1850) and the following two dates were reconstructed. Subsequently, several derivates of these data sets were generated. First, three individual overflight simulations were computed, permitting to obtain a realistic impression of the Dachstein Massif and its glaciers in 1850, 1915 and 2002. As a second embodiment product, a fast-motion dynamic visualization of the glacier recession was generated which M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_7, © Springer-Verlag Berlin Heidelberg 2012

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106 Katharina Bruhm, Manfred F. Buchroithner, Bernd Hetze, Matthias Gindele

illustrates their decrease in thickness. Third, combining both the flip effect and the true-3D effect achievable by lenticular foils, were applied to produce a multitemporal autostereoscopic hardcopy display. Fourth, the overflight simulation data sets were used to generate stereo-films which could then be displayed on back-projection facilities using either passive polarization glasses or active shutter glasses. Keywords: True-3D visualization, lenticular display, Cross-Media

landscape

visualization

glacier,

1 Introduction Glacier recession is a global phenomenon subject to climate change. This also applies to the Dachstein Massif in die Eastern Alps of Austria. Based on historical and recent maps, and moraine mapping the glacier states from the years 1850, 1915 and 2002 were used as input for photorealistic reconstructions and visualizations of the respective glacier states. The project described here is meant to show hauntingly the changes of the glacier coverage over the last 150 years. Only one data set was created for generating several visualizations, so-called Cross-Media products.

2 The Region The Dachstein Massif is situated in the Federal States Styria, Salzburg and Upper Austria and covers an area of nearly 900 square kilometers (cf. Figure 1). The High Dachstein is with 2.995 meters the highest point in this region. There are nine glaciers. Being part of the UNESCO World Nature and Culture Heritage Hallstatt – Dachstein / Salzkammergut and also as an important factor for the economy the retreat of the glaciers is monitored with concern.

True-3D Visualization of Glacier Retreat in the Dachstein Massif, Austria: Hardand Softcopy Displays 107

Fig. 1. Map of Austria in 1:2.800.000 showing location of the Dachstein Massif

3 Glacial Changes The glacial conditions in the Dachstein Massif at the end of the “Little Ice Age” around 1850 are only recorded in drawings and panoramic depictions by the Austrian geoscientist Prof. Friedrich Simony who explored this area between 1840 and approx. 1890. An analysis of moraines carried out by Michael Krobath and Gerhard Lieb from the University of Graz, Austria (Krobath & Lieb, 2001) was used for the mapping of all major Dachstein glaciers around the year 1850. At the beginning of the 20th century the Austrian and German Alpine Club (Alpenverein) began to explore the Dachstein Massif. Their “Alpenverein Map” published in 1915 contains a highly detailed depiction of the glaciological conditions. It reveals an explicit glacier retreat of approx. 30 % of the glacier area within the past 65 years (cf. Table 1). The glacier tongues receded above 2000 meter asl, implying a reduction of over 25 percent of their length. The most significant change was the separation of the Little Gosau Glacier from the Northern Torstein Glacier. Over 50 percent of their area were lost (cf. Figure 2).


Fig. 2. Orthophoto mosaic of the Dachstein Massif showing selected glacier states. Red: 1850, blue: 1915, green: 2002. 1: Southern Torstein Glacier, 2: Northern Torstein Glacier, 3: Little Gosau Glacier, 4: Schneeloch Glacier

Since 1946 the Alpine Club undertook continuous annual measurements of the glacier tongues and frequent surveys of their surfaces. The last accurate map was published in 2005 displaying the glacier state of 2002. Since 1850 the appearance of the area has been changing significantly: About 50 % of the glacier surfaces got lost. The snouts of the glaciers are now ending at an altitude higher than 2150 meter, and the recession process is still going on (cf. Table 1, Krobath & Lieb, 2001).

Table 1. Glacier surfaces of 1850, 1915 and 2002 in square meters. Glaciers Hallstatt / Schladming Glacier Great Gosau Glacier Little Gosau Glacier Northern Torstein Glacier Southern Torstein Glacier Schneeloch Glacier

1850 7568460 2559852 472440 101605 678195

1915 6114510 2007971 160530 88288 82581 458242

2002 3983797 1312897 95882 25750 4668 169478

True-3D Visualization of Glacier Retreat in the Dachstein Massif, Austria: Hardand Softcopy Displays 109 Total [sqm] Area loss since 1850 [%]

11.380.552

8.912.122 23,8

5.592.472 49,3

4 Data & Software

4.1 Data The used data sources were the moraine mapping published by Krobath and Lieb (2001), the 1:25.000 Alpenverein Maps from 1915 and 2005, a 10 m digital terrain model (DTM) provided by Joanneum Research Graz, Austria and aerial images (2003-2006) from GIS Styria. 4.2 Software By means of the software packages ERDAS Imagine 9.1, ESRI ArcGIS 9.2, 3D Nature Visual Nature Studio 3 (VNS), Digi-Art 3DZ Extreme V7, Awaron Tucan 7.2 the glacier conditions during the “Little Ice Age” (+/1850) and the other two dates were reconstructed.

5 Glacier Surfaces Based on the Alpine Club Maps of 1915 and 2002 and the publication of Krobath & Lieb (2001) displaying the glacier state of 1850 the necessary vector information was manually digitised. Afterwards 3D models of all glaciers were generated. However, there existed a problem of modeling the glaciers in the 3D software Visual Nature Studio. To solve this problem the differences between the glacier models of 1915 and 2002, and the 2004 DTM were computed. The results were grey-value images representing glacier heights. The elevation differences were separated in positive and negative areas (cf. Figure 3). Accurate information of the elevation of the glaciers in 1850 was not available. So, the glacier surfaces were inferred from a publication of Brückl et al. (1971).


Fig. 3 Grey-value images of the Great Gosau Glacier 2002 separated in positive (right) and negative (left) areas

6 Cross-Media Products The generated products are: x Overflights x Film animation of ice thicknesses x Auto-stereoscopic lenticular foil display x Stereo-overflights for back-projection facilities. 6.1 Overflights with Visual Nature Studio (VNS) The overflights give an impression of the last glacier maximum around 1850 and the subsequent retreat. VNS is a 3D visualization software package which is specialised for GIS software users. This software package offers the opportunity to import various GIS or geospatial data like vector shape files in the selected geometric reference system.


The materialization is quite easy. The DTM was imported as ASCII file and the vector polygons as shape files, the aerial photographs were used as texture. The grey-value images of the glacier surfaces were utilised to adapt the digital terrain model within the vector polygons. With only few processing steps three rather photorealistic models of the Dachstein glaciers of different points in time were created (cf. Figure 4).

Fig. 4 Dachstein Glacier in 1850

A close look at the glaciers, however, reveals that the typical marginal bulges of the glaciers are missing. In VNS glacier margins cannot be represented in their typical photorealistic way. This would imply the use of extra software. In order to further model the 3D models an export into a more general 3D data format like PRJ is needed. These models can then be displayed using 3D Studio or similar programmes, however, a decrease in visual quality and accuracy has to be accepted. This can be explained the limited possibilities provided by the export settings of VNS. Due to time reasons the glacier margins have thus not been altered. 6.2 Film animation of ice thicknesses As a second embodiment product, a fast-motion dynamic visualization of the glacier recession was generated which – due to some slight vertical exaggeration – also effectively illustrates their decrease in thickness, the so-called downwasting. In 1968 the Federal Office of Meteorology and


Geodynamics in Vienna performed seismic measurements at the Dachstein glaciers in order to determine the average ice thicknesses (Brückl et al., 1971). These measurements, repeated in 2000 with the help of GPS, form the basis for the representation of the inferred thickness around the year 1850. For the glacier states 1915 and 2002 the grey-value images of the glacier surfaces contain the ice thickness (see above). The aforementioned animation, realised by means of Tucan, shows a significant reduction in glacier thickness over the last 150 years. The Tucan software was used for the representation of the 3D model computed in real time. By means of this software the “unintelligent” geometric input data were converted into complex scenes originates (cf. Figure 5). Both free navigation in a scene and the movement along a pre-defined path are possible. Besides a free viewer, for the displaying of virtual scenes also a professional variant is available. Active and passive stereovision are supported. The software was designed in such a way that it is simply applicable by users without Virtual Reality expertise and programming knowledge. Tucan offers many functions for the production even of complicated animations. Based on an integrated Interface Designer it is possible to steer moving geometries as well as dynamic and particular system settings e.g. by buttons (www.awaron.com/en/products/tucan). This functionality was used for the representation of the glacier changes.


Fig. 5. Screenshot showing the Tucan software work environment

6.3 Auto-stereoscopic lenticular foil display This display (cf. Figure 6) is a multitemporal auto-stereoscopic hardcopy display viewable with unaided eyes. Two effects, the flip and the true-3D effect were combined. The basic principle of the lenticular method is the artificial stereoscopic viewing created with the help of semi-cylindrical parallel micro lenses running on the top side of a transparent synthetic foil. Under these lenses interlaced images are arranged which means under every lens lies one pixel column of all used stereo-mates (cf. Figure 6). For stereoscopic viewing the left and the right eye need images projected in different directions. The foil permits the separation of these stereo-mates. Incoming optical rays are focused by the lenticular foil at several strips of the image. By turning or tilting the lenticular display the observer changes his viewing angle and has the opportunity to view the spatially separated scene data. More information of this topic is given in a monograph by Thomas Gründemann (2004) and other papers published by the 3D visualization


group of the Institute for Cartography at the Dresden University of Technology (e.g. Buchroithner et al. 2005a, 2005b).

Fig. 6. Principle of lenticular foil method showing the interlacing of stereo images

The stereo-images were generated using the 3D modeling software Visual Nature Studio by simulating an overhead stereo-camera with parameters especially calculated for this project. For the lenticular display two images of every glacier date were computed. After the rendering these


images are taken and served as input for further processing by the lenticular software 3DZ Extreme V7. 3DZ is an advanced and easy-to-use lenticular and barrier screen printing software (www.digi-art.de). It was used to interlace the images.

Fig. 7. Layout of the lenticular map

6.4 Stereo-overflights for back-projection facilities The overflight simulation data sets were used to generate stereo overflights by Tucan which were then displayed on back-projection facilities. These walkthroughs, rendered in real-time, are shown trough a translucent screen to the spectators who observe the displayed scenes from the other side of the screen. Using either passive polarization glasses for stationary backprojection facilities or active shutter glasses for portable ones, this technique is unfortunately not “auto”-stereoscopic. At the Dresden University of Technology both types of back-projection facilities are used for teaching purposes. This technology achieves a so far unequaled quality in stereovision. This is certainly subject to the high resolution of the used projectors which is currently in the range of 1400 x 1050 pixels for portable and 1920 x


1200 pixels for stationary high-end devices. For the control of the graphics periphery an NVIDIA Quadro graphic card is used. The Digital Terrain Model of the present test-site comprehends 1.600.000 polygons which, for the reason of real-time visualization, had to be converted into an elevation grid. Even the total number of polygons covering glaciated terrain amounts to more than one million.

7 Conclusions All the above mentioned products are based on the same data sets. In the sense of cross-media visualization they are planned to be presented to both the scientific and the public communities at various occasions. Initial internal tests with students already revealed the high potential of these individual products for a better understanding of the still ongoing glacier retreat in the Alps. To the authors’ knowledge all the above described stereo-visualization methods have never before been applied to real and simulated – in our case historical – geodata. This premiere is meant to demonstrate different approaches of stereo-visualization for environmental purposes. Furthermore, the applied display techniques are supposed to give an impression of the great variety of 3D viewing hard- and softcopy methods. Due to the different media forms used, identical data bases can be presented to different user groups. Overflight simulations and lenticular foil displays proved to be particularly well suited for tourism purposes. Animations might help to improve the understanding of complex geoprocesses. Despite their restricted possibilities for the presentation of dynamic processes, lenticular foil hardcopy displays have significant advantages for outdoor use. They require neither viewing means nor electric power. The applied softcopy technology needs, albeit, stereo-glasses but it allows the visualization of photorealistic scenes with a so far unequaled quality, also in animated form. This Paper is an up-dated and changed version of a paper given at the 4th. International Workshop of 3D GeoInfo in Gent, November 2009 and published in Developments in 3D Geo-Information Sciences (Lecture Notes in Geoinformation and Cartography), Ed.s: Tijs Neutens, Phillipe de Maeyer, Springer, Nov. 2009.


References Brückl E, Gangl G, Steinhauser P (1971) Die Ergebnisse der seismischen Gletschermessungen am Dachstein im Jahre 1968. Arbeiten aus Zentralanstalt für Meteorologie und Geodynamik, Vol. 9, Wien Buchroithner MF, Gründemann T, Randolph KL, Habermann K (2005a) Three in one: Multiscale Hardcopy Depiction of the Mars Surface in True-3D. Photogrammetric Engineering & Remote Sensing Okt. 2005 : 1105 - 1108 Buchroithner MF, Habermann K, Gründemann T (2005b) Modeling of ThreeDimensional Geodata Sets for True-3D Lenticular Foil Displays. Photogrammetrie – Fernerkundung – Geoinformation 2005/1 : 47 - 56 Gründemann T (2004) Grundlagenuntersuchungen zur kartographischen Echt3DVisualisierung mittels des Lentikularverfahrens. Pre-Thesis, Dresden University of Technology Habermann K (2004) Conception for True-3D Maps. Presentation at the XIII. Cartographic School 2004 of University Breslau: Co zwie się koncepcją mapy? - What is called the Map Conception?. pp. 76 – 88. Krobath M, Lieb G (2001) Die Dachsteingletscher im 20. Jahrhundert. K. Brunner (Editor), Das Karls-Eisfeld. Research Project at Hallstätter Glacier. Wissenschaftliche Alpenvereinshefte 38: 75 - 101 Mandl F (2006) Der Hallstätter Gletscher. Alte und neue Forschung. ALPEN – Festschrift: 25 Jahre ANISA : 202 - 215 Simony F(1885) Ueber die Schwankungen in der räumlichen Ausdehnung der Gletscher des Dachsteingebiges während der Periode 1840 – 1884. Mittheilungen der kais. königl. Geographischen Gesellschaft in Wien. Vol. 28 : 113 - 135 Simony F (1889). „Das Dachsteingebiet“. Hölzel, Wien-Olmütz 3D Nature (2009). www.3dnature.com Awaron Tucan (2009) www.awaron.com/en/products/tucan Digi-Art (2009) www.digi-art.de Planai (2009) www.dachstein.planai.at

Section 3: Physical Terrain Models

Creating Physical 3D Maps Using Rapid Prototyping Techniques Rase, W. -D.

Creating Physical 3D Maps Using Rapid Prototyping Techniques

Wolf-Dieter Rase Federal Office for Building and Regional Planning, Bonn, Germany

Abstract To build multicoloured physical models of three-dimensional cartographic objects computer-controlled devices can be used which were developed for the fast and inexpensive production of mechanical parts. Such objects can be a landscape with relief, a city model, or a continuous surface interpolated from statistical data. The main groups of rapid prototyping technology – aggregation, removal and, transformation – are presented, including the machinery to build physical models, and a new relative, laser subsurface engraving. Examples of surface models built by a 3D multicolour printer demonstrate the capabilities of the technology. A new WWWbased service is described which enables the production of 3D relief models covered by satellite imagery, topographic maps and user-supplied GPS tracks. Keywords: 3D maps, 3D printing, cartography, GIS, rapid prototyping, spatial monitoring

1 Virtual and physical reality The enhanced cost-effectiveness ratio of computers and graphic peripherals has provided advanced methods to generate photo-realistic scenes, which are known as virtual reality (VR). Developers and users of geographical information systems have adopted VR to visualize spatial obM. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_8, © Springer-Verlag Berlin Heidelberg 2012

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jects. Computer graphics and VR have also facilitated the transition from static planar maps on paper or fl at displays to perspective and stereographic representations, which can also include the time dimension. Such dynamic visualization has been made possible by high-performance desktop computers and high-capacity distribution media, such as the World Wide Web, the CD-ROM and DVD. Perspective drawings on 2D media take advantage of the viewer’s lifelong experience in recognizing and interpreting depth cues in pictures. The main shortcoming of using perspective drawings for cartographic applications is the inability to obtain distances and directions from measurements in the picture, although interactive software provides solutions to that problem. Stereoscopic displays make use of the ability of the human brain to construct a 3D mental model from two slightly different images, one corresponding to each eye. Stereo images may be provided by binocular viewers, shutter glasses, lenticular and barricade displays. Stereoscopic viewing can also be induced by non-binocular optical effects, such as SIRDS (single image random-dot stereograms) or chromostereoscopy (Rase 2003). Despite the availability of virtual reality technology, physical models of buildings are still requested in architectural competitions, even though VR techniques are able to provide more visual information than a model. For example VR allows interiors to be visualised from different viewpoints and under varying light conditions during a walk-through, or the view through a window, in both directions, can be generated. Why are those rather expensive architectural models still requested? One reason may be that the cost of the model is a marginal quantity compared to the cost of the competition, let alone the real building. Probably architects have also a fondness for the haptic experience, the opportunity to feel an object with their own hands. Physical models have the advantage over 2D drawings that slight movements of the head or body suffice to compare heights, to solve viewing ambiguities or to reveal parts of the model that might be obscured in a fixed view. In case of non-dynamic media multiple drawings it may be necessary to present all parts of a scene. The quest for haptic experience may be valid not only for architects but also for decision-makers in regional planning with a limited experience in map reading. It is suspected that under certain circumstances a real 3D model is able to transmit the cartographic message much better and faster than a two-dimensional map.


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2 Rapid prototyping Rapid prototyping (RP) is the automatic construction of physical objects using solid freeform fabrication within short timeframes. Numerically controlled machines capable of the production of mechanical parts have been in use for more than four decades. Advances in microelectronics have led to computer-controlled devices which are able to build physical models at reasonable cost. The prototypes serve mainly to judge on the form and appearance, in certain cases to evaluate the mechanical function (Grenda 2009). Usually the prototypes are not exposed to the mechanical stress that their real counterparts have to withstand, for example the prototype of a steering wheel for a car. Thus it is not necessary in most cases to use the same material of which the final part will be made. 2.1 Main groups of rapid prototyping techniques The different technical approaches for the computer-assisted production of parts can be subsumed under four headings with equivalents in the fine arts: x Removal: A block of material is cut with a tool that removes successively small quantities of material until the final form is reached, as a block of marble is transformed into a sculpture (the Michelangelo method). x Transform: The material is formed by pressure and heat, as a blacksmith forms a red-hot bar of iron (the Chillida method). x Aggregation: A part is built up from small amounts of material, in the same way a sculpture or a scale model is formed in plaster or some other plastic material (the Rodin method). x 3D drawing: tiny points inside a glass block are melted by a laser beam and become opaque (the Dürer method). An example of the Michelangelo method is numerically controlled milling. Rotating tools of different size and shape moving in three and more degrees of freedom carve material from a block of metal, wood or plastic until the final form is reached. NC milling is slow and expensive compared to the other techniques available today. Colouring must be added in a manual process, for example by airbrushing, or in a transitory mode by projecting an image onto the model with a beamer. An exception is the production of large relief models by the company STM (www.stmusa.com) using computer-controlled inkjet nozzles moving in three dimen-

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sions to apply texture on the surface. The machinery is unique, so the models have to be produced in Fillmore, CA, and shipped to the customer. The artist Eduardo Chillida created huge metal sculptures by industrial forging of iron rods and bars (one of his sculptures is placed in front of the Office of the Federal Chancellor in Berlin). The transformation by heat and pressure is also used to create multiple copies of 3D maps. In France bookstores offer terrain models of regions and départements, depicting height, rivers, streets and settlements. The 3D models, available at moderate prices, are made by thermoforming a colour-printed foil by applying heat, vacuum or pressure using a mould, which, in most cases, is produced by NC milling (www.georelief.fr). The aggregation of material, the Rodin method, has the greatest potential for rapid prototyping in general and for the creation of city and cartographic surface models in particular. The integration of colouring into the production process opened new horizons for cartographic applications of rapid prototyping (more in the following section). The 3D analogy to 2D drawings is laser subsurface engraving which, strictly speaking, does not belong to the rapid prototyping family, but uses the same data and files to encode the model, and computer control to move the laser beam along three axes. 2.2 Printing in three dimensions The most frequently used technologies for rapid proto typing belong to the Aggregation group. Stereolithography was the first technique for rapid prototyping. A computer-controlled laser beam induces a phase change in a thin layer of photosensitive liquid. The liquid changes phase – becomes solid by polymerization – where the laser beam hits the surface. A new layer is then built on top of the solidified layer, and the procedure is repeated until the object is finished. Other devices aggregate drops or streams of thermoplastic material to build the model. The material is heated in a multi-nozzle printhead. The liquid material is deposited on the previous layer. Outside the printhead the material cools down and solidifies again. There were also devices that use laser-cut paper sheets laminated to a block (LOM), but they have been superseded by less expensive techniques with more capabilities, such as the powder-based devices which are used now for most applications. A thin layer of a powder, such as starch, plaster, photopolymer or metal, is deposited onto a building platform. The regions of the layer that are to become part of the model are fixed by selective spraying of an adhesive, by polymerization with an UV light beam, or by local heating with a laser


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beam (selective laser sintering, SLS). When the first layer has been fixed the second layer is deposited, and so on, until the final layer is accomplished (fig. 1). After completion of the model the loose powder is removed by a sort of vacuum cleaner and an air jet. Most devices allow recycling of the unused material.

Fig 1. Building steps in a 3D printer (colour version on CD-ROM)

Which process or device should be used depends on the purpose for which the prototype is intended. For instance, stereolithography achieves very smooth surfaces, but is expensive. Selective laser sintering, also called direct metal printing, produces metal parts which are stronger than parts from other processes. The artist Bathsheba Grossman uses direct metal printing to create multiple copies of sculptures based on mathematical concepts (www.bathsheba.com). A combination of starch powder and wax can be used to build a pattern for investment casting. The part is covered with refractory slurry and then the wax is vaporised and replaced by

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the molten metal. Some powder materials can be finished with tools used for wood and electroplated subsequently to give the appearance of metal.

2.3 Multicolour 3D printers Colour is an essential graphic variable in cartography and model visualization. Until a few years ago the direct application of colour during the buildup stage was not available, and the raw models had to be coloured manually. The application of colour must be integrated into the building process of the model to keep the production within a reasonable cost frame. In recent years new RP devices were developed which can apply colour in high resolution and in many program-controlled shades, which makes it feasible to use the technology to build physical models of cartographic objects. The rich colour spectrum and the use of standard inkjet printer parts probably caused the manufacturers to call their devices 3D printers. The first 3D printer with integrated high resolution colour capability was introduced in 2001 by the company ZCorporation (www.zcorp.com). In addition to the transparent glue the device applied three coloured glues containing pigments of the subtractive base colours cyan, magenta, and yellow. The finished model is usually infiltrated with a hardening liquid, such as epoxy rosin or cyanoacrylate, which enhances the colour luminosity, improves the mechanical strength and protects against high humidity. The 3D printers of ZCorporation are still the only devices on the market (also sold under a different brand name) that provide multi-coloured parts. For the top member of the family, the 3D printer Z650, a black print head was added to solve the problem of the imperfect gray and black shades created by mixing cyan, magenta and yellow pigments. The Z650 provides real CMYK colours with a resolution of 600 x 540 dpi. The capability to provide colour integrated into the build process opens many new applications for RP aside from cartography and GIS. For instance multi-coloured models of molecules, buildings, city models or plants can be produced. There are many potential uses in medical visualization improving clinicians’ comprehension and understanding of data from x-ray or magnetic resonance scanners. The software for the 3D printers slices the numerical representation of the model into layers of user-selectable thickness, in the range 0.089 to 0.102 mm. The thickness of the layer determines the resolution in the zdirection, and hence the production time. A value of 0.1 mm was used for the surface models referenced here. From two to four layers can be built


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per minute. The Z650 printer can handle parts up to 254 x 382 x 200 mm, dependent on the model size and the number of base colours used.

Fig. 2. Physical model of an interpolated smooth surface representing the average prices in Euro/m² for building lots in Germany (colour version on CD-ROM)

2.4 Laser subsurface engraving Laser subsurface engraving (also known as laser etching) is performed by a computer-controlled device where a focused laser beam melts a tiny spot in a glass block, destroying locally the transparency of the glass. The molten spots blend into a 3D picture, which might represent a building, a human portrait, or a cartographic surface. The laser beam and its focus are

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moved in relation to the glass block using data derived from a numerical representation of the object. It is obvious that the melting process has to start with the lowest layer, otherwise the laser beam would be occluded. The equivalent 2D representation is a pen drawing or etching which is why I like to call this the Dürer method. The object inside the glass block is monochrome (fig. 4). Putting it on a pedestal providing adequate illumination is advisable to insure good visibility. Nearly identical VRML files as with the 3D printer were used to generate the surfaces inside the glass block. The files were sent by e-mail to the company which builds the computer controlled laser engraving devices (www.vitro.de). The manufacturer of the device offers now additional software to its customers, intended to improve the visual appearance of the models in the glass block. A franchise organization operates shops in several countries, providing etching devices and 3D cameras necessary to do 3D portraits on the spot (www.looxis.com). Some of these shops are able to accept 3D files and produce the laser etching for customers.

Fig. 3. Enlarged part of surface model in Fig. 2, legend and text (colour version on CD-ROM)


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Fig. 4. Glass block with laser-etched 3D surface. Same content as in Fig. 2 (colour version on CD-ROM)

3 Examples of cartographic 3D models For the visualization of cartographic surfaces generated from demographic, socio-economic or accessibility data a number of physical models were produced. Only three typical examples can be presented here. At first a few details on the numerical definition of the models and the production workflow are given.

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3.1 Model representation and workflow The continuous surfaces depicted in the models were interpolated from point or polygon data, with the geometric base data prepared using a standard GIS package (ESRI ArcGIS). The interpolation of the surfaces and the creation of the numerical representation of the 3D models were done using our own software. The skin of the model – surface, base, legends, text strings – is represented by an irregular triangular mesh which can be stored in different file formats used for 3D models. In our case the VRLM97 or PLY file format were used. Many CAD programs and viewers are able to display VRML files for visual inspection of the models, including syntax checks of the triangular mesh. It is possible to cover the surface with a texture defined in a geo-tagged raster file to depict lines, text strings and other relevant geometric information. The distortion of the pixels on steep slopes of the surface, however, results in a fuzzy appearance not acceptable for maps. Thus the boundaries and other lines are represented by thin tubes composed of small triangles. The skin of the legends and 3D text strings are also represented by triangular meshes. The 3D text is generated by extruding the glyphs (polygons) defining the characters in the TrueType font files. The graphic resolution of the glyph is user-selectable, and depends on the actual character size. Any TrueType font can be used, provided that the syntax of the glyphs is correct. The same approach is used to construct 3D point symbols from symbol definitions in TrueType fonts, such as the tiny planes representing airports in fig. 6. The interpolation and the triangle generation including the meshes representing the tubes, areas, legends and 3D text, are done with our own software. Standard viewers for 3D models are used for simple visual checks of the models. Before the files are transmitted to the 3D printer a thorough check is performed to reveal and correct serious problems which could spoil the actual build process on the 3D printer. Even though 3D printers now cost less than half as much as a high quality mechanical 2D plotter did about 20 years ago, it is not economical to buy a 3D printer for only occasional use. So the services of a contractor were used to build the models (www.4dconcepts.de). The VRML files with the model representations were sent to 4Dconcepts as attachments to e-mails. Assuming that no errors are detected during an extra check at the contractor’s premises, the model is built on the printer, infiltrated with the stabilizing liquid, and then returned to the customer by a parcel service.


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3.2 Surface of average prices for building lots The heights of the surface in fig. 2 represent the average prices for building lots, estimated from actual sales in previous years. Interpolation of the polygon-based data (counties in Germany) was performed using the pycnophylactic interpolation method (Tobler 1979; Rase 2009). Figure 3 is a closeup of the same model, showing lines, legend and text strings.

Fig. 5. Bivariate trend surface (order 5) and colour-coded cylinders representing the values of the residuals. Cyan: residuals are negative (actual values less than the surface values); magenta: residual values are higher than the trend surface. Content of model: see text. (colour version on CD-ROM)

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3.3 Trend surface analysis of unemployment Figure 5 is a photograph of a model representing a trend surface interpolated from unemployment data. A bivariate least-squares polynomial of order 5 describes the overall spatial trend of unemployment, with high values in East Germany and low values in Southern part of Germany, as expected. The representation of the surface is supplemented by columns representing the residual values, the deviation of the actual value at each point from the value of the trend surface. Because the negative value (unemployment less than the trend) cannot be visualised by holes colour codes are be used to express negative (cyan) or positive residuals (magenta). In Berlin and the region southeast of Berlin, for example, the actual values are lower than the trend, with columns coloured cyan. 3.4 Travel distance to airports The model in figure 6 represents a variable resulting from accessibility computations for the railway and road network in Germany. The heights of the surface are proportional to the average time distance in minutes using a car to the next airport in Germany and outside Germany in the vicinity of the border. The surface was interpolated to a regular grid from the time distance values at the access points (ca. 20,000) in the network, using the Modified Shepard interpolation method (Renka 1988). At the points near to the airports the surface is almost zero (minimum travel distance). The highest values occur at the peripheral regions.


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Fig. 6. Surface of time distance to the next airport (accessibility). The surface heights are proportional to the travel time by car to the next airport in Germany and the airports in the vicinity of the outer boundary. (colour version on CDROM)

4 Relief models with user-selected texture The most recent addition to the facilities for creating “true” 3D models is the WWW-based service offered by LandPrint (www.landprint.com). After downloading a Java applet the user can select any place on earth by typing a name. The application zooms in to that place, provided the name is stored in the data bank. The user can define a window and select a multiplication factor for the height from 1 to 5. The textures overlaid on the relief include satellite images and topographic maps at different scales, at the

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moment US maps only. The relief data and the satellite imagery are provided by Google Earth. The use of Virtual Earth data is planned.

Fig. 7. Screenshot of the user interface to create a the relief model. Location: Chaîne des Alpilles and city of Saint Rémy-de-Pro vence, France. Red line: window; blue line: GPS track recorded during a bicycle tour. Small window at the lower right: 3D model preview. (colour version on CD-ROM)

Relief models intended for regional, environment or traffic planning, recreation development or disaster prevention and analysis can be covered not only with satellite imagery, but also with topographic maps. At the moment only topographic maps of the USA are available. The application of user supplied geo-tagged imagery is in preparation. The customer can upload his own GPS tracks to be displayed on the relief model as lines in a user-selectable colour. The tracks are usually collected automatically by a GPS recorder during a roaming, canoeing, biking or geocaching tour. The addition of GPS tracks enable outdoor-oriented customers to build their individualised relief models, including their own routes, e. g. as a reminiscence of an outstanding tour in a beautiful environment, or to impress their friends by exaggerating the height factor. The relief models can be built in different sizes up to 25 x 25 cm. The company ships the models to the customers by a parcel service, but only within continental USA. The prices for the models are very competitive. For European customers interested in building personalised relief models two European companies so far have licensed the software from LandPrint


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(as of November, 2009). A Danish firm (www.3dlandprint.dk) offers the service with its website in Danish, but is considering to add web pages in English. The other licensee is located in Great Britain (terrainprint.co.uk). Both firms ship the models to customers in Europe, and are preparing to provide European topographic maps.

5 Summary Physical models of GIS objects are unlikely to replace paper maps or virtual reality techniques. However, a model has all the advantages of a perspective drawing or a stereogram. In addition, viewing ambiguities, such as the inversion of the depth impression, a recurrent problem with 2D drawings and sometimes also with stereograms, can be resolved by a minor movement of the head or body. The estimation of distance and height within the model is easier with a physical model due to the lifelong experience with 3D views. When a group of people are trying to grasp a spatial situation or process a physical model can have advantages over VR methods. VR equipment is still expensive, less transportable than a physical model, and is not usually able to support multiple users. The production of a physical model, to be fair, is not cheap either, although the prices became more affordable recently. A physical model can be used for representative and promotional purposes, for example on display in the entrance hall or an office, or exhibited at a fair. In this context models have an important job as conversation pieces. The technical explanation how the model was built can lead to a discussion of the problem that the model is trying to clarify. This is very important for environments where decision makers have no immediate relationship with spatial science, GIS or cartography. The model is the medium to introduce the message in a roundabout way, a kind of subversive cartography. An illuminated glass block with the etched object inside falls into the same category, as an eye-catcher or conversation piece. It can also serve as a rather inexpensive theme-related trophy or a personalised present. Something unexpected happened when I showed these models to visitors or colleagues for the first time: nearly everyone spontaneously tried to touch the surface of the model. To touch the material and the surface forms, to use the haptic sense, is obviously a basic desire, equivalent to the desire to use the other senses. Touching is not reserved for people with a visual handicap, although they would certainly benefit from the economic advantage of producing special maps by rapid prototyping techniques (see also Koch 2009, Schwarzbach et al. 2009).

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References Grenda, E (2009): Printing the future. The 3D printing and rapid prototyping sourcebook, 3rd edition. Castle Island Co., Arlington, MA http://home.att.net/~castleisland/ Koch, WG (2009) State of the art of tactile maps for visually impaired persons. ICA SPIE Europe Symposium True-3D in Cartography, 24–28 August 2009, Dresden Rase, WD (2003) Von 2D nach 3D – Perspektivische Darstellungen, Stereogramme, reale Modelle. In: DGfK (ed.), Visualisierung und Erschließung von Geodaten, Kartographische Schriften, Bd. 7, Kirschbaum-Verlag, Bonn, 2003, 13–24 http://www.wdrase.de/Von2Dnach3D.pdf Rase, WD (2009) Visualization of polygon-based data as a continuous surface. Manuscript 2009 http://www.wdrase.de/VisualPycnoInterEngl.pdf Technical report (in German) http://www.wdrase.de/PycnoInterReport.pdf Renka, RJ (1988) Algorithm 660: QSHEP2D, Quadratic Shepard method for bivariate interpolation of scattered data. ACM Transactions on Mathematical Software, Vol. 14, No. 2, June 1988, 149–150 Schwarzbach F et al. (2009) Physical 3D models from LIDAR data as tactile maps for visually impaired persons. ICA SPIE Europe Symposium True-3D in Cartography, 24–28 August 2009, Dresden Tobler, WR (1979) Smooth pycnophylactic interpolation for geographical regions. In: Journal of the American Statistical Association, 74, 357 (1979), 519–535 http://www.geog.ucsb.edu/~tobler/publications/pdf_docs/geog_analysis/Pycn o.pdf

Section 4: Tactile Maps

State of the Art of Tactile Maps for Visually Impaired People Koch, W. G.

Hypsometry in Tactile Maps Voženílek, V., Růžičková, V., Finková, D., Ludíková, L., Němcová, Z., Doležal, J., Vondráková, A., Kozáková, M. and Regec, V.

Physical 3D models from LIDAR data as tactile maps for visually impaired persons Schwarzbach, F., Sarjakoski, T., Oksanen, J., Sarjakoski, L. T. and Weckman, S.

State of the Art of Tactile Maps for Visually Impaired People

Wolf Günther Koch Institute for Cartography, Dresden University of Technology, Dresden, Germany

Abstract Beside cartographers computer scientists, blind persons pedagogues, and psychologists work worldwide in the field of tactile cartographic media. In the last decades this interdisciplinary research led to significant results. Within the last years new methods, technologies, and devices have been developed. Nevertheless traditional (classical) and new tactile media exist side by side. New media are characterized by the application of computers, GIS, multimediality, internet integration, real and virtual displays. In the widest sense also navigation systems with and without GPS application can be included. The current level of development should be characterized according to the following aspects: mediaforms, symbols and map design, production methods. Today the classical hand maps (single maps), atlases (map series) and globes are still produced. Tactile wall maps are rare. With the new tactile cartographic media the audio-tactile dialogue systems have fully matured and are used practically. Virtual displays and virtual maps are further perfected. A comprehensive standardization of the tactile symbols and the use of symbols has not been reached. A system of general design rules was accepted. Extensive theoretical investigations have led to partly new knowledge. Vasconcellos (1996) adapted the system of visual variable (J. M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_9, © Springer-Verlag Berlin Heidelberg 2012

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Bertin) for the field of tactile maps. Geiger (2001, 2008) studied the possibilities and limits of the use of cartographic representation methods for thematic tactile maps. First connections und dependencies on structure and function were extensively examinated by Geiger (2008). Presently in principle all maps for blind and visually impaired people can be automatically or partially automatically produced. Therefore the following technologies are used (with different frequency): Thermoform (vacuum forming), Microcapsul (-paper) and Fuser, Embossing, Tactile Print, other. Today with the help of novel technologies the internet can also be used. Particularly since 2007 many new results were published. Also the practical use of these technologies is in its initial state. The number of the new systems is very big. The chairman of the ICA Commission on Maps and Graphics for Blind and Partially Sighted People, Dan Jacobson, sees (2007) the future of tactile cartography in the use of multimodal dynamic computer interfaces. Keywords: Tactile Map, tactile display, tactile printer, map design, research methods, tactile production methods

1 Background Tactile Mapping is a sub-domain of the much broader studies on accessing image-based information through touching. As a sub-division of cartography it looks for optimal ways of representing spatial information for people who are blind and/or partially sighted. Today the tactile cartographic communication relies more and more on multimedia. Neverless, the haptic perception by this transfer of information takes an important part. The active touching hand of the map user notices raised point, line, and area symbols. It acquires information from the place, distance, and shape of these figures and structures. This is a sequential process, in which the fingers follow raised symbols and gradually build up an overview of spatial relationships (Tatham 1991, Perkins and Gardiner 2003). Because the colour is not available as a carrier of information as a rule, an essential meaning relates to the relief resp. relief structures on the tactile map. Tactile maps are complete or partial 3D-maps.


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Fig. 1: Two Relief maps of India as examples for a clear 3D Effect, thermoform. Source: blista e.V., (without year)

The development of the last 20 years was remarkable in practical and in theoretical regards. Nevertheless still much need for additional research exists. Many psychological problems of the perception of tactile structures and the formation of space conceptions by blinds and persons with low vision are not solved yet. Therefore different research projects exist (Perkins and Gardiner, 2003, Koch, 2007, Aldrich, 2008, Cryer, 2008 etc.).

2 State of the Art at the End of the First Decade of the 21st Century Overview reports to the state of tactile mapping have been given during the last years with different extent and different depth (Tatham 2003, Rowell 2007, Geiger 2008 etc.). The most recent information are published in the papers of the ICC Moscow in 2007 and the results of the conference “Tactile Graphics” (Birmingham 3-5- December in 2008). Within the last years new methods, technologies and devices have been developed. Nevertheless traditional (classical) and new tactile cartographic media co-exist. Traditional media are reliefs/models, tactile maps, tactile atlases (sections bound), tactile globes. New media are characterised by the application of computers, GIS, multi-mediality (audio-tactile dialogue systems), internet integration, real and virtual tactile displays, virtual tactile maps. In the widest sense also navigation systems with and without GPS application can be included.

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The current level of development should be characterised according to the following aspects: type of media, symbols and map design, production methods. 2.1 Type of Media Today the classical hand maps (single maps), atlases (map series) and globes are still getting produced. For single maps as well as for atlas maps a format of approx. 30 cm x 40 cm may not be exceeded according to the touch space of a hand (of the adult person). For children size should be smaller. Tactile wall maps remain rare until present. Sometimes they are used as orientation aids in stops of the public transport (format approx. 40 cm x 60 cm; König 1995). Tactile wall maps are also used as large-size city maps. In this case, the large format ( e. g. 4 m x 6 m, see Oberhammer, 1996) often leads to problems in map reading. Therefore, it is favorable to use these big city maps in the form of sections (parts). An international survey by Rowell and Ungar in 2002 yielded the following results (frequency of made media):

Fig. 2: Presentation forms of maps (% of respondents). Source: Rowell and Ungar, 2003.

One can remark, that even in the “age of the new media” the classical hand maps (single maps), atlases (sections bound, map series) and globes are still in use and production. Single maps predominate. They can be produced in a simple way and at a reasonable price in many copies.


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Fig. 3: A single map of Dresden (historic old town); micro-capsule paper method; source: Landeshauptstadt Dresden, 1995.

Identical to visual maps and as a function of the area displayed, the full range of scales is used. It must be observed, that the scale has to be at least twice as large as the one of a visually used map in order to convey nearly the same amount of information (see Koch, 2007). Today atlases are wide spread: World atlases, continent atlases, town atlases, national atlases. National atlasses depicts different subjects of one country (Mack, 2000). In Germany (Leipzig, Saxony) a large and modern collection of tactile atlases is produced, e.g., by the German Central Library for Blind People (Deutsche Zentralbücherei für Blinde, DZB) at Leipzig (Nordmann 2008, Deutsche Zentralbücherei für Blinde zu Leipzig). Also – for instance - in Poland, a comprehensive tactile atlas of Europe and a tactile school atlas are produced (2005, 2007). Today topographic – chorographic maps still predominate, but thematic maps increase in importance. Their problems have been examined in detail by S. Geiger (2001) in connection with the discussion of audio-tactile dialogue systems. Tactile globes exist in different diameters, with additional colour design and only as relief globes Classical tactile globes with 32 and 50 cm in diameter have been created in Germany during the 80s (Podschadli, 1986). Pardy (2003) has introduced a physio-topographic and a political globe for blind users. In the current product scope (2009) of the “Verein zur Förderung der Blindenbildung (VzFB)” – Association for the support of the blind person´s education – , Marburg, one finds a relief globe with additional contrasting colours, physically, 40 cm of diameter. The

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elevation data of the earth surface (raised relief) are determined from radar data SRTM (VzFB, 2009). For partially sighted geography students the American Foundation for the Blind (AFB, U.S.A., 2009) provides tactile world globes with 10´´ and 12 ´´ in diameter. Finally it should be noticed that the today´s so-called tactile hyperglobes are not genuine (real) tactile globes. They can be used only by sighted people. There are however considerations and ideas, to make them fit for blind and visually impaired persons in the form of tactile hyperglobes (Riedl, 2009).

Fig. 4: Detail of a tactile globe with relief and contrasting colours. Source: Zabala, 1996.

Within the new tactile cartographic media the audio-tactile dialogue systems have fully matured and have found entrance into the practical use. Virtual displays and virtual maps are further developed.


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Fig. 5: Virtual tactile Display See by Touch (Rieger, 2002), and Display VTPlayer TM (VIR TOUCH 2003) (colour version on CD-ROM)

2.2 Symbols and map design Already in the 90s of the last century a high level of knowledge was reached. This has positively influenced the practical production of tactile maps and its efficient use. A comprehensive standardisation of the tactile symbols and the use of symbols has not been reached yet. For this we can name several reasons. Thus, e. g., the choice of the symbolic system is depending on the production method, also the number of well discriminated symbols is limited. There are individual differences by the perception of symbols etc. Suitable and realistic is a unification of single map subjects and specific map types (town maps, physical basic maps for geography lessons, and the like). A System of general design rules was accepted (Lehmann 1990, Tatham 1991, 1999, Edman, 1992 and other). Extensive theoretical investigations partly led to new knowledge. Vasconcellos (1993, 1996) adapted the system of the visual variables (J. Bertin) for the field of the tactile maps. Geiger (2001) studied the possibilities and limits of the use of cartographic representation methods for thematic tactile maps. First connections and dependencies on structure and function (both categories in the widest sense) were extensively examinated also by Geiger (2008). Structure and function were also important aspects for the creation of a classification of tactile symbols by Rowell and Ungar (2003). Some newer experimental investigations (“cognitive tactualisation approach”) were concerned with the effect of the tactile variable elevation (Jehoel et al. 2009). For instance at the university of Surrey, Guildford (UK), studies were carried out on the optimal elevation in tactile maps. It turned out, that the symbol elevations necessary for identification are considerably lower than it would be expected on the basis of existing tactile maps (generally 0,5 mm or higher) and design guidelines. Tactile

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map production costs could be reduced and map durability increased by reducing symbol elevation (Jehoel, Sowden, Ungar and Sterr, 2009).

Fig. 6: Visual and tactile graphic variables; source: Vasconcellos 1996.

Rowell and Ungar (2003) have carried out an international poll to the use of tactile symbols. It appeared that an average of 10 until 15 distinct symbols per map are commonly used (6 point, 3-4 line, 3-4 area symbols). In official topographic maps for sighted users (such as the Ordnance Survey series or German Topographic Maps) these are between 50 an 100 symbols per map, with the proportions varying depending on the scale. The tactile maps which are also used for persons with low vision or with a rest of vision should be formed both with raised symbols and colourful surface. The colours must be forcible, saturated, and contrasting. Mack (1999, 1999 a) has carried out empiric investigations to the colour use in connection with the Swedish company METRIA. Mack has applied her colour system of tactile maps (atlas maps) of Sweden.


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Fig. 7: Left: a vegetation map of Sweden; source: Mack 2000. Right: thematic maps (variables form, texture, colour; extracts, thermoform). Source: Geiger (2008) (colour version on CD-ROM)

As a meta methodology for the investigation of the tactile map design two approaches are to be distinguished (Rowell, 2003): x Bottom-up perspective This approach considers the social context of tactile mapping, where users undertake tasks involving real world strategies, and where user preference and input takes precedence. x Top-down perspective Through experimental research model responses to tactile mapping are tested from a cognitive or perceptual perspective. Both approaches make important contributions to tactile map design. They are methodically disputed regarding their advantages and disadvantages (Tatham, 2003). The research methodology by Geiger (2008) could be called the third approach, namely a deductive approach. This methodology is also marked semiotical. However, it should be qualified by future empirical studies. 2.3 Tactile Production Methods Presently, in principle all maps for blind and visual impaired people can be produced automatically or partially automatically. Therefore the following technologies are used (with different frequency):

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x Thermoform (Vacuum Forming), x Micro-capsule (-paper) and fuser, These technologies are the two most popular production methods. x Embossing, x Tactile Printing, x Other. An international survey and a literature analysis by Rowell and Ungar (2003) yielded the following percentages:

Fig. 8: Tactile production methods used (% of respondents). Source: Rowell and Ungar, 2003. Herein also proved: Thermoform and micro-capsule technology today are important methods.

The computer-aided production of the layout delivers as a rule an intermediate product. It is generalised according to his scale und function. Michel (2000) from the Magdeburg University has developed a procedure for the interactive generalisation, which he has also practically tested. Fully automatic solutions are hardly feasible because too many influencing factors and the individual physical conditions of the map users must be considered. By making use of the micro-capsule technology (so-called swell paper) printing is effected in 2D and the result is heated in an fuser (“enhancer”, a infra-red source). Within the scope of the thermoform technology, the digital tactile map is automatically transformed into control commands for a CNC milling machine. With its help a negative model is generated, which is used as a mould (“master”) for the vacuumforming of the 3D-map. The technologies which are used at the company METRIA in Sweden are state of the art.


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In Slovenia a data bank with map layouts has been built up for tactile maps in different scales. Rener (2008) describes the automated process of production of maps with the latest 3D printing technology. Since 2000 is the non-impact printer PRINT on the market. The map editing takes place by means of graphics software (graphics packages), e.g., OCAD, FREEHAND and other. The tactile map is printed with a wax-ink-jet plotter (Mack, 2000). Mc Callum, Rowell and Ungar (2003) described a new method for producing tactile maps and diagrams using the piezoelectric inkjetting. In order to produce maps, a photo-curing acrylic polymer ink is repeatedly printed onto a thermoplastic substrate and exposed to ultraviolet light which bonds the ink to the substrate and forms to a solid surface.

Fig. 9: Novel tactile printing machine. Source: McCallum et al., 2003.

It can be expected that in the future the portion of the maps which have been produced by means of relief printing will increase.

3 Current projects, novel methods Today, with the help of novel technologies, the internet can also be used. Particularly since 2007 many new results were published (Marston and Miele, 2007). Also the practical use of these technologies is in its initial state. At the ICC in Moscow, Miele (2007) has presented the project TMAP, using GIS in conjunction with embossing technologies to allow blind individuals to independently produce high-quality street maps for their use in way-finding. The number of the new systems is very large.

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Fig. 10: New tactile cartographic media - chronological development. Source: Geiger, 2008.

Of the right side is significant that since 1995 many new systems of virtual tactile displays and some virtual tactile maps were developed. In particular, a project with the name FuSe is promoted by the ICA Commission on Maps and Graphics for Blind and Partially Sighted People. The FuSE system strictly speaking leverages novel cartographic conventions and technological interface innovations to render maps and geographic information in a usable non-visual format. These components include: user tested non-visual data symbolisation strategies; authoring tools designed to enhance the output of geography software products; a dynamic magnetic tactile “display” surface; infra-red hand tracking for scene exploration in lieu of traditional hand-held computer peripherals; and a non-visual user interface that functionally separates control and exploration channels (University of Calgary, Department of Geography; Douglas Hagedorn, Dan Jacobson, 2009). A new research project of the Hamburg University, which was initiated in 2008, treats problems of way-finding and orientation by means of multimodal maps. A specific type of maps was developed, the You-are-here map (YAH map). It is a bimodal tactile-visual map including both, colour print for sighted people and embossed relief for visually impaired persons (Graf, 2008). YAH maps present an abstraction of the „

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environment at the current location in the world with a clear marking of the map readers´ own position (see www.maps4vips.info, Habel & Graf, 2008). Within this project also audio-tactile YAH maps for visually impaired people will be developed and tested. The Chairman of the Commission on Maps and Graphics for Blind and Visual Impaired People, Dan Jacobson, sees (2007) the future of tactile cartography in the use of multimodal dynamic computer interfaces. And its predecessor, Jonathan Rowell, asks in a contribution for the ICC 2007: “The end of tactile mapping or a new beginning – LBS for visually impaired people? […] Will electronic devices ultimately replace conventional tactile maps?” (p. 363). Future interdisciplinary research will answer these and other questions.

References Aldrich, F. (2008): `Cognitive complexity` versus `perceptual complexity in tactile graphics. Abstract P4-C, NCTD Conference 2008, Birmingham, UK. Cryer, H. (2008): Exploring tactile graphics – wich strategies work? Abstract P8B, NCTD Conference 2008, Birmingham, UK: Edman, P.K. (1992): Tactile Graphics. The American Foundation for the Blind, New York. Habel, C. and Graf, C. (2008): You-are-here Maps as Navigation Aids for Visually Impaired People. In: Klippel, A. & Hirtle, S.: Workshop Proceedings “You-are-here Maps”, pp.1-10. Spatial Cognition 2008. September 15-19, 2008. Freiburg/Breisgau, Germany. Geiger, S. (2001): Untersuchung zur Herstellung und Nutzung thematischer Karten mit Hilfe eines audio-taktilen Systems . Diplomarbeit (Master Thesis), TU Dresden. Geiger, S. (2008): Untersuchungen zur Struktur und Funktion taktiler kartographischer Medien und ihre Wechselwirkungen. Dissertation TU Dresden. Graf, C. (2008): From Interaction between Language and Visual Representations to the Interaction between Language and Haptic Representations. Presented at the Workshop on the Interaction of Vision and Language in Cross-Modal Comprehension, CINACS Summer School 2008, 08-12 September, 2008. Hamburg, Germany Jacobson, D. (2007): The Future of Tactile Cartography: From Static Raised Lines to Multimodal Dynamic Portable Computer Interfaces. In: Abstracts of Papers. XXIII International Cartographic Conference, 4-10 August, Moscow 2007, Russia, p. 358. Jehoel, S., Sowden P.T., Ungar, S. and Sterr, A. (2009): Tactile Elevation Perception in Blind and Sighted Participants and Its Implications for Tactile

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Map Creation. In: Human Factors: The Journal of the Human Factors and Ergonomics Society. Vol. 51, No. 2, pp. 208-223 Koch, W. G. (2007): Kartographische Informationen tasten und hören – Orintierungshilfsmittel für Blinde. In: Koch, W. G. (2007): Beiträge zur wissenschaftlichen Kartographie. Contributions to scientific cartography. Dresden, pp. 234-242. König, V. (1995): Wandreliefkarten. In: Taktile Medien. Tagungsband. Freital/Dresden, pp. 109-112. Krauze-Tomczyk, I. and Karpinska, J. (2007): “Geographical Atlas of Europe” for the Blind and Visually Impaired. In: XXIII International Cartographic Conference, Moscow, Abstracts of Papers, Moscow, pp. 57-58. Lehmann, K. (1990): Handbuch des taktilen Kartenbaus. Forschungsbericht Sozialforschung. Hamburg. Mack, D. (1999): Entwicklung eines Farbsystems zur Anwendung in Karten für Sehgeschädigte. Studienarbeit (Student Research Paper), TU Dresden Mack, D. (2000): Untersuchungen zu einem taktilen Atlas von Schweden. Diplomarbeit (Master Thesis), TU Dresden. Marston, J.R. and Miele, J. (2007): Large Print Map Automated Production. In: Abstracts of Papers. XXIII International Cartographic Conference, 4-10 August, Moscow 2007, Russia, p. 361. McCallum, D., Rowell, J. and Ungar, S. (2003): Producing Tactile Maps Using New Inkjet Technology: an Introduction. In: The Cartographic Journal, Vol. 40, No. 3, pp. 294-298. Michel, R. (2000): Interaktiver Layoutentwurf für individuelle taktile Karten. Aachen. Nordmann, A. (2008): Relief techniques in the DZB and the newest project “world atlas” in two languages. Abstract P6-B, NCTD Conference 2008, Birmingham, UK. Pardy, D. (2003): Topographic maps to Support Courses for Visually Impaired Students. In: The Cartographic Journal, Vol. 40, No. 3. pp. 288-291. Perkins, C. and Gardiner, A. (2003): Real World Map Strategies. In: The Cartographic Journal, Vol. 40, No. 3, pp. 265-268. Podschadli, E. (1986): Blindenkarten und ihre Herstellung. Kartographische Miniaturen, Nr. 8, Berlin. Rener, R. (2008): An automated procedure for production of tactile maps with 3D printing technology. Abstract P10-C, NCTD Conference 2008, Birmingham, UK. Riedl, A. (2009): Taktile Globen – die nächste Stufe der Globenevolution? In: Kriz, K., Kainz, W. & Riedel, A. (Eds.): Geokommunikation im Umfeld der Geographie (Wiener Schriften zur Geographie und Kartographie, Bd. 19), Wien, pp. 176-183. Rowell, J. (2003): Guest Editorial Tactile Mapping, In: The Cartographic Journal, Vol. 40, No. 3, pp. 219-220. Rowell, J. and Ungar, S. (2003): A Taxonomy for Tactile Symbols: Creating a Useable Database for Tactile Map Designers. In: The Cartographic Journal, Vol. 40, No. 3, pp.273-276.


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Rowell, J. and Ungar, S. (2003): The World of Touch: Results of an International Survey of Tactile Maps and Symbols. In: The Cartographic Journal, Vol. 40, No. 3, pp. 259-264. Rowell, J. (2007): The End of Tactile Mapping or a New Beginning: LBS for Visually Impaired People. In: Abstracts of Papers. XXIII International Cartographic Conference, 4-10 August, Moscow 2007, Russia, p. 363. Tatham, A. F. (1991): The design of tactile maps: theoretical and practical considerations. In: Mapping the Nations. Proceed. of the 15th Internat. Cartograph. Conference, Bournemouth, Vol. 1, pp. 157-166 Tatham, A. F. (2003): Tactile Mapping: Yesterday, Today and Tomorrow. In: The Cartographic Journal, Vol. 40, No. 3, pp. 255-258. Vasconcellos, R. (1993): Representing the geographical space for visually handicapped students: a case study on map use. 16th International Cartographic Conference Proceedings, Vol. 2, Köln, pp. 993-1004. Vasconcellos, R. (1996): Tactile Mapping Design and the Visually Impaired User. In: Wood, C.H. and Keller, C.P. (Eds., 1996): Cartographic Design, Theoretical and Practical Perspectives. Chichester, New York, Brisbane, Toronto. Zabala, K. C. (1996): Funding aid for Latin America. In: The World Blind, No. 13, July 1996, La Coruña, pp. 17-18.

Hypsometry in Tactile Maps

Vit Voženílek, Veronika Růžičková, Dita Finková, Libuše Ludíková, Zuzana Němcová, Jan Doležal, Alena Vondráková, Magdaléna Kozáková, Vojtěch Regec Department of Geoinformatics, Palacký University Olomouc, Olomouc, Czech Republic

Abstract People either perceive geospace directly through their senses or their perception is mediated via geo-information. Those who are blind or visually impaired have to fight difficulties in perceiving geospace. It is one of the tasks of cartography to provide these people with suitable devices to perceive and study geospace. Modern tactile maps enable perception of geospace in a highly illustrative way. The hypsometric map of Europe created at the Palacký University in Olomouc as part of a development programme can serve as an example. These maps are unique three-dimensional tactile maps that enable people with visual impairment make use of residual vision and blind people use Braille. Three-dimensional imaging represents a revolutionary approach to tangible geospace representation. The resulting product is a three-dimensional model with discrete hypsometric layers, with Braille writings and with contrasting colours that distinguish it for people with visual impairment. The hypsometric map of Europe is unique thanks to its processing technique. Its illustrative character provides more information to people with visual impairment than what had been possible to date. Keywords: elevation, tactile maps, 3D printing, Braille, perception, blind persons M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_10, © Springer-Verlag Berlin Heidelberg 2012

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154 Vit Voženílek, Veronika Růžičková, Dita Finková, Libuše Ludíková, Zuzana Němcová, Jan Doležal, Alena Vondráková, Magdaléna Kozáková, Vojtěch Regec

1 Introduction Today’s modern information society offers innumerable possibilities to visualise geospace with the use of state-of-the-art information technologies. Geospace (geographical space) is that part of landscape sphere which is delimited by the influence of human activity on its natural elements. Vertically, asthenosphere (the liquid region of the upper mantle on which litospheric plates move) is the lower boundary of geospace, outer troposphere, where the majority of meteorological phenomena take place, is the upper boundary of geospace. Thus delimited geospace is either perceived by people directly through their senses or their perception is mediated via geo-information (geographical information, spatially localised information). The perception of geospace is a prerequisite for everyday practical life anywhere on Earth, as well as for cognitive processes related to how natural and social phenomena (objects and processes) function. Those who are blind or visually disabled have to fight difficulties in perceiving geospace. It is the task of cartography to provide these people with suitable devices to perceive and study geospace. The first tactile maps coming from the 1980s served for practising orientation in space and independent movement and contained primarily line representation of people’s movement routes in their daily life (e.g. the journey from home to work or shopping facilities). They were made of embossed foils produced by special vacuum printers. However, these maps served as a mnemonic aid rather than a tool for the presentation of geospace. Only relief maps primarily designated for people without any visual impairment could be considered an actual approximation to real space. These gave the sense of the Earth's surface topography to blind people but were not able to provide further geographical information (occurrence of point phenomena – e.g. cash machines, course of line phenomena – e.g. railway corridors, distribution of surface phenomena – e.g. conservation zones, etc.). Cartographically developed countries provide their visually impaired citizens with a wide selection of publications with geographic information, including top-quality equivalents of tactile national atlases. The Palacký University in Olomouc has undertaken a development programme which will enable blind and visually impaired people to perceive geospace thanks to modern tactile maps. With the use of state-ofthe-art technologies three-dimensional maps are created and a unique processing technique makes it possible for visually impaired persons to perceive geospace in a most illustrative way. These are unique three-


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dimensional tactile maps that enable visually impaired people to use their residual vision and blind people to use Braille.

2 Need of three-dimensional cartography for the visually impaired Visually disabled people constitute a relatively large group. Currently, there are no accurate statistics on the number of visually disabled people, neither for the Czech Republic, nor for the whole world. The British Royal National Institute of Blind People (RNIB) estimates that the share of visually impaired people could be 1.5–2 percent of the world's population. This would mean that there are up to 150,000 visually impaired in the Czech Republic. A visually impaired person is a person who keeps having problems with their eye-sight in their daily life even after vision correction. Sensory deficit, loss or significant decrease of visual perception markedly influence all elements of everyday life and pose noticeable constraints in daily life (Gardiner 2001, Greenspan, Bolanowski 1996). 2.1 Spatial orientation of the visually impaired Orientation in space and independent movement belong among the areas most influenced by severe visual impairment. Independence during spatial orientation is a key skill that has to be acquired by visually disabled people and it is generally considered part of their spatial literacy (Gibson 1968 Bentzen 1973). Such independence directly influences their quality of life and, to a certain extent, even the success of their social integration. Currently, the so called complex approach is being preferred in terms of orientation in space, i.e. the use of information and communication technologies. Tactile and auditory training should be considered an integral part of this issue. Tactile information and experience have a vital role in spatial orientation. Knowledge of the local area, of the planet as a whole and its surface (including altimetry), of the person's direct environment and daily routes can be acquired thanks to special maps designated for visually disabled people (Wiedel, Groves 1969, Theissen 2000, Ungar, Jehoel, McCallum, Rowell 2005). Thanks to orientation in the local area the person achieves more complex understanding of geospace. Moreover, it is certain that orientation in tactile maps and diagrams can further lead to the fact that the


notions acquired are more accurate, are acquired with higher certainty and correspond more to the real environment (LaMotte, Whitehouse 1986, Lederman 1974, Lobben 2005, Nolan, Morris 1971, Perkins, Gardiner 1997). Development of competence related to spatial orientation is anchored in the Czech schooling system via a special framework education programme for primary education, especially as part of the subject called "Spatial orientation and independent movement of the visually disabled", but also in subjects like physical education. Those who lost their sight after finishing their education can complete basic spatial orientation and independent movement training in in-house and outpatient facilities for visually disabled adults (Rowell, Ungar 2005). Orientation in tactile relief maps is part of spatial orientation training at schools and in the above mentioned facilities, following the needs and wishes of the students and clients. 2.2 Use of cartography for orientation in geospace One of the most serious consequences of visual disability is the necessity to learn to orient ourselves in our environment with or without significantly limited visual information, which is related to the need to perceive geospace and acquire notions about it using other senses. To be able to acquire a correct notion of the environment it is necessary to walk through the place several times and receive spoken information about it from a guide or an instructor, as well as use a map or a diagram to find out about the arrangement of the geospace, the distance between the objects or the shapes of the buildings, for example. Since the beginning of education of blind people and people with severe visual impairment, their instructors and teachers have tried to transfer space onto a surface using various techniques, mostly by wax or plasticene engraving, attaching waves and wires to felt, embossing foils or paper, or creating thermovacuum films or paper models. However, the majority of these techniques are used to create two-dimensional works which provide information about the spatial arrangement of objects and distance between them but do not provide any information about their characteristics, e.g. height of buildings, depth of valleys or type of forests. The modern cartography can create three-dimensional maps, offering much more than simple spatial relations between individual real objects represented on the map. It also provides information about their characteristics, including the third dimension. Three-dimensional


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cartography enables the creation of illustrative spatial notions using the touch and all its functions (depth, roughness, structure, etc.).

Fig. 1. Existing tactile aids – plastic maps of the Czech Republic.

3 Hypsometry in maps Throughout centuries cartographers have had to tackle various problems when trying to transfer three-dimensional geospace onto a map (Kozáková, Voženílek 2009). Representation of land elevation (hypsometry) has been the most difficult task related to the user’s imagination. To represent the altimetry of geospace the third dimension (land elevation) needs to be present directly in the map. As in the field of cartography developed, a high number of cartographic methods of altimetry representation were established. The earliest is the so called hill method, followed by the hatch method. Currently, the most often used are the contour line, shading and colour hypsometry methods (Veverka 2004, Voženílek 2001). The colour hypsometry method allows easy orientation in the elevation of geospace and leads to a good spatial notion of hypsometry. This method is based on the contour line method (contour line – imaginary line that joins points of equal elevation on the Earth’s surface). Colour hypsometry


consists in the depiction of contour lines that delimit selected height intervals and colouring the surface delimited by the contour lines with adequately selected shades (Pravda 2006, Kraak, Ormeling 1996). Hypsometric colour scale uses a range of colours arranged according to a certain principle (Voženílek 2001). The most frequent approaches abide by the following principles: "the higher, the darker" (the greater the elevation, the darker the colour of the layer), "the higher, the lighter"; the most wellknown is the Sydow-Wagner scale (the colour sequence from the smallest to the greatest elevation is the following: green – yellow-green – yellow – yellow-brown – orange-brown – brown – brown-red). Colour hypsometry is used to represent hypsometry in the majority of general geographic maps for the public and for schools (school atlases and wall maps), with the convention of using green to represent lowland, yellow to represent medium elevation and brown to represent high elevation (Fig. 2e).

Fig. 2. Cartographic methods to represent hypsometry a) hill, b) hatch, c) contour line, d) shading, e) colour hypsometry.

4 Three-dimensional imaging techniques Three-dimensional imaging represents a revolutionary approach to tangible geospace representation. Three-dimensional objects are printed from


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a three-dimensional computer model (processed by GIS), not by the method of lathe-turning but by applying layers of 0.1mm of gypsumpowder-based material and binding agent which can be of different colours thanks to the traditional ink printer technologies. Three-dimensional imaging and printing was time-consuming and uneconomical up to now but thanks to this technology it has become much more accessible. The three-dimensional computer model facilitates editing as well as bulk printing (Kozáková, Voženílek 2008). Print programme divides three-dimensional computer models into thin layers. A layer of gypsum powder is placed in the corresponding printer compartment; the thickness of the power is determined by the thickness of the calculated layer. A special adhesive agent of a required colour is applied over it, but only in the place of the image. After finishing the map and applying adhesive on the last layer the un-glued powder is removed from the places where "there is no map". The printer and the printing procedure as such are relatively expensive but there are no constraints as to the number of objects in the threedimensional computer model. The only constraint is the size of the print. The maximum size supported by the printer used is 254×356×203mm and the thickness of one layer ranges from 0.089 to 0.203 mm. However, considering how fast this technique is improving we can suppose that at the end of the project period there will be a one hundred percent improvement in the described parameters. Nevertheless, the current size is suitable to meet the accepted criteria of tactile maps, i.e. maximum width 55 cm, length for bimanual perception 105 cm, length for monomanual perception 75–80 cm.


Fig. 3. Contex 3D printer.

5 Hypsometry discretisation to create hypsometric tactile map of Europe The use of some of the above mentioned cartographic methods (Fig. 2) to create georelief in tactile maps is not possible because of the degree of abstractness and because there are great requirements of the users' imagination about the three-dimensional space based on the visual perception of the map image (Voženílek 2005). So called plastic maps seem to be the best solution for representation of hypsometry in tactile maps. These are three-dimensional maps designated for common users with shaped hills, valleys and other forms of the Earth's surface. In the case of plastic maps designated for visually disabled people it is suitable to represent hypsometry incontinuously and use colour hypsometry, so that individual elevation levels are differentiated not only by colour (for users who use residual vision) but, more importantly, by the level of elevation. Discretisation (use of incontinuous representation instead of a continuous one) and elevation above the basic level of the tactile map makes understanding of hypsometry in tactile maps easier. Generally, when using colour hypsometry, first an elevation scale is used, and only then hypsometric colour scale is determined. The number of elevation levels is usually based on the elevation difference between the highest and the lowest points in the region. Usually, 6 to 10 elevation levels are used, with linear or non-linear increase. Scales that grow


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exponentially are usually used to represent land because they correspond the distribution of elevation of the Earth's surface best. We recommend the scales of 0 - (50) - 100 - 200 - 500 - 1,000 - 2,000 - 4,000 and more metres above sea level. To represent hypsometry in the map of Europe we used a digital altimetry model available from the ESRI Data & Maps dataset supplied with the ArcGIS 9.x software, whose accuracy (horizontal and vertical) is suitable for the creation of hypsometry in a tactile map of Europe. The data were processed in ArcGIS 9.x to get a polygon layer, where individual polygons include areas with elevation divided into four elevation intervals: x 0–500 m above sea level; x 501–1,000 m above sea level; x 1,001–2,000 m above sea level; x more than 2,000 m above sea level. These four levels were chosen to reach the best ratio of the information given and its comprehensibility. With more intervals (elevation levels) there is a significant decrease of the users’ ability to correctly match the elevation level with a key symbol. General geomorphological classification of georelief was respected and the resulting intervals were rounded, so that the range of elevation is easy to remember. Apart from elevation the attribute table of vector layer of elevation levels also contains information about polygon colours. Using this information each polygon was assigned a third dimension, colour and possible relief hatch in the 3D printer software. The elevation of hypsometric level (Fig. 4) was discussed for various values, the value of differences between the elevation intervals of 0.5 cm was chosen for the print of the testing sample of the hypsometric tactile map of Europe. The width of hypsometric levels remained a variable quantity. An additional dotted relief texture was used to mark the Czech Republic on the first version of the map in order to provide information about the elevation of the Czech Republic and to facilitate orientation in the map. The hypsometric tactile map of Europe printed by a 3D printer was submitted for testing and assessment by blind and visually impaired people in cooperation with primary and secondary schools for pupils with visual disabilities and with organisations that help adults with visual disabilities in the Czech Republic, as part of the project "Perception of Geospace by Means of Modern Tactile Maps".


Fig. 4. Constant elevation (a) and inconstant elevation (b) of hypsometric levels.

6 Colour differentiations for people with residual vision Tactile maps can have more uses for people with visual disabilities. They do not necessarily have to be used only by the blind but can also be used by the purblind and those with residual vision (Amick, Corcoran et al. 1997). Use by pupils of primary and secondary schools during geography lessons is especially desirable. Tactile maps designated for the visually disabled have a special colour scheme, so that they can be used by the purblind. The selected colours have a high contrast, so that they are easily distinguishable by sight; at the same time, they approximate the principle of colour hypsometry. Lowland is depicted in green while the highest elevations in Europe (the Alps, the Pyrenees) are the darkest places on the map – depicted in black. The other colours used for hypsometric levels are yellow and magenta. The selection of colours is not random. Testing (see below) showed that the selected colours are suitable for the purblind. They have sufficient contrast and the users labelled them suitable. Subtractive colour differentiation of elevation levels used: x interval 0–500 m above sea level green CMYK (40%, 10%, 100%, 0%) x interval 501–1,000 m above sea level yellow CMYK (0%, 0%, 100%, 0%) x interval 1001–2,000 m above sea level magenta CMYK (0%, 100%, 0%, 0%) x interval more than 2,000 m above sea level black CMYK (0%, 0%, 0%, 100%)


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x ocean in white (after users’ comments concerning the first version, the ocean is differentiation by relief hatch in the final version, which is important for clear distinction between the land and the sea) Apart from differentiation of elevations in five levels blind people can make use of further surface finish of the map. The seas around Europe are distinguished from land by relief hatch. The map key is in Braille and in black print for the purblind. The whole surface of the map is finished with a special layer that prevents erosion of the powder used for the creation of the map. This leads to better conservation of the map and, at the same time, respects the principles of visual hygiene according to which people with visual disabilities should not be exposed to dusty environments or work with dusty materials.

7 User perception of hypsometry in tactile maps People with visual disabilities must perceive depth (and possibly height) during their daily movement on routes. Unfortunately, cartographic investigation stands only at the beginning of a long journey of studying perception of depth and height in maps.

Fig. 5. Hypsometric tactile map of Europe in software processing


The testing of the hypsometric tactile map of Europe was performed on three levels, taking into account time, and the experience and age of the persons tested. Therefore, the map key and the draft maps were tested in primary and secondary schools, as well as in organisations for adults with visual disabilities (Růžičková et al. 2009). The research sample consisted of 27 secondary school students aged 16– 20 (2 students with severe purblindness, 1 with deafblindness, 24 with blindness (out of which 9 girls)), 5 primary school students with blindness aged 12–17 (out of which 3 girls) and 4 adult users in an organisation for adults with visual disabilities (2 men with residual vision, 1 blind man and 1 blind woman). The following findings based on testing, interviews and observation were reached: Positive reaction to tactile map and pros of tactile map: x Map key was considered transparent and was evaluated as beneficial. x Users used four basic levels to find elevation in Europe. Till now the students have not had the possibility to get a notion of the distribution of mountain ranges and compare them respective to the European states, etc. x Colours of hypsometric levels help users with residual vision (with severe purblindness) to orient in the map. x Very positive evaluation was based primarily on the fact that before there had not been a tactile map that would help the users develop the notion of orography of Europe or its states. x x

x x

Limitations of tactile map: The delimitation of the Czech Republic is deficient because it is impossible to find by touch in the mountainous regions (only with the teacher’s help). Users had problems with orientation in the map when finding states because they had not used such a tactile map or a similar one before and, therefore, they were unable to determine the location of the states. Students expressed their wish to distinguish where one state ends and another one begins (students only knew "two-dimensional" maps with states differentiated by borders). 28 percent of users had problems distinguishing elevation levels when the elevation levels were situated on more distant parts of the map. Students with residual vision had a problem distinguishing yellow and orange in the first version of the map.


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x It is convenient to make relief distinction of the sea (comment concerning the first version of the map) in order to facilitate reading of the first hypsometric level and the shore line of Europe.

Fig. 6. Testing of the map by a blind user.

8 Findings and conclusion Tactile maps that are currently being developed as part of the development programme at the Palacký University in Olomouc are unique in terms of the technique used. They enable visually disabled people to perceive geospace in a different way than in the case of traditional tactile maps while rendering more information than the traditional ones thanks to their illustrativeness. Up to now, hypsometry was presented to the visually disabled usually via plastic relief maps. However, these are primarily designated for people with no visual disabilities and are only able to provide information about the segmentation of the Earth’s surface to the visually disabled, not about the distribution of geographical information, including the dimension of height or the real elevation. Discretisation of hypsometry into elevation levels above the basic level not only facilitates understanding during the study of hypsometry in tactile


maps but also enables the inclusion of description, and possibly other information in the map. The number of elevation levels is a discussed quantity. Generally, we can say that it depends on the map’s purpose. To create a map suitable for a wide group of users we recommend four hypsometric levels with the height of 0.5 cm because such a solution contains the best ratio of the information provided and its comprehensibility. To make the map suitable even for the purblind we differentiated the levels not only with description in Braille but also in black print with contrasting colours. During the testing of the hypsometric map of Europe we took into account the time, and the experience and age of the persons tested. The majority of negative comments were related to the fact that no similar map had been available in the Czech Republic and the users were inexperienced in working with the new tactile map. The map key and contrastive colours which facilitate orientation to the purblind were evaluated as beneficial. On the other hand, the users had orientation problems when finding states. The users’ comments were used to re-create the hypsometric map of Europe, adding an overview map of states and relief hatch for the seas, as well as modifying some other parameters, so that the map better suits the users’ needs. The map was appraised especially by the teachers of visually disabled students because no other alternative existed up to now. The specifications of the hypsometric map of Europe do not differ for students and adults. Students are more experienced in using tactile maps thanks to their school education, adults and seniors have little experience. Therefore, it is often necessary to use personalised approach to acquaint the teachers with the map and help them with orientation in space. Because an entirely new technology was used for the creation of the hypsometric map of Europe the teachers first have to be shown how to use the map correctly and acquainted with the advantages of the map, and then users need to repeatedly practice using the map. Increasing integration of the visually disabled into daily life brings about an increasing need of tactile maps. Modern tactile maps must be distributed to schools and organisations for people with visual disabilities and made generally accessible, so that the visually disabled can use them often and without any difficulties. In the future, experience and further needs could lead to the creation of maps that would meet particular needs of individual institutions. Spread of tactile maps and their multifunctional use could lower their production costs and make them more easily accessible to all target groups. Future tactile maps could include an automatic voice or tactile output, orientation maps of areas available on public places could become commonly available.


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Fig. 7. Final version of hypsometric tactile map of Europe.

References Amick N, Corcoran J (et al.) (1997) Guidelines for design of tactile graphics [online]. New York, American Printing House for the Blind [http://www.aph.org/edresearch/guides.htm] Bentzen B (1973) Sites, Perception and the Non-visual Experience. In Kidwell, Clarke CR (1993: Introduction to Thermoforming 3: Vacuum Forming. Ammanford, Dyfed, C.R.Clarke & Co. Ltd. [http://www.crclarke.co.uk/] Edman PK (1992) Tactile Graphics. New York: American Foundation for the Blind. Finková F, Růžičková V (2009) Improvement in Spatial Sensation for persons with visual impairment through the medium of tactile / Braille maps. In Specjalne potrzeby edukacyjne. Tom 1. Bielsko – Biala: WSA Gibson JJ (1968) The Senses Considered as Perceptual Systems. London, George Allen and Unwin Ltd. Greenspan JD, Bolanowski SJ (1996) The psychophysics of tactile perception and its peripheral physiological basis. San Diego, Academic Press: 25 – 104 Hirn H (2005) Tactile maps for preschool children: the curriculum. Proceedings of XXII International Cartographic Conference A Coruña 2005 Jehoel S, Dinar S, McCallum D, Rowell J, Ungar S (2005) A scientific approach to tactile map design: minimum elevation of tactile map symbols. Proceedings of XXII International Cartographic Conference A Coruña 2005 Jesenský J (1988) Hmatové vnímání pomocí tyflografiky. SPN, Praha.

168 Vit Voženílek, Veronika Růžičková, Dita Finková, Libuše Ludíková, Zuzana Němcová, Jan Doležal, Alena Vondráková, Magdaléna Kozáková, Vojtěch Regec Kozáková M, Voženílek V (2008) Současné technologie tvorby hmatových map. In Feranec J, Fencík R (ed) Aktivity v kartografii. Zborník referátov zo seminára, Kartografická spoločnosť SR, Geografický ústav SAV Vydavatelství SAV, Bratislava Kozáková M, Voženílek V (2009) Thematic information in tactile maps. Kartografické listy, 2009 (17): Kraak MJ, Ormeling FJ (1996) Cartography: Visualization of spatial data. Addison Addison Wesley Longman, Harlow, Essex LaMotte RH, Whitehouse J (1986) Tactile detection of a dot on a smooth surface: peripheral neural events. Journal of Neurophysiology, 56 (4): 1109 – 1128. Lederman SJ (1974) Tactile roughness of grooved surfaces: the touching process and effects of macro- and micro-surface structure. Perception and Psychophysics, 16 (2): 385 – 395 Lobben AK (2005) Identifying the needs of tactile map makers. Proceedings of XXII International Cartographic Conference A Coruña 2005 Nolan CY, Morris JE (1971) Improvement of Tactual Symbols for Blind Children. Final Report, Washington, DC, Department of Health, Education and Welfare. Perkins C, Gardiner A (1997) "What I really, really want": how visually impaired people can improve tactile map design in ICC 97. Proceedings of 18th ICA/ACI International Cartographic Conference: Stockholm, Sweden, 23-27 June 1997: 1159 – 1166 Pravda J (2006) Metódy mapového vyjadrovania, Klasifikácia a ukážky. VEDA, vydavaťelstvo Slovenskej akadémie vied, Bratislava Rowell J, Ungar S (2005) Feeling our way: Tactile map user requirements – a survey. Proceedings of XXII International Cartographic Conference A Coruña 2005 Růžičková V, Stejskalová K, Ludíková L, Finková D, Voženílek V, Kozáková M, Šťávová Z (2009) Orientation and mobility of persons with visual impairment in the Czech Republic within the context of an evolving Europe. In Conference report. ICEVI 2009, Dublin Theissen N (2000) Computer-aided Tactual Graphics (Getting Started…). Enfield, Royal Blind Society. Ungar S, Jehoel S, McCallum D, Rowell J (2005) „Tactualization“ of spatial information: towards a perceptual-cognitive approach to tactile map design. Proceedings of XXII International Cartographic Conference A Coruña 2005 Veverka B (2004) Topografická a tematická kartografie 10. Vydavatelství ČVUT, Praha Voženílek V (2001) Aplikovaná kartografie I - tematické mapy. Univerzita Palackého v Olomouci, Olomouc Voženílek V (2005) Cartography for GIS – geovisualization and map communication. Univerzita Palackého v Olomouci, Olomouc Wiedel JW, Groves PA (1969) Tactual Mapping: Design, Reproduction, Reading and Interpretation. Washington, DC, Department of Health, Education and Welfare

Physical 3D models from LIDAR data as tactile maps for visually impaired persons

Friederike Schwarzbach1,2, Tapani Sarjakoski1, Juha Oksanen1, L. Tiina Sarjakoski1, Suvi Weckman1 1

Finnish Geodetic Institute, Department of Geoinformatics and Cartography, Masala, Finland 2 Institute for Cartography, Dresden University of Technology, Dresden, Germany

Abstract The paper describes the creation of a physical 3D model representing the Solvalla recreation area in South Finland. The data processing part includes the extraction of elevation models and other topographic features from LIDAR data and aerial photographs as well as steps to stack up the separate layers to the digital model suitable for the 3D printing. The present prototype is directed at the special needs of visually impaired persons. This influences the design of topographic objects such as roads and paths, the representation of certain areas such as water bodies and the choice of the colours in the model. The printed 3D model is used in a small user test with visually impaired persons. Keywords: airborne laser scanning, 3D cartography, 3D map, 3D print, haptic maps, landscape model, VRML


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170 Friederike Schwarzbach, Tapani . Sarjakoski, Juha Oksanen, L. Tiina Sarjakoski, Suvi Weckman

1 Introduction and Related Work The paper presents a study of the creation of physical 3D landscape models using rapid prototyping technology. In comparison with 2D maps and virtual 3D models, physical models have a number of advantages. First, they enable an easier perception of the landscape, especially for persons that are not familiar with map reading. Second, they offer an opportunity for a tactile experience. Finally, they are descriptive and can be used for promotional purposes, or as a support for decision making in urban planning. In the study presented in this paper, data from an airborne LIDAR (Light Detection and Ranging) system in combination with digital orthophotos are used as source data to create a 3D model of the landscape. The derivation of digital elevation models (DEM), digital surface models (DSM) and further digital models (e.g. tree crown models) from airborne laser scanning (ALS) data is a widely used practice. Furthermore, detection and vectorization methods for objects such as buildings, power lines, or trees from LIDAR data are under development or even implemented in practical applications (e.g. Ahokas et al. 2005; Maas 2005; Hyyppä et al. 2006; Soininen and Korpela 2007). The use of rapid prototyping for cartographic 3D models is described by Rase (2007, 2009). Besides the technical aspects of 3D printing methods, he illustrates several examples in his papers. He uses shapefiles as source data for the models, and surfaces are formed by small coloured triangles. Linear structures are defined as cubes, and extruded true type character definitions (glyphs) are used to include texts. Both linear structures and texts are again constructed from tiny triangles. While Rase mainly points out the usefulness of such physical 3D models for demonstrative purposes as well as for decision makers and other users with little cartographic background, he also mentions the potential of the technique for the creation of tactile maps for visually impaired people. An extensive study of theoretical aspects of tactile cartographic media is described in Geiger (2007). She investigates the structure and functions of tactile cartographic media as well as interactions between them. She also develops a taxonomy including traditional and new tactile media types. Voženílek et al. (2009) investigate the perception of the geographic space by means of three types of tactile maps that are all coloured 3D prototypes. While two of these map types are tactile relief maps using Braille letters, the third type includes sound activated by touching the map surface. Both publications, Geiger and Voženílek et al., comprise usability studies carried out at schools and education centres to draw conclusions regarding

Physical 3D models from LIDAR data as tactile maps for visually impaired persons 171

requirements for attractive and useful modern tactile maps and cartographic media. Another overview of tactile maps and map applications is given in Weckman (2008) including physically touchable maps, screen maps and mobile map applications for the visually impaired. The study described in the present paper combines the above-mentioned techniques to produce a 3D landscape model of a recreation area in the southern part of Finland. The first step is to derive elevation and vector data from LIDAR data and aerial images to be used for the 3D model. After an introduction of the study area and model characteristics in Sect. 2, this is described in Sect. 3. The processing for the elements being part of the 3D model and the export into a VRML file that is used as a source file for the printer, are illustrated in Sects. 4 and 5, followed by a short outline of the printing process in Sect. 6. Sect. 7 summarizes the results of a preliminary user test that has been carried out with two visually impaired persons. The paper closes with a discussion and ideas for further work in Sect. 8. The software used for the model creation is TerraScan™ on top of MicroStation® for laser data processing, elevation model creation and vectorization tasks, as well as ArcGIS® and ArcScene® for raster data processing, visualization and VRML export.

2 Model Area and Layout The model created in this study covers an area from the Finnish Geodetic Institute's (FGI) Nuuksio test environment (Sarjakoski et al. 2007). It is located in Nuuksio National Park in the City of Espoo, South Finland, and includes the Solvalla sport and recreation area, a skiing hill nearby and a small part of the lake Nuuksion Pitkäjärvi. The FGI carried out airborne laser scanner data collections for the area in spring 2006 and summer 2007 as well as an aerial image data collection in summer 2007. As a result, there are laser data sets with a point density of approx. 4.4 points/m² (2006) or 9 points/m² (2007) and true-colour orthophotos available. The size of the 3D prototype is mainly restricted by the print size of the 3D printer. The maximum dimension for a one-piece print is about 25 x 35 x 20 cm3 (DESIGNmate CX™ printer model). The area covered by the model is 700 x 950 m2 which leads to a scale of 1:3000 for the prototype. The contents of the model are influenced by the special needs of visually impaired persons. The aim was to create a tactile map for those who rely on other senses besides a limited sense of sight. Therefore, the final 3D print does not only map topographic objects to enable the


orientation and to give an impression of the area, but also makes them tactile. This aim was achieved by emphasizing buildings, roads and foot paths from the ground, using a texture for water areas, as well as utilizing strong, rich-in-contrast colours for certain objects.

3 DEM, DSM and Vector Data Creation The starting point for the creation of the 3D model was a DEM and a DSM which were both derived from the laser data. Error points including points below the ground and points resulting from noise in the air have been filtered out from the raw laser point cloud. Furthermore, the point cloud was filtered into ground and vegetation points as well as points resulting from water bodies and other above-surface objects. The DEM was extracted as a 1 m-grid file by using only the ground points while the DSM was extracted as a 1 m-grid file from the ground and vegetation points. Additionally, such objects as buildings, roads and paths were vectorized based on the laser points and the orthophotos. Especially for buildings, the detection from laser data offered some advantages compared with detection from orthophotos. They could be digitized in a semi-automatic way which resulted directly in realistic 3D building models that were well suited for visualization purposes (Fig. 1). Boundaries of water bodies were available from a topographic data-base.

Fig. 1. The representation of the 3D vector data for buildings, roads, paths and water areas on top of the DSM (colour version on CD-ROM)


4 Raster Data Processing The vector data were divided into different data layers according to the objects they represent: roads, paths, buildings and water areas. For further processing of the 3D model, raster data sets were created for all vector data layers. The different processing steps applied for each object type along with the additional changes of the original DSM are described in the following sections. 4.1 Buildings The 3D vector models for buildings were created by semi-automatic building detection tools in TerraScan™, a software for processing LIDAR data and extracting vector elements based on laser point clouds (Terrasolid 2010). This resulted in MicroStation® design file elements with shapes for walls, roof top, roof bottom, and roof sides for each building. The design file was imported into a 3D shapefile. From the detailed vector models, the roof tops were used to be converted into a raster layer (GRID). This vector-raster conversion had the advantage of being straightforward, but it also lost the roof form. The resulting building models had a single height (roof top) and were represented by flat shapes. Another approach was tested by creating TINs for the roofs first to keep the roof form, and converting those TINs into a GRID afterwards. This resulted in a correct roof structure for some buildings. However, after converting roof polygons into TINs, some of the building boundaries were represented poorly especially for adjacent buildings. Therefore, this approach was dropped for the model creation. In order to further emphasize the buildings from their surrounding, a buffer was created around them. The buffer width was 3 pixels which is equal to 1 mm in the final model. The areas of the buffered buildings were cut from the DSM and filled with ground heights from the DEM to remove for example trees next to buildings. 4.2 Roads and Paths The roads and paths were processed in a way that makes them easy to follow by tactile means. They were raised from the ground and surrounded by a corridor to cut off objects nearby in the DSM. There is a difference in symbolization between roads and paths. While paths are represented by simple linear features, roads consist of a road body and a centreline on top


of that. The design of a road including dimensions for the elements is illustrated in Fig. 2.

Fig. 2. A schematic representation of the road in the 3D model

Starting from the centrelines of roads and paths, several raster layers were derived to raise them from the ground. The use of distance functions generated a bank-like shape in the final model. Similar as for buildings, buffer areas were created around roads and paths to cut corridors from the DSM. An additional raster layer served as a mask for manipulating the model height values within the corridors. The application of a logarithmic function for calculating the cell values of the mask gave the corridor a more rounded shape compared with a linear function. Fig. 3 provides an illustration of the mask layer for corridors around traffic routes. The DSM heights within the corridors were recalculated with the help of the corridor mask. A conditional expression utilizing the DEM, DSM and the mask layer was applied to obtain a smooth transition between corridor and non-corridor areas: DSM_cor = con (isnull(COR_log10), DSM_1m, (DEM_1m * COR_log10 + DSM_1m * (1 - COR_log10)))

(4.1)

where DSM_cor is the manipulated DSM, DEM_1m the original DEM, DSM_1m the original DSM, and COR_log10 the mask for the corridors. The cell values of the mask layer can be seen in Fig. 3.


Fig. 3. The corridor masks for roads and paths. The grayscale values symbolize the factors for being multiplied with the DSM and DEM heights according to Eq. 4.1 (colour version on CD-ROM)

4.3 Trees The original DSM was extracted from the ground and vegetation points of the laser point cloud. Therefore, the trees were a part of the DSM and were represented by more or less sharp spikes in the model. These spikes were smoothed by a 3x3 mean filter to make the touch of the trees comfortable in the final 3D print. Additionally, the elevation values of the DSM were manipulated by a factor of 0.33. This smoothed the trees significantly but also preserved smaller trees and bushes (Fig. 4). Furthermore, it was still possible to generally distinguish between higher trees in forests and lower vegetation areas.

Fig. 4. A comparison of trees in the original DSM (left) and after smoothing (right)


4.4 Textures Water areas were symbolized with a 3D texture to make them distinguishable by tactile means. A shapefile was produced with lines in a zig-zag-pattern inside the lake boundaries. The pattern type was chosen based on a study on the perceptibility of different symbols for areas in tactile maps (Weckman 2008). A raster layer was created from the line shapefile that raised the texture lines from the DEM water level by 2 pixels which is equal to about 0.7 mm in the final model. 4.5 Putting it all together The previous sections described the raster data processing for the different objects which became a part of the final model (Fig. 5, left). These parts were combined into one raster file for the print file creation. Therefore, the first step was to smooth the trees in the original DSM. In the second step, the buffers were applied to the smoothed model including the areas around buildings and the corridors for roads and paths. Finally, the raster files for buildings, roads, paths and the texture were combined and merged with the smoothed DSM. The following command illustrates the process: DSM_final = merge(mosaic(BUILD, ROAD, PATH, TEXTURE), DSM_smooth)

(4.2)

Where DSM_final is the final model, BUILD, ROAD, PATH, TEXTURE are the corresponding raster layers for the above-ground objects, and DSM_smooth is the smoothed DSM including buffer areas and corridors. An illustration of the final model is shown in Fig. 5 (right).

Fig. 5. The separate elements of the 3D raster model (left) and the final combined raster model in a hill-shade representation (right) (colour version on CD-ROM)


5 Colouring and VRML Export An orthophoto was draped on the final model to carry out the 3D visualization. This resulted in a realistic representation of the area (Fig. 6, left). Regarding the special requirements of visualizations for visually impaired persons, this is not necessarily the best solution. Therefore, the original orthophoto was manipulated with image processing software to emphasize certain objects by colour. Sport fields were coloured in light green, buildings in red, roads in yellow with a black centreline, paths in orange, parking areas in white, and water bodies in blue. The edited orthophoto supports the recognition of objects for persons who can distinguish between strong and rich-in-contrast colours (Fig. 6, right).

Fig. 6. The final DSM superimposed by the original orthophoto (left) and the orthophoto with modified colours for water, roads, paths, buildings, sport fields and parking areas (right) (colour version on CD-ROM)

The final DSM superimposed by the manipulated orthophoto was then exported to a VRML file that can be read by the printer software (ZPrint™). For the current model size and a resolution of 1 m the size of the VRML world file (.wrl) was about 22 MB. The orthophoto was tiled into 12 images. Besides serving as a source file for the printing process, the VRML file can also be used for visualization purposes in VRML viewers. This may be helpful for providing a preview of the printed model. It enables the presentation without special software as VRML viewers are also available as browser plug-ins.

6 The 3D Printing Process For the present study, the 3D model was printed on a Contex DESIGNmate CX™ printer. In the printing process, a roller applies fine plaster powder over the model area for one layer at a time. On places that


become parts of the model, a water based binder is injected by print heads to glue the powder particles within one layer as well as with subjacent layers. True-colour models can be created by using coloured binders. In areas where no binder is applied the powder remains as bearing material for following layers. When one layer is finished the model area is lowered by the layer height of about 0.1 mm and the building process of the next layer starts. After finishing the prototype, the dispensable powder is removed for re-use in another printing process. Afterwards, the model is hardened and the epoxy resin is applied to make it stable and resistant (TU Berlin 2007). The above described printing process for the 3D model created in this study is outlined by the following Figs. 7a–f.

Fig. 7a-b. The printing model visualization in the printer software ZPrint™ (left) and the creation of the prototype layer-by-layer. Due to the use of coloured binders a true-colour model was generated (colour version on CD-ROM)

Fig. 7c-d. After the printing process, the dispensable powder was removed (left). The first hardening process took about 3 hours (right) (colour version on CDROM)


Fig. 7e-f. Epoxy resin was applied to the model before another drying and hardening process followed (left). The final 3D prototype (right), overview (top) and detail (bottom) (colour version on CD-ROM)

7 User Test with Visually Impaired Persons The prototype with its current appearance was evaluated by visually impaired test persons regarding its usefulness for supporting outdoor activities such as hiking tours. After an interview about the habits and experiences with navigation aids and tactile maps, the test persons were first asked to examine the 3D model freely and then, to solve some small tasks with the help of the model. The main opinions gathered in this experiments are summarized in the following section. 7.1 User Test Results In general, the model was considered as useful for getting an overview of the area, and for planning a route before the actual start. However, it was noted that it is not enough as only means to prepare a tour. Roads and paths were easy to realize and follow by tactile means, in this case with the finger tips. It was considered as an advantage that they were raised and not lowered from the surface model. Crossings of paths were identified as problem areas because it was often hard to recognize how many paths are crossing and to which direction a route continues. Large buildings were easy to be perceived while it was difficult to distinguish small buildings in forests from trees. The use of textures was generally regarded as good. A


suggestion was rather to texturize sport fields than water areas. Those should be flat to make the difference between water and land areas more obvious. The visualization of trees based on the original DSM, which corresponds to nearly a single tree representation, was partly considered as unnecessary. A texture was suggested as an alternative. Nevertheless, forest areas could be identified clearly while single trees led to wrong assumptions in some cases. The perception of terrain elevation was pointed out as advantageous because it was easy to discover slopes and thus differentiate steep and flat areas. Additionally, information about the inclination of paths could be derived from the model which is relevant for outdoor activities such as hiking. The colouring of the 3D print model was regarded as good for people with limited abilities to distinguish colours. 7.2 Possible Improvements Considering the opinions presented in Sect. 7.1, some changes might improve the usefulness of the model. This includes the texturing of sport fields and maybe other man-made areas that serve as an orientation help and thus should be recognizable in the prototype. Furthermore, crossings of paths and roads should be emphasized, possibly by rising them a bit more from the main linear object and marking continuing directions of routes. One solution to enable a better distinction between trees and small buildings is to expand the size of buildings and to lower the tree heights even more than in the current model. Additionally, a future model should include labels, in this case Braille letters, as well as point symbols to mark certain objects. The use of textures and symbols also requires the availability of a legend. Finally, a tactile north arrow or some other symbol marking the orientation of the prototype, and a scale bar supporting the estimation of distances should be added.

8 Discussion and Future Work This section discusses the results of the study and ideas for further work regarding three main points: the model creation process, the usefulness of the final prototype for visually impaired persons, and the 3D model for people with normal sight abilities. At the moment, the 3D model is completely raster-based. That means, for all objects raster data layers are created and finally combined into one raster data set. Although the raster layer creation is straightforward and may be automated in the future, it is an additional effort. Since buildings,


infrastructural objects, and other data are usually stored in some vectorbased format in a GIS, it requires a vector-raster conversion to include them into the model. This leads partly to the loss of information as it can be seen for building roof structures. Therefore, one future approach is to investigate possibilities to combine different data types for being used in a source file for 3D printing. On the other hand, raster data processing offers several advantages compared with vector data processing regarding DSM manipulation, as it is shown for example with the insertion of corridors, buffers and raised traffic routes. Corresponding possibilities for vector data processing have to be explored as well. In the present study, the visual and physical appearance of the 3D prototype is designed for visually impaired persons. Therefore, objects like roads and paths are raised to distinguish them from their surrounding and to enable their perception by tactile means. Additionally, certain objects are emphasized by the use of strong and rich-in-contrast colours instead of the original orthophoto colours. The model was evaluated by visually impaired test persons in a small user test. Their opinions and suggestions for improvements are described in Sect. 7. Compared with other tactile maps, the 3D model was found to be more attractive and motivating to be used by the test persons who stated not to like tactile maps in general. They could imagine the model being situated in an information centre of the recreation area to give a last overview of the area before a tour is started. However, in the user test it became also clear that the support for outdoor activities gained from the 3D print for visually impaired persons is limited. Therefore, it might be more effective to design such a model in a way that attracts and supports the visually impaired and persons with normal sight abilities alike. Besides improving the 3D print representation for the visually impaired, there are other considerations regarding a 3D visualization for persons with normal sight abilities. In such a case, the heightening of linear objects is not necessary and the coloured design is more flexible. While a truecolour orthophoto on top of the DSM offers a realistic impression of the area, the use of maps or other image data could serve certain purposes better. It might be also an advantage for some applications to colour only important and relevant objects whereas objects irrelevant for the application are only represented with a background colour. In addition to visualize the as-is situation with such a 3D model, the inclusion of planning data could be considered as well.


Acknowledgements This survey is a part of two research projects. The European Commissionsupported HaptiMap-project (FP7-ICT-224675) is coordinated by Lund University (www.haptimap.org). The MenoMaps-project is funded by Tekes (the Finnish Funding Agency for Technology and Innovation), and is a joint venture of the FGI and the University of Art and Design, Helsinki.

References Ahokas E, Yu X, Kaartinen J, Hyyppä J, Kaasalainen S, Matikainen L, Honkavaara E, Hyyppä H, Rönnholm P, Soininen A (2005) Quality of Laser scanning. In: Jacobsen K, Goossens R, Winkler P (eds) EARSeL Workshop 3D Remote Sensing. URL http://www.earsel.org/workshops/3D-RS/Paper/Ahokas.pdf (Last accessed: 27 April 2010) Geiger S (2007) Untersuchungen zur Struktur und Funktion taktiler kartographischer Medien und ihren Wechselwirkungen. Ph.D. thesis, Technical University Dresden Hyyppä H, Rönnholm P, Hyyppä J, Yu X, Kaartinen H (2006) Laser scanner derived digital terrain models for highway planning in forested areas. Nordic J Surv Real Estate Res 3(1):69–82 Maas HG (2005) Akquisition von 3D-GIS Daten durch Flugzeuglaserscanning. Kartogr Nachr 55(1):3–11 Rase WD (2007) Visualization of Cartographic Surfaces Using 3D Printing and Subsurface Engraving. URL http://www.bbsr.bund.de/cln_016/nn_340582/BBSR/DE/Raumbeobachtung/ Werkzeuge/Visualisierung/Veroeffentlichungen__Artikel/Veroeffentlichunge n__Downloads.html?__nnn=true (Last accessed: 27 April 2010) Rase WD (2009) Visualization of three-dimensional GIS objects using rapid prototyping technology. In: GeoViz 2009. URL http://www.geovisualisierung.net/geoviz_hamburg/papers/08_1_Rase.pdf (Last accessed: 27 April 2010) Sarjakoski T, Sarjakoski LT, Kuittinen R (2007): Establishing a test environment for ubiquitous geospatial applications. In: Proceedings of the XXIII International Cartographic Conference, Moscow, Russia, CD-ROM Soininen A, Korpela H (2007) Processing of Airborne Laser Data and Images. GIS Dev 11(10):38–40 Terrasolid (2010) TerraScan User’s Guide. URL http://www.terrasolid.fi/system/files/tscan_1.pdf (Last accessed: 27 April 2010)

Physical 3D models from LIDAR data as tactile maps for visually impaired persons 183 TU Berlin (2007) 3D Druck. URL http://www.tu-berlin.de/3dlabor/ausstattung/3d-druck/ (Last accessed: 27 April 2010) Voženílek V, Kozáková M, Štávová Z, Ludíková L, Růžičková V, Finková D (2009) 3D Printing Technology in Tactile Maps Compiling. In: Proceedings of the XXIV International Cartographic Conference, Santiago, Chile, CDROM Weckman S (2008) Maps and Geographic Information for Visually Impaired People. Special Assignment in Cartography, Helsinki University of Technology

Section 5: Globes

Blurring Boundaries Between Real and Digital/Virtual Globes – Creating virtual globes from real ones and vice versa Gede, M. and Ungvári, Z.

The Digital True-3D Globe from Willem Janszoon Blaeu Knust, C., Buchroithner, M. F. and Dolz, W.

State-of-the-art of Tactile Hyperglobes Riedl, A.

Blurring Boundaries Between Real and Digital/Virtual Globes – Creating virtual globes from real ones and vice versa

Mátyás Gede, Zsuzsanna Ungvári Department of Cartography and Geoinformatics, Eötvös Loránd University, Budapest, Hungary

Abstract The recently opened Virtual Globes Museum publishes three dimensional virtual models of old globes on the Internet. The main purpose of the museum is to preserve these artifacts of old cartographers and at the same time to make them available for anyone who wants to study their content without the risk of making any harm to them. In this project, the authors established a bi-directional passageway between the world of virtual/digital and real globes. The developed technologies enable the easy creation of digital globes from handmade originals as well as the reverse process: the (re)creation of handmade globes from digital ones. The “heart” of the system is the Virtual Globes Museum, in which the globes are stored in an appropriate digital format. The images of the globe surface are archived in Platte-Carée, while those of the polar regions are archived in azimuthal equidistant maps. This “globe database” is fed from various input channels. The sources can be photo sets of globes or scanned images of printed segments transformed into a uniform image. This transforming process – especially when dealing with photographs – involves the problem of georeferencing, for which a special programme was developed. This programme calculates the projection parameters of a globe photo using control points marked on it. Another possible source is a newly compiled globe, when the globe map is created in the format that will be stored in the Museum, i.e. in PlatteM. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_12, © Springer-Verlag Berlin Heidelberg 2012

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Carée and azimuthal equidistant projection. This means that no further projection transformation is necessary. A current research project is trying to define the major guidelines of editing a globe map of this type. The possible output channels are the various digital visualizing forms of the globes: VRML models or KML globe layers for Google Earth, and a “down-to-earth” version: handmade globes based on the material stored in the museum. This latter procedure makes it possible to produce “facsimile” versions of old globes even without any original printed material by using a photo series of the globe. This paper intends to show a total cross-sectional view of globe digitizing by presenting examples of each procedure: digital globes made from photos or prints; globes designed to be virtual ones; and facsimile reproduction of the processed globes. Keywords: virtual globes, VRML, KML, facsimile globes

1 Introduction Terrestrial and celestial globes are peculiar products of cartography in many aspects. First of all, unlike traditional maps, globes nowadays are rather ornaments than navigational aids. Their creation is much more difficult as manufacturers also have to produce the bearer sphere and its frame. Archiving these objects was a hard task until the recent times. The revolutional increase of computers’ power however, finally made it possible to digitise globes and visualize them on the computer’s screen also. And if a globe is somehow feeded into the computer, there is the opportunity to recreate a new copy of it, a facsimile globe. Several projects deal with globe digitising. Florian Hruby, Irmgard Plank and Andreas Riedl created the digital copy of Mercator’s globe using photographs and original prints (Hruby et al 2006). Andrea Adami and Francesco Guerra created Coronelli’s globe from its printed sheets (Adami & Guerra 2008). The Virtual Globes Museum is a little bit different from these projects. Its primary purpose is to form a virtual exhibition of the globes related to Hungary. At the same time it wants to serve as a digital archive of these globes. Using its background database it’s also possible to create facsimile globes.

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2 The Museum The central object of the project is the „Virtual Globes Museum”. It’s a web page with a background database. Its name can be interpreted two ways: a „virtual museum” of globes or a museum of „virtual globes”. It forms an on-line exhibition of three-dimensional globe models somehow related to Hungary. The website is trilingual: the user can choose between Hungarian, English and German. A simple search engine helps to browse among the daily growing number of globes (Fig. 1). Two different types of 3D models are stored in the museum: VRML globes, viewable either by an appropriate VRML player plug-in or by a Java applet; and KML „globe layers” for Google Earth. The background database stores the images and additional data about each globe. A few words are written about every globe’s history, technology, content and other important or interesting issues. All these data and the available portraits or other photos can be examined on the globes’ detailed data sheets.

Fig. 1. The Virtual Globes Museum web site (http://vgm.elte.hu)

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The globes’ equatorial areas are stored in Plate-Carée while the polar regions in Azimuthal Equidistant projection. The reasons of this choice are simple: the Plate-Carée is the easiest option when we have to assemble many smaller areas to a big map image as geographic quadrangles are rectangles in this projection. The azimuthal projection is used because of the VRML models as the poles have their own textures there.

3 Input possibilities If there are unmounted printed gores of a globe available (Fig. 2), the easiest option is to scan those prints and process them to create the virtual globe. This process involves the georeferencing of the gores, which requires the determination of their projection.

Fig. 2. Printed gore set

Although the gores of old globes didn’t have an exact projectional background, the Cassini projection fits adequately. Using as many control points as possible (the intersections of the geographic grid are used) method the results are good. Other projections may also be appropriate, but comparing a 30-degrees wide segment’s image in a few selected projections (Transverse Mercator and Polyconic besides Cassini) the


differences seem to be less than the unavoidable distortions due to paper deformations. If the prints include polar caps, they also have to be georeferenced. These caps were usually drawn in Azimuthal Equidistant projection. When printed gores are unavailable, a photo series has to be taken. The projection of such globe photographs are the same as the one of a photo of the Earth’s surface taken from the space. It is called Tilted Perspective Projection and it is a rather general projection with several parameters. As unfortunately it is not known by any of the popular GIS programmes by this time, it is advisable to find a way to use another projection. The easiest solution is to make the optical axis of the camera intersect the centre of the globe. In this case the projection simplifies to the Vertical Near-Side Perspective (Snyder, 1987). An example of georeferenced photo can be seen on Fig. 3.

Fig. 3. A georeferenced globe photograph

This projection has three parameters: the latitude and longitude of the projection centre and the height of the perspective point. A useful programme was developed to calculate these parameters from an

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appropriate set of control points using the Nelder–Mead Downhill Simplex Method (Nelder & Mead, 1965) to find the optimum values. (Gede, 2009) Whether we used gores or photos, the next step is assembling the pieces into one large image (Fig. 4). The georeferenced images are transformed to Plate-Carée because in this projection globe segments, polar caps and any other geographic quadrangles become rectangular areas so they can be fitted together easily.

Fig. 4. An assembled globe map in Plate-Carée

If we want to compile a virtual globe with brand new content rather than representing an old one, we should create three images: a Plate-Carée map for equatorial regions between ±50° latitudes and two polar caps in Azimuthal Equidistant. Hargitai used this solution to create the virtual globes of Moon and Mars and other planets. (Hargitai, 2009) There is an important issue in this method which must be taken in count: projecting the images to the sphere will distort their content so all the text should be placed after applying an inverse distortion which will ensure their normal appearance on the globe.

4 Output possibilities The most obvious format for a 3D object is a VRML (Virtual Reality Modeling Language) model. Although this language has a built-in sphere object, it is advisable to define a special object for globes. It is better to split the surface to more sub-surfaces because the computer graphic cards prefer more small textures than one large image.


A sphere built up of six sub-surfaces were developed for the Virtual Globes Museum. The equatorial areas are divided into four parts and each polar region is separated (Fig. 5, 6). The boundary latitudes vary due to the globe’s content. Mathematically, the best option would be to use the 45° latitudes, but most globes have a grid system with ten-degree intervals. Therefore, the usual boundary is 50°. There are globes however, with boundaries at ±70°. This solution was used for smaller globes having polar caps with a radius of 20 degrees which means that the original polar caps are the same as the ones in the VRML model.

Fig. 5. The VRML sphere built up of six surfaces

Fig. 6. A VRML virtual globe

VRML models can be viewed by an appropriate player software. Usually it is a free-downloadable browser plug-in. For those who do not want or cannot install plug-ins on their computers but have Java installed, the museum provides a VRML player Java applet. Another possibility is the using of KML language instead of VRML. KML (Keyhole Markup Language) is a format which can be interpreted by Google Earth and other virtual earth programmes (Google, 2009). These KML globe models become a new layer once they are loaded into Google Earth and therefore the content of old globes can be examined and analysed together with other contents like current political boundaries or coastlines etc. (Fig. 7)

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Fig. 7. A KML globe in Google Earth

5 Creating a facsimile globe Once a globe, even an unique, manuscript one, is digitised, it is possible to recreate it as a facsimile. It is something like „reverse engineering”, as the set of gores is produced using the processed photo series of the globe. To obtain the gores, the large Plate-Carée map of the globe is divided to usually 12 parts (30-degrees wide each) with some overlap at the edges. At the second step these segments are converted to Cassini projection. Two polar caps in Azimuthal Equidistant projection also have to be created. After scaling these images due to the mounting sphere’s diameter, they can be printed by a colour laserjet. The last step is the mounting of the gores and polar caps to the sphere. This is the hardest task as it needs some hand skill. (Fig. 8)


Fig. 8. Homemade facsimile globe

There are other possible solutions. Instead of 12 gores and two polar caps, two petal-shaped prints also can be created (Fig. 9). The projection background of these petals is the same as in the previous solution; but the gores are split at the Equator and they are mounted to the polar caps. The authors developed a little programme which produces these petals automatically from the Plate-Carée images.

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Fig. 9. Petal-shaped globe print

Another option could be the production of a plastic globe with the content of an old one. It needs however, a co-operation with globe manufacturer companies as the production of such plastic globes cannot be done without special machines.

6 Conclusions, discussion The globe digitising method described above is usable for most of the globes. There are, however, cases when some difficulties occur. Celestial globes sometimes don’t have a proper geographic grid. Blaeu, for example, had drawn only a few lines to his sky-globe: the Equator, the tropics of Cancer and Capricorn, the polar circles, and the Ecliptica. Additional lines are the edges of gores which are perpendicular to the Ecliptica. The intersections of these lines were the most important GCPs


for georeferencing. In areas where the number of those points was insufficient, some stars also were used. Sometimes the gores were improperly mounted to the globe. These faults can be mended on the virtual globe if the adjacent gores are georeferenced separately. When photographing a globe, the hardest challenge is to ensure homogenous lighting conditions for each photo. The best solution is to fix the camera, and only rotate the sphere around its centre. Some globes however, cannot be handled this way, because there is no possibility to take them out from their holder. In this case it is almost impossible to make all the photos homogenous in lightness and contrast. If we want to create a facsimile globe, the first task is to find a proper base sphere. Polystyrene spheres (usually available in hobby-art shops) are a good option for smaller globes. Before printing, the gores have to be scaled to fit the base sphere. A trial mounting of a piece of paper can help to determine how the paper behaves i.e. how much it will stretch for example. The glue shouldn’t dissolve the ink or the material of the sphere. The authors used decoupage glue. To facilitate the proper mounting, it is advisable to draw the place of the gores in advance.

References Adami A, Guerra F (2008) Coronelli’s Virtual Globe [on-line] http://www.eperimetron.org/Vol_3_4/Adami_Guerra.pdf Gede M (2009) Publishing Globes on the Internet. Acta Geodaetica et Geophysica Hungarica Vol. 44/I (2009) pp. 141-148 – Akadémiai Kiadó, Budapest Gede M (2009). The Use of the Nelder–Mead Method in Determining Projection Parameters for Globe Photographs. [poster] – EGU General Assembly, 2009. Google (2009) KML Documentation [internet] http://code.google.com/apis/kml/documentation/ (Last accessed: 20 August, 2009) Hargitai H (2009) Planetary globes and maps [internet] http://planetologia.elte.hu/globes/ (Last accessed: 20 August, 2009) Hruby F, Plank I, Riedl A (2006). Cartographic heritage as shared experience in virtual space: A digital representation of the earth globe of Gerard Mercator (1541) [on-line] http://www.e-perimetron.org/Vol_1_2/Hruby_etal/Hruby_et_al.pdf (Last accessed: 20 August, 2009

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Knust C, Dolz W (2008): Erstellung eines digitalen 3D-Globus nach der Originalvorlage von Willem Janszoon Blaeu Amsterdam um 1645. In: Kartographische Nachrichten, 59. Jg., Heft 2, pp. 77 – 83. Márton M (2008): Virtuelles Globen-Museum in Ungarn. In: Kartographische Nachrichten, 58. Jg., Heft 5, pp. 266 – 267. Márton M (ed) (2008) Virtual Globes Museum [internet] – http://vgm.elte.hu (Last accessed: 20 August, 2009) Márton M, Gede M., Zentai L (2008) Föld- (és ég-) gömbök 3D-s előállítása – Virtuális Földgömbök Múzeuma és digitális virtuális restaurálás – Geodézia és Kartográfia, 2008/1–2. pp. 36–42. Nelder JA, Mead R (1965) A simplex method for function minimization. Computer Journal, 7:308–313. Oxford Riedl A (2000) Virtuelle Globen in der Geovisualisierung. In: Wiener Schriften zur Geographie und Kartographie 13. Vienna: 158. Snyder JP (1987) Map Projections – A Working Manual. USGS Professional Paper 1395. pp. 173–176. Washington, 1987.

The Digital True-3D Globe from Willem Janszoon Blaeu

Claudia Knust1, Manfred F. Buchroithner1, Wolfram Dolz2 1

Institute for Cartography, Dresden University of Technology, Dresden, Germany 2 State Art Collections Dresden, Mathematical-Physical Salon, Zwinger Palace, Dresden, Germany

Abstract The importance of digital globes is increasing, not least because of their advantages in comparison to the analogue globes. In the project described below for the first time the seminal 3D display technology was used to generate a true-3D model of a historical globe for the renowned Globe Collection in the Mathematical-Physical Salon at the Dresden Zwinger Palace, Germany. The result is a true-3D film about this globe, which can spontaneously be perceived three-dimensionally with unaided eyes. With the help of this film the visitors are supposed to learn more about the content and the graphic design of the globe. Keywords: historical cartography, historical globes, digital globes, autostereoscopy, three-dimensionality, true-3D

1 Motivation Today digital products play an increasing role in various fields of science and life. Also for historical globes they become more and more important, because digital globes have several advantages over analogue ones, such as M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_13, © Springer-Verlag Berlin Heidelberg 2012

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the shorter updating cycles, easier portability and a much larger number of topics to be presented. Hence, digital globes have an enormous potential which certainly will be used much more in the future. A close collaboration between the Austrian National Library and the University of Vienna led to a multimedia globe museum in Vienna. Inspired by the positive experiences in Vienna, also in Dresden synergies between the Mathematical-Physical Salon (MPS) in the Dresden Zwinger Palace and the Institute for Cartography at the Dresden University of Technology were used to create a new globe exhibition. Manfred Buchroithner has had the idea to apply modern 3D display technologies to produce a true-3D globe. The conceptual bases for this project were investigated within a brief research study of the first author (Knust 2007) and subsequently implemented (Knust 2008). With the MathematicalPhysical Salon as principal actor, its Director Peter Plaßmeyer and the Chief Curator Wolfram Dolz were the supervisors of the projects as well as Prof. Buchroithner from the Institute for Cartography. Spatial View Inc. in Dresden generously provided the 3D display hardware and software necessary for the project.

2 Mathematical-Physical Salon The Mathematical-Physical Salon (MPS) in the Dresden Zwinger Palace is one of the eleven internationally renowned museums of the Staatliche Kunstsammlungen (State Art Collections) Dresden. The MPS owns important collections of historical clocks and scientific instruments, such as geodetic instruments and globes. The “Royal Cabinet of Mathematical and Physical Instruments” was founded in 1728. In 1746 the museum was given its current name Mathematical-Physical Salon (MPS Brochure 2006, www.SKD-MPS). The internationally famous globe collection contains several rare and important pieces. These include for example an Arab celestial globe from the 13th century, a terrestrial globe made of brass by Johannes Praetorius, Nuremberg, in 1568 and a very rare small pocket globe from Johann Baptist Homann which was also produced in Nuremberg around 1715. In the course of a general renovation of the building, which will last until 2012, a reorganisation of the permanent exhibition takes place. As mentioned before, in the new exhibition also a digital globe is planned. By using an autostereoscopic display, the viewer shall be able to see the globe stereoscopically on a screen without any viewing aids (“true-3D”). From the variety of historical globes the terrestrial globe by Willem and Joan


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Blaeu with a diameter of 68 cm (Amsterdam 1645/48; see Figure 1), of which two copies are owned by the museum, has been chosen for the project. Among others the following reasons led to this decision: x Digital data from the globe segments already existed at the Austrian National Library and the University of Vienna. These data was kindly provided to the Mathematical-Physical Salon for further treatment. x The terrestrial globe from Blaeu is very rich in detail due to its large scale and it is highly representative because of its map design.

Fig. 1. Terrestrial globe, Willem Janszoon and Joan Blaeu, Amsterdam, 1645/48 (Mathematical-Physical Salon, State Art collections Dresden; Photo: Juergen Karpinski)

The digital globe is supposed to supplement the historical analogue globe. Since the historical analogue globe is protected in a showcase, it cannot be touched and turned, and thus its access is limited. But, with the digital version of this globe the whole globe surface will be made available to the visitors and they will therefore receive more information about both the producer and the object itself to better understand its characteristics.

3 Digital Globes Digital globes reduce or totally overcome the disadvantages of analogue globes, such as restricted portability, scalability and interactivity. The

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creation of digital globes is not a recent development, there exist already numerous digital globes. The examples described below were produced since the nineties of the last century, either as facsimiles of a historical globe or as originals. By the classification the Austrian expert for digital globes Andreas Riedl (cf. Riedl 2000, Riedl 2004) all of these globes are so-called virtual hyperglobes. In contrast to the types tactile hyperglobe and hologlobe the virtual hyperglobe is digitally displayed in virtual space: x The Digital Behaim Globe: The oldest preserved terrestrial globe is the so-called "Potato" (German: Erdapfel) from Martin Behaim (1459 1507) from 1492. On the occasion of the 500-year anniversary of the Behaim Globe the historical original has been subjected to detailed analyses at the Institute of Photogrammetry and Remote Sensing at the Vienna University of Technology, Austria. The primary objective has been the rectification of the globe surface that has been heavily distorted over the centuries to a plane in order to generate spherical analogue facsimiles of the original. In addition, in 1993 also a digital version of Behaim’s Globe was created by Hans Klimpfinger at the Vienna University of Technology as a byproduct of the aforementioned project. This globe is considered the first known digital 3D-facsimile of a globe (Riedl 2005, Kraus 1992, www.BehaimGlobe). x The Hyperglobe from A. Riedl: In the late nineties of last century Andreas Riedl from the University of Vienna, Austria, examined in his monograph “Geovisualisation with Virtual Globes” the possibilities of digital globes in comparison to analogue globes. He also realised his own version of a hyperglobe with many different topics, e.g. climate and geotectonics (Riedl 2000, www.Hyperglobe). But he also investigated tactile hyperglobes. Today, the German Globoccess AG, Hamburg, which closely cooperates with Riedl, offers tactile hyperglobes and the authoring and presentation software for tactile hyperglobes named OmniSuite. For more information about tactile hyperglobes the reader is kindly referred to the chapter from Andreas Riedl in this book entitled State-of-the-art of tactile Hyperglobes. x The Digital Mercator Globe: This globe was also created at the Institute of Geography and Regional Research at the University of Vienna, Austria. Irmgard Plank (2005) and Wolfgang Henebichler (2005) created this digital terrestrial globe according to the original by Gerhard Mercator from 1541. Since the end of 2005, the globe is presented at the Globe Museum of the Austrian National Library (ANL) in Vienna. The digital globe is exhibited close to the historical original. It is visualised with a touch-screen and allows complex interactions. The user can, for


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example, fade in and out several thematic layers and also drape these layers over the historical globe image. x The Digital Karl-Theodor Globe: The terrestrial globe produced by Didier Robert de Vaugondy in 1751 was once owned by Karl-Theodor, Elector of Bavaria and the Palatinate (1724 – 1799) and is now located in University Library of the University of Heidelberg, Germany. In this case the objective of the investigations was also the restoration of the globe. The project was carried out at the Interdisciplinary Center for Scientific Computing of the University of Heidelberg. In its University Library there existed original copperplate engravings of the globe image. High-resolution scans of these pictures were made which could subsequently be processed digitally. Thus, the digital globe was produced as a byproduct of the restoration of the original (Jäger et al. 2004, www.KarlTheodorGlobe). x The Virtual Globe Museum: The Virtual Globe Museum (VGM) is a project of the Hungarian National Library and the Department of Cartography and Geoinformatics of the Eötvös Loránd University in Budapest. There are currently 45 digital globes implemented. Among others there is a 68 cm large globe pair by Willem Janszoon Blaeu from 1630 (celestial globe) and 1645/48 (terrestrial globe). In addition to the interactive operability there is information available for each globe and its producer (Márton 2008, www.VirtualGlobeMuseum). x The Digital Globes according to the world views of Strabo and Ptolemy: These globes generated by Gulya Pápay, University of Rostock, Germany, are a special case, because such historical globes never existed. They are just reconstructed globes according to the descriptions of Strabo (around 7 BC) and the writings of Ptolemy (approx. 90 – approx. 170 AD). Both globes can be interactively moved via a bar. On the "Ptolemaic" globe the labelling, the graticule and/or the outlines of the land masses according to the current knowledge can be displayed. In addition, there exists a pop-up with explanatory text for each globe (www.StraboPtolemy, Pápay 2006).

4 Willem Janszoon Blaeu Blaeu was born as Willem Janszoon (lat.: Janssonius) in Alkmaar, Netherlands, in 1571. At the age of 23 Blaeu went to Tycho Brahe in Denmark to study at the Uraniborg Observatory on the Island of Hven. Since 1598 Blaeu has worked as a publisher of maps and globes in Amsterdam. He was the most famous cartographer and globe maker of the

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17th century. Due to the similarity of his name Willem Janszoon with his strongest competitor Johannes Janssonius he chose his surname Blaeu in 1621(Allmayer-Beck 1997, Dolz 1994, Krogt 1993). Blaeu produced five different globe-pair groups. They range from a diameter of 10 cm via 13.5 cm, 23 cm, 34 cm up to a diameter of 68 cm. The Mathematical-Physical Salon owns a first edition of the large 68-cm celestial globe from 1616, two large 68-cm globe pairs and a 23-cm terrestrial globe from 1621. With the 68-cm globes, he gained a decisive victory over the products of the competing aforementioned HondiusJanssonius publishing company. Another success was the acquisition of 37 printing plates of the Mercator Atlas in 1629. In 1633 Blaeu even was appointed chief cartographer of the Dutch East India Company. After his death in 1638 his sons Joan and Cornelis Blaeu continued the business. Among the most important cartographic products of the publishing company is the "Atlas Maior" which was published in several languages since 1660 (Allmayer-Beck 1997, Dolz 1994, Krogt 1993).

5 Creation of the Digital Globe

5.1 Data Raw data for the creation of the globe image have been 40 digitised and rectified black-and-white photographs of a large historical terrestrial Blaeu Globe made available to the MPS for further treatment by the Globe Museum of the Austrian National Library (Österreichische Nationalbibliothek) in Vienna. The northern and the southern hemisphere both consist of twenty pictures, eighteen half zones and two images of the polar calottes. The pictures of the polar calottes cover the area above 70° North, the half zones each cover an area from 0° to 70° latitude and 20° longitude. There are two images for each pole needed to be able to eliminate the occluding meridian ring. In addition to the data from the Austrian National Library there exist digital colour photographs of one of the terrestrial Blaeu Globes owned by the MPS. These were mainly used to complement defects of the digital globe image processed by the 40 digital images mentioned above. Further, they were applied to define the colours for the globe image (cf. next section).


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5.2 Data preparation First, an intensive treatment of the globe gores was necessary because the images partly differed significantly in brightness and contrast. This radiometric revision was performed by means of Adobe Systems’ Photoshop. Subsequently, the globe stripes were coloured according to the historical original (cf. Knust 2007). As “master copies” served the Blaeu Globes of the MPS and other works of the Blaeus such as the “Atlas Maior” from Joan Blaeu. Figure 2 shows a part of Africa at different processing stages. The left image shows the original data, the figure in the middle shows the image after radiometric revision, and the right picture shows the final colouring.

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Fig. 2. Steps of the revision of one globe strip: original (left), result of the radiometric revision (centre) and result of the colouring (right) (colour version on CD-ROM)

The coloured images were rectified and then assembled to a single map image, equirectangular map (German: quadratische Plattkarte; cf. Knust 2007). The processing was carried out using Leica Geosystems’ ERDAS Imagine. This mosaic map (see Figure 3) could then be easily used without any further treatment as texture for the globe in the 3ds Max 3D animation.

Fig. 3. Entire globe image after the treatment (colour version on CD-ROM)

5.3 Visualisation The digital globe is supposed to be visualised in the museum on an autostereoscopic display. This means that the visitors can perceive the globe spontaneously in a three-dimensional way without any additional viewing means like polarisation- or anaglyph glasses. Autostereoscopic displays can be divided into softcopies and hardcopies. Softcopies are known as digital displays, and accordingly hardcopies are analogue (Buchroithner 2001/a and 2001/b). Depending on whether they are digital or analogue, autostereoscopic displays are characterised by different advantages and disadvantages, just to mention portability, independence of lighting conditions, possibility of animations and the dependence on electrical energy (Buchroithner 2007). Another classification of autostereoscopic displays is based on the number of potential viewers. The so called single-user displays only allow for one viewer at a time, with multi-user displays several viewers can


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perceive the three-dimensional impression simultaneously. Thus, a multiuser-display is suitable for the digital Blaeu Globe. A single-user display would be a good choice for an interactive application of the globe. For the generation and the visualisation of the digital globe the Dresden Spatial View Inc. provided the Institute for Cartography both a 24”-multi-user display and the required software and hardware for the generation of the film scenes. For “artificial” autostereoscopic viewing at least two images of an object are necessary which represent it from different viewing angles. Each eye perceives one of these images, the human brain merges them and creates the spatial impression. The multi-user display used for this project works with the barrier stripes technique for the visualisation of stereoscopic images. They consist of at least two up to nine half images which are interlaced strip by strip in an alternating way and visualised on the multi-user displays with the Power Player of Spatial View Inc. In front of the display screen a strip mask, the so-called parallax barrier, is mounted as a visual barrier. The strip mask consists of transparent and opaque stripes. They hide, depending on the viewing angle, stripes of the stereoscopic image and leave others visible for the viewer’s eyes. Thus, each eye only sees the information allotted to him (Okoshi 1976, Spatial View 2008). Figure 4 illustrates the principle of barrier stripes technique.

Fig. 4. Principle of the barrier stripes technique reduced to two stereomates (based upon Knust 2007, p. 35)

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5.4 Content For the presentation of the film in the permanent exhibition of the museum two modi have been generated: an introduction and the film per se. The introduction, a stand-by-mode, will be shown as an endless loop serving as an eye-catcher. This also allows the visitor to get used to the true-3D impression before starting the film proper, for example by pressing a key. Content of this one-minute loop is the earth rotating in the universe. It is textured with a recent landcover map as well as the historical globe image, which are morphing alternately from one image to the other. The true-3D film consists of four sections, which contain only selfproduced animations and images. First of all, information about the producer and the general characteristics of the globe is given. The following two sections visualise two historical round-the-world expeditions from the 16th and 17th century and explain several elements of the globe while passing them. The reason for the creation of these two sections is that travelogues of expeditions have been of great importance for the globe makers, because they frequently contained information about then new geographical knowledge. Thus, as representatives for the many

Fig. 5. Screenshots of the section about the round-the-world expedition of Ferdinand Magellan (1519 – 1522) (colour version on CD-ROM)


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expeditions the film will show two of them more in detail, especially with regard to the influence on the content of the map image. One of these expeditions is the round-the-world expedition of the Portuguese seafarer and explorer Ferdinand Magellan (1519 - 1522). The other one is the round-the-world expedition of the two Dutchmen Jacob Le Maire and Willem Cornelisz Schouten (1615 - 1617). Figure 5 shows several film clips of the section about Ferdinand Magellan's round-the-worldexpedition. The last section gives information about the accuracy of the historical map image. Therefore, a raster image of the land masses according to the current knowledge is put on top of the historical globe image. Then characteristics of the map image are highlighted by temporarily flashing red borders. During the whole film a speaker gives explanations to the elements shown. 5.5 Animation and Audio The content of the film was created with the 3ds Max animation software from Autodesk. For the subsequent rendering of the stereo images the MaxPlug-in provided by Spatial View Inc. was used. Due to this plug-in, it was only necessary to position just one camera in the Max scene. After

Fig. 6. Arrangement of the stereomates of one stereo image

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setting all parameters, the plug-in automatically positioned the other cameras required for the stereo image rendering. The depth effect of the entire scene can be adjusted by modifying the three auxiliary planes in the Max scene. Two of them, the near and the far plane, limit the 3D scene in the near and far range. The third plane, the projection plane, represents the display level. Depending on where an object of the Max scene is located in relation to this projection plane, it finallally appears in front of, in or behind the display plane of the autostereoscopic display. Objects that are located between near plane and projection plane appear in front of the display. Objects that are located between the projection plane and the far plane seem to be behind the display plane. The stereo images for the film were rendered with a resolution of 1920 x 1350 pixels. Each stereo image contains all five sub-images in an arrangement of two images in horizontal and two and a half images in vertical direction (see Figure 6). After the rendering of all stereo images of one section, they were assembled with the free software VirtualDub to a “sub-movie”. Thus, five sub-movies were created. In addition, several stereo images were rendered for the cross-fading. The adding of spoken text definitively improves the quality of the film. The shown elements are orally explained, and thus it is easier to understand the contents of the film. Therefore, it is not necessary to insert explanatory descriptions on the screen, which would reduce the display area for the globe visualisation. It was of great importance to ensure that the film is understandable for laymen. Thus, the use of technical terms was limited and the sentences kept short and concise in order not overwhelm the audience with unnecessary information. Presently the film is only dubbed with German spoken text, but it is envisaged to add further languages for foreign visitors. In addition, background music and other sounds shall be implemented. With the video editing software Adobe Premiere Pro the five “submovies” were assembled with cross-fading images and audio files to the final, nearly nine minutes long film. For the visualisation of the film on the autostereoscopic display of Spatial View a special player software, the SVI PowerPlayer, is needed. With this player the videos and images created with 3ds MAX are interlaced and visualised according to the display requirements.

6 Conclusion The digital Blaeu Globe represents a first attempt to supplement the analogue by a digital form of the globe to convey more information about this object to the visitor. Since the historical analogue globe is protected in


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a showcase, it cannot be touched and turned, and thus its access is limited. With the help of the true-3D digital globe the whole globe surface can be made available to the visitor. In addition, the conveyance of background information is possible. In the future more historical globes owned by the museum may be digitised and presented as a film or even as interactive autostereoscopic applications. The digital Blaeu Globe is considered a first step of combining traditional exhibition forms with modern true-3D visualisation technique in order to optimise the flow of information.

References

1 Literature Allmayer-Beck P E (ed) (1997) Modelle der Welt – Erd- und Himmelsgloben. Christian Brandstätter Verlag, Vienna Bollmann J and Koch W G (eds) (2001) Lexikon der Kartographie und Geomatik, Vol. 1, A to Karti. Spektrum Akademischer Verlag, Heidelberg / Berlin Buchroithner M F (2001/a) 3D-Kartographie (encyclopedia catchword). In: (Bollmann and Koch, 2001): 169 Buchroithner M F (2001/b) 3D-Visualisierung (encyclopedia catchword). In: (Bollmann and Koch, 2001): 170 Buchroithner M F (2007) Echtdreidimensionalität in der Kartographie: Gestern, heute und morgen. In: Kartographische Nachrichten, 05/57: 239-248, Deutsche Gesellschaft für Kartographie e.V., Kirschbaum Verlag, Bonn Dolz W (1994) Erd- und Himmelsgloben – Collection Catalogue. Staatlicher Mathematisch-Physikalischer Salon, Dresden Henebichler W (2005) Digitale kartographische Ausdrucksformen im Schulunterricht – Technische Umsetzung eines Hyperglobus mittels Shockwave 3D. Diploma Thesis, University of Vienna, Institute of Geography and Regional Research Jäger W, Krömker S, Wolgast E (eds) (2004) Der Heidelberger Karl-TheodorGlobus von 1751 bis 2000 – Vergangenes mit gegenwärtigen Methoden für die Zukunft bewahren. Writings of the Mathematics-Natural Science Class of the Heidelberg Academy of Sciences and Humanities 14, Springer Verlag, Berlin / Heidelberg / New York Knust C (2007) Konzeption eines digitalen historischen Globus für den Mathematisch-Physikalischen Salon zur Visualisierung an einem 3D-Display. Pre-Thesis (unpublished), Dresden University of Technology, Institute for Cartography Knust C (2008) Erstellung eines digitalen Globus für ein autostereoskopisches Display basierend auf dem historischen Original eines Erdglobus von Willem Janszoon Blaeu. Diploma Thesis (unpublished), Dresden University of Technology, Institute for Cartography

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Kraus K (1992) Photogrammetrie und Fernerkundung angewandt auf den BehaimGlobus. In: Bott G (ed) Focus Behaim Globus. Ausstellungskatalog des Germanischen Nationalmuseums, Verlag des Germanischen Nationalmuseums, Nürnberg: 301-308 Krogt P Van der (1993) Globi Neerlandici – The Production of Globes in the Low Countries. English translation: Elizabeth Dowerman, HES Publishers, Utrecht Márton M (2008) Virtuelles Globen-Museum in Ungarn. In: Kartographische Nachrichten, 05/58: 266-267, Deutsche Gesellschaft für Kartographie e.V., Kirschbaum Verlag, Bonn MPS Brochure (2006) Information brochure of the Mathematical Physical Salon. Text: P. Plaßmeyer, State Art Collections Dresden Okoshi T (1976) Three-Dimensional Imaging Techniques. Academic Press, New York Pápay G (2006) Zur Frühgeschichte der Erdgloben. In: Zentai L, Györffy J, Török Zs (eds): Térkép-Tudomány, Map-Science, Karte-Wissenschaft: Festschrift to the 65th birthday of Prof. István Klinghammer. ELTE Térképtudományi és Geoinformatikai Tanszék, (= Studia Cartologica, 13): 323-333, Budapest. URL: http://lazarus.elte.hu/hun/digkonyv/sc/sc13.htm. Accessed 26 July 2010 Plank I (2005) Problematik der Globenbild-Erstellung für virtuelle Globen – Gezeigt anhand der Faksimilierung eines historischen Globus und der Umsetzung von Globenbildern für einen virtuellen Globus zu Unterrichtszwecken. Diploma Thesis, University of Vienna, Institute of Geography and Regional Research Riedl A (2000) Virtuelle Globen in der Geovisualisierung. Wiener Schriften zur Geographie und Kartographie, 13, 158 p, University of Vienna, Institute of Geography and Regional Research Riedl A (2004) Entwicklung und aktueller Stand virtueller Globen. In: Kainz W, Kriz K and Riedl A (eds): Aspekte der Kartographie im Wandel der Zeit. University of Vienna, Institute for Geography and Regional Research. (= Wiener Schriften zur Geographie und Kartographie, Vol. 16): 256 – 263 Riedl A (2005) MUGL – Multimediales Globenmuseum. Mitteilungen der Österreichischen Geographischen Gesellschaft, Vol. 147: 265-282, Vienna Spatial View GmbH (2008) Information material about products of Spatial View GmbH, Dresden

2 Links (www.SKD-MPS): State Art Collections Dresden, Mathematical-Physical Salon (German: Staatliche Kunstsammlungen Dresden, MathematischPhysikalischer Salon): http://www.skdmuseum.de/de/museen-institutionen/semperbau-mitzwinger/mathematisch-physikalischer-salon/index.html (Last accessed: 26 July 2010) (www.SpatialView): Spatial View Inc.: http://www.spatialview.com (Last accessed: 26 July 2010)


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3 Links Digital Globes (www.BehaimGlobe): The Digital Behaim Globe: www.ipf.tuwien.ac.at/teaching/vrml/behaim/24/behaim.html (Last accessed: 26 July 2010) (www.Hyperglobe): The Hyperglobe from Andreas Riedl: www.hyperglobe.info (Last accessed: 26 July 2010) (www.KarlTheodorGlobe): The Digital Karl-Theodor-Globe: www.iwr.uni-heidelberg.de/groups/ngg/Globus1751 (Last accessed: 26 July 2010) (www.StraboPtolemy): The Digital Globes according to the world views of Strabo and Ptolemy: http://www.phf.uni-rostock.de/imd/forschung/globen/globen.html (Last accessed: 26 July 2010) (www.VirtualGlobeMuseum): The Virtual Globe Museum: http://terkeptar.elte.hu/vgm/main.php?lang=en (Last accessed: 26 July 2010)

State-of-the-art of Tactile Hyperglobes

Andreas Riedl Department of Geography and Regional Research, University of Vienna, Vienna, Austria

Abstract This article focuses on the successor of virtual globes namely tactile hyperglobes. These tactile hyperglobes allow – as opposed to the two dimensional representation of Geo-Browsers (e.g. Google Earth, Virtual Earth ,…) – the earth’s presentation in her natural and three-dimensional appearance. This makes it easier for the user to link the information on the globe to the reality that the globe is representing. The Department of Geography and Regional Research of the University of Vienna invested in the beginning of 2005 in a tactile hyperglobe. Therefore this department is the first European research facility which focused research activities on the visualization of global topics under the use of spherical displays. On the one hand this paper will give insight in advantages and disadvantages of different types of tactile hyperglobes from a technical perspective and on the other hand introduces the functionality of OmniSuite, software dedicated to tactile hyperglobes. Keywords: 3d-visualization, digital globes, geo-multimedia, globes, hyperglobes, spherical displays


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1 The terminology of digital globes The following definition applies in the same way to both traditional analogue globes and digital globes: "A globe is a scale-bound, structured model of a celestial body (respectively firmament) presented in its undistorted three-dimensional wholeness" (Riedl 2000) In general globes can be distinguished regarding their implementation by three parameters (Riedl 2006): x The nature of the cartographic image (analogue, digital), x The character of the globe body (physical, real) and x The kind of representation space (real, virtual). Besides the well-known analogue physical globe the following categories of digital globes can be identified (Riedl 2000): x Virtual hyperglobes: Visualization of the digital image on a virtual globe body in virtual space. x Tactile hyperglobes (material hyperglobes): Visualization of the digital image on a physical (touch-sensitive) globe body in real space. x Hologlobes: Visualization of the digital image on a virtual globe body in real space.

Fig. 1: Categories of digital globes. (slightly modified, Riedl 2006)


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A three-dimensional model is a basic requirement for digital globes. But the emphasis is on “its undistorted three-dimensional wholeness”. Therefore, today’s overused term “digital globe” for applications like Google Earth or Virtual Earth 3D is valid only to a certain extent. More precisely, these “Geo-Browsers” serve as a kind of interface to large-scale geo-data or maps. There is a stronger emphasis on detailed information of earth’s surface (or other celestial bodies) and less on the globe as a whole with its global in-terdependencies. Geo-Browsers produce maps in the broadest sense of the term, mostly in some perspective view. Therefore a geo-browser is a geo-multimedia application, where a digital globe (virtual hyperglobe) is one of his features. For in depth discussions on the term of (digital) globe refer to Hruby et al. (2009), Riedl (2000, 2008), Scheidl (2009).

Fig. 2: Tactile Hyperglobe (Technorama, Winterthur, Switzerland - installed by Globoccess 2008).

2 Variants of tactile Hyperlobes The era of tactile hyperglobes started in 1992 with the “GeoSphere Globe” in Brazils’ space research centre. This was the first globe (2m in diameter), which offered the possibility to project global images onto a translucent

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sphere. Contrary to today’s projection systems the projectors were not made for permanent operation. Therefore a translucent satellite image was superimposed on the spheres surface in order to show an image when the projection system was turned off. Subsequently different technical approaches have been tested concerning tactile hyperglobes. Today one can speak of small-scale industrial production. In general tactile hyperglobes have in common that the display serves as globe-body as well as visual display unit. The following techniques for projecting the image onto the globe can be differentiated (Riedl 2008): 2.1 Outside-projection: Systems with an outside-projection use a perspective azimuthal projection for mapping the image on the sphere. Typically the system consists of four beamers positioned along the sphere’s equator. Sometimes a fifth or sixth projector is used for mapping the pole regions.s

Fig. 3: Outside-projection system (top-view).

2.2 Inside-projection: Systems based on an inside-projection use a special azimuthal projection for projecting a world map through a hole at the sphere’s bottom via


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optical system onto an acrylic glass ball. The optical system is based either on special lenses (fisheye) or on a convex mirror. Fisheye-based hyperglobes are limited to a single beamer, whereas mirror-based systems are able to use two beamers simultaneously (doubling the resolution).

Fig. 4: Inside-projection systems, fisheye-based (left) and mirror based (right).

2.3 Direct-projection: We speak of direct-projection when the spherical display is both, projector and screen. They are currently not available. Flexible OLED-displays may pave the way, but there are still five to ten years to go. Spherical displays with direct-projection would have the best image quality: no pixel distortion, no blind spots on the globe, no shadowing of the projection beam, high resolution. Furthermore the globe-body can be either “solid” or “inflatable”. Whereas inflatable displays are primarily intended for mobile applications and solid displays for permanent installations. Actually there are about 10 companies, which offer spherical displays resp. tactile hyperglobes.

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Tab. 1: Pros (+) and cons (-) of projection techniques (modified Riedl, 2008) OutsideProjection Resolution Image Quality Installation/Deinstallation Ambient light insensitiveness Space requirment Hardware requirement Blind Spot Shadowing of projection beam

+++ +++ ++ +++ -

Inside ProjectionFisheye + + ++ + +++ + ++ +++

Inside Projection - Mirror ++ ++ + + +++ + + +++

3 Authoring and presenting global Stories The biggest advantage of a globe in general is that it is distortion free and shows spatial relationships found in the real world. There simply does not exist another cartographic product that comes as close to a globe from this perspective. Contrary to virtual hyperglobes, in the case of tactile hyperglobes one is in front of a real (scale-downed) 3d-model of the earth (or any other celestial body). Seeing a tactile hyperglobe in action is fascinating. Like being an astronaut and looking from outer space on earth, or in other words: “Oh, my God! Look at that picture over there! Here’s the Earth coming up. Wow, is that pretty!" (Frank Borman, commander Apollo 8) In order to create gripping content for tactile hyperglobes some tasks have to be done. On the one hand, data needs to be projected onto a 3Ddisplay geometrically correct. On the other hand, the results of this projecting process have to be controllable and accessible in a user-friendly way. The projection problem may be considered as a cartographic basic task: The base maps for global topics are typically in an equirectangular projection (plate carrée). This global map gets translated into a special azimuthal projection (fig. 5). This azimuthal projection includes the path of rays and recurring reflections inside the globe. Here ends the routine, because the rendering must be done in real-time to give functional-


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associative correct feedback to the users in reference to their manipulations via direct manipulation interface.

Fig. 5: Projecting process for a tactile hyperglobe (single beamer)

The Hyperglobe-Research-Group at the Department of Geography and Regional Research (University of Vienna, Austria) is developing an Authoring and Presentation Software dedicated to tactile Hyperglobes called OmniSuite. We make use of C++ and the open source ObjectOriented Graphics Rendering Engine (OGRE) that offers numerous relevant features, e.g. the combination of different layers or the support of different graphics file formats (Hruby et. al. 2008). For in depth information on programming and software engineering related to OmniSuite see Kristen (forthcoming 2009).

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OmniSuite’s 3D-engine is responsible for projecting and rendering the content in real-time according to the user interactions and used globesystem (see chapter 2). One focal point of the software was the development of a (globe-)platform independent 3D-engine. Therefore a set of needed parameters had to be identified and implemented in different settings, some of the adjustable parameters are: x Display-settings (touch screen, globe-projector(s), external info-screen) x Initial-image: default story, sweet spot x Projection settings (fig 6): scaling, offset, horizontal adjustment … x Image-quality/performance tuning: mesh resolution, cube map resolution, antialiasing … x Debug info: performance status, log files

Fig. 6: Projection settings

Another focal point of our research group is creating content for the globe. OmniSuite’s StoryEditor (authoring module) provides tools for content creation according to a storyboard. The content has to be specific


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to the user’s needs. Therefore we take in consideration feedback from visitors of our tactile hyperglobe (1,5m in diameter). As a result the presentation of themes is usually made in a dynamic way via animations and in combination with short stories like explanations. Those “stories” makes it easier for users to understand causal interdependencies and processes. The story library of experienceable themes includes amongst others: x Effects of earth-sun-relationship and earth rotation (seasons, course of the day, time-zones) x Surface of the earth (topography, satellite imagery) x Geology themes like continental drift (from 600 Mio years in the past to 100 Mio in the future) x Climate and oceanography (real time weather, hurricanes, snow line in the course of the year) x Ecology (climate change, El Niño, air pollution) x Traffic (shipping traffic, air traffic) x Economy (fishing areas, crop yield, economic power) x Alliances, pacts, military power x Extraterrestrial themes (sun, planets, moons, constellations) x Historical globes x Advertisement, promotion, public relations x Digital art and entertainment

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Fig. 7: OmniSuite’s controller interface (master-mode, dark-skin design)

Furthermore OmniSuite gives the story author the possibility to implement interactive functionalities that allows manipulation by the user regarding the three interaction categories (orientation and navigation, altering the visual appearance, information retrieval). These include: x Assigning an image or image sequences (e.g. global maps) to a certain layer (default-layer, legend-layer …) x Specifying a layers extension (default-layer across the whole globe, legend on a section) x Defining an animation (duration, speed, loop, forward/backward) x Referencing audio tracks x Switching layers on/off x Defining bookmarks x Controlling the globe’s rotation Typically user interactions with the globe are performed via graphical us-er interface (GUI) on a touch screen. Implementing a GUI can be done in many different ways. The simplest one is by using OmniSuite’s interface templates and varying it with skins (fig. 7). More experienced authors can alter the templates or design complete new GUIs based on html/css or flash.


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4 Conclusion The field of applications of tactile hyperglobes ranges from representation purposes, public relation activities, installations in museums, digital art exhibitions up to edutainment and didactics. One of the intriguing installations of a tactile hyperglobe can be seen at the Technorama in Winterthur (Science Center, Switzerland). With tactile hyperglobes users are able to “see and feel” the globe in reality like an astronaut. Hence a close emotional relationship with matchless quality of experience evolves in a natural way. This matchless quality of experience is proved by user feedback. Therefore after 500 years of globe history (Erdapfel, M. Behaim, 1492, oldest preserved globe), respectively 2200 years (Krates von Mallos, 200 B.C., only written evidence) globes will have a new prosperous era.

References Beck A (2006) Google Earth and World Wind: remote sensing for the masses. In: Antiquity 80, 308 – http://antiquity.ac.uk/ProjGall/beck/ Blower J, Gemmell A, Haines K, Kirsch P, Cunningham N, Fleming A. Lowry R (2007) Sharing and visualizing environmental data using Virtual Globes. In: Proc. of the UK e-Science Meeting 2007, pp 102–109 Hruby F, Kristen J, Riedl A (2008) Global Stories on Tactile Hyperglobes – visualizing Global Change Research for Global Change Actors. In: Proceedings, Digital Earth Summit on Geoinformatics: Tools for Global Change Research, Potsdam, Germany Hruby F, Miranda R, Riedl A (2009) Bad Globes & Better Globes – multilingual categorization of cartographic concepts exemplified by “map” and “globe” in English, German and Spanish. Proceedings, 24. ICA Cartographic Conference, 2009. Santiago, Chile Kretschmer I (2000) Globenforschung in Österreich. In: Riedl A. (2000), pp 141– 155 Kristen J (2009) 3D Grafikprogrammierung interaktiver kartographischer Echtzeit-Anwendungen – am Beispiel eines taktilen Hyperglobus. Wien, Univ. Wien, Dipl.Arb.(forthcomming) Möller M (2008) Geobrowser – Katalysatoren für Geoinformation im Unterricht. In: Jekel T., Koller A., Donert K. (Hrsg.), Learning with Geoinformation III – Lernen mit Geoinformation III, Heidelberg, pp 159–170 Riedl A (1999) Virtual Globes. A New Era for Globes? In: Proc., 19. ICA Cartogr. Conf., Ottawa, 1999, pp 649–656 Riedl A (2000) Virtuelle Globen in der Geovisualisierung. Untersuchungen zum Einsatz von Multimediatechniken in der Geokommunikation (mit einem

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Nachwort „Globenforschung in Österreich“ v. Kretschmer I.). (= Wiener Schriften z. Geogr. u. Kartogr., 13) Riedl A (2005) MUGL - Multimediales Globenmuseum. In: Mitteilungen der Österreichischen Geographischen Gesellschaft, Bd. 147. Wien, 2005. pp 265 282 Riedl A (2006) Digital Globes. In: Cartwright W., Peterson M.P., Gartner G. (Hrsg.), Multimedia Cartography, Second Ed., Springer Verlag, Berlin – Heidelberg, pp 255–266 Riedl A (2008) Entwicklung und Perspektiven von Taktilen Hypergloben. In: Mitteilungen der Österreichischen Geographischen Gesellschaft, Bd. 150. Wien, 2008, pp 340-356 Riedl A (2009) Taktile Hypergloben – die nächste Stufe in der Globenevolution. In: Kriz K., Kainz W., Riedl A. (Hrsg.): Geokommunikation im Umfeld der Geographie. Wien, Institut für Geographie der Universität Wien, 2009 (=Wiener Schriften zur Geographie und Kartographie, Band 19) Scheidl W (2009) Virtuelle Globen im Unterricht – Multiperspektivische Untersuchung des didaktischen Potenzials von Google Earth und NASA World Wind im Geographieunterricht Allgemeinbildender Höherer Schulen, Master Thesis, Donau Universität Krems Schleicher Y (2008) Geobrowser-Didaktik – ein Beitrag zur aktiven Erweiterung des topographischen Wissens. In: Jekel T., Koller A., Donert K. (Hrsg.), Learning with Geoinformation III – Lernen mit Geoinformation III, Wichmann, Heidelberg, pp 60–69. Schratt A, Riedl A (2005) The Potential of Three-Dimensional Display Technologies for the Visualization of Geo-Virtual Environments. In: Proceedings, 22. ICA Cartographic Conference, 2005. A Coruña, Spain

Section 6: True 3D in Geophysics and Geology

Explanation of the BGS Subsurface Viewer Armstrong, R. W.

Three-Dimensional Visualisation of the Tectonic movement over Mexico by means of the Global Positioning System (GPS) measurements Márquez Azúa, B. , Ledesma Tello, I. L., Sánchez, J. G. and Ascencio Escamilla, M. G.

Explanation of the BGS Subsurface Viewer

Robert W. Armstrong NERC, British Geological Survey, Nottingham, United Kingdom

Abstract The BGS Subsurface Viewer is a standalone software package that allows viewing of pre-defined and incorporated 3D geological models that can also contain many other varying properties of the geological structure. This report summarizes the key technological aspects of the software and gives an outline of the flexibility of, and methodologies involved in, its operation. Keywords: Subsurface Viewer, GSI3D, Visualization, Geology

1 Introduction The Subsurface Viewer is a package developed by INSIGHT Geologische Softwaresysteme GmbH for the visualization and analysis of digital geoscientific spatial models. The viewer has been developed following the popularity of INSIGHT’s Geological Surveying and Investigation in 3D (GSI3D) software tool that is in use extensively inside the British Geological Survey (BGS) for the construction of systematic near surface models (Kessler and Mathers 2004; Kessler et al. 2005; Kessler et al. 2009). These notes describe and display the use of the interface windows to the software.


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A Geological Model is embedded within the Viewer as a means of publication and distribution to the wider world. In this way the constructed model can be examined and analysed to produce: x models displaying the geology or other pre-selected applied themes (e.g. hydrogeological properties) x geological maps (at surface and uncovered) x user defined synthetic borehole logs x user defined horizontal slices and vertical sections x visualization of the geometry of single and combined units The model supplied with the Subsurface Viewer is encrypted and cannot be altered, nor can users add additional data as the viewer is a standalone package. The model and the necessary Java software and extensions are all included in the package. The model described herein (West Thurrock) is freely downloadable from the BGS website at: http://www.bgs.ac.uk/science/thamesgateway/3dModels.html

2 Subsurface Viewer Interface The Subsurface Viewer contains up to four windows for the visualisation of the model as shown in Fig. 1. Three windows open immediately within the software. These are the Map (plan view) shown alongside the 3D view, with the Synthetic horizontal section window underneath. A fourth window, the Synthetic borehole log viewer is activated separately and positioned by the user. The model is displayed in the Map and the 3D window with its default settings. The horizontal Section window is empty until a section line is drawn. The Synthetic borehole log window opens by clicking on the borehole icon in the top left of the header bar. Fig. 1. Windows available in the Subsurface Viewer (see appendix)

In all display windows, the Explorer tab shows the table of contents and the Legend tab (not in Borehole log) reveals the colour key to the geological units in each of the three main windows. The layers that make up the model can be viewed by double clicking the left mouse button on the ‘View’ icon, with clicks on the ‘plus’ and ‘minus’ icons expanding or contracting the displayed menus. Individual layers or units of interest can be turned on and off as intimated by Fig. 2. ‘X’ and ‘Y’ coordinates can be viewed in the bottom


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left of the interface when the cursor is placed in the Map (Coordinates will only appear when all maps in both the Map and 3D windows have been turned off). Additionally, a Z (depth in metres) value can be obtained when a synthetic cross-section has been drawn and the cursor is placed in the Synthetic section window. All the windows and tab boxes can be resized.

Fig. 2. Example Explorer and Legend tab

This paper will firstly describe some of the differing attribute themes available within the data, before continuing by outlining the functionality available within the individual windows.

3 Attribute themes

Fig. 3. Attribute theme selection box

The NAME menu shown at Fig. 3. is located at the top left corner of the software is from where the various attribute themes are selected and indicates which one is being displayed. Toggling the up and down arrows and clicking once on the attribute will define a new attribute and show it in the Map, 3D and Synthetic section windows. The traditional, default appearance of the horizontal section (Stratigraphy-see Fig. 1.) is coloured by the standard BGS geological

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colours and shows a large area of chalk with a synclinal structure to the left primarily containing the Thanet Sand Formation, Harwich Formation and the London Clay.

Fig. 4. Lithology of rocks (colour version on CD-ROM)

The same geological structure is illustrated by Fig. 4. but coloured with lithological colour values and are therefore becoming more suitable for users other than solely geologists used to a geological terminology.

Fig. 5. Permeability of rocks (colour version on CD-ROM)

The attribute of Permeability, illustrated in Fig. 5, along with those for Permeability type, Permeability_Max and Permeability_WFD and Sulphate potential, provide a specialised user with a guide to the hydrogeological properties of the rocks.

Fig. 6. Foundation conditions of the rock (colour version on CD-ROM)

This above image (Fig. 6.) shows the nature of the foundation conditions attributed to the rocks and gives an outline guide as to the ground units suitability for construction purposes. Other themes available include Geological Age and an Engineering classification. The Engineering geology attribution is based on the classification scheme developed in thematic mapping projects described elsewhere


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(Forster et al. 2004). The description provides an average value for each modelled formation. The attributed 3D model provides a platform whereby the integration and visualization of data from many different sub-disciplines can be achieved (Royse et al. 2008).

4 The Map Window The Map Window enables the view of geological units in 2D (plan view), individually or collectively, as coverage’s or contoured bases and tops. The Map Window can also display a pre-loaded raster map of the topography for reference, or maps indicating the uncertainty of the model. In the Map Window the user can specify the location of synthetic boreholes and the alignment of synthetic cross-sections. 4.1 Synthetic borehole After selecting the above button in the header bar, a synthetic borehole is created by clicking once at a location in the Map Window where required. To view the result immediately, the borehole window must have already been activated. 4.2 Synthetic cross-section This is invoked by selecting the above button and clicking once on the Map Window. On moving the cursor again a line will appear, anchored to the point, from where the mouse was first clicked. A double-click at another location will complete the cross-section and a red line will appear showing the plan view of the section. A window will also open asking for the newly created cross-section to be named. Once named, the section appears in the Synthetic section window. A synthetic section can be constructed by using as many points as required, but there must be a minimum of two. 4.3 Synthetic Horizontal Slice Activating this button will create a message box asking the user for a depth at which the 3D model will be sliced relative to Ordnance Datum (OD).

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This extract, created from taking a horizontal slice through the model, is displayed in the 3D window. Controls available to the user in this window give the option, by choosing the General Settings tab, to define the background colour from a palette, to toggle the outside frame and cross-hairs on and off and by clicking on the ‘save’ Map icon, to convert the view into a ‘.png’ raster. Opening the TopoMap tab allows user adjustment to the transparency of the topographic raster image in the Map Window. Properties of other maps can be controlled by right clicking on the map and then the transparency can be adjusted in the Object tab. A right click whilst over Geological Unit>Properties reveals the Object tab. The name or code of the selected unit is displayed in bold at the top and the user can select whether to contour the base or top of the unit and set the preferred contour interval in metres. The unit is shown in its pre-determined colour when the extent of unit control is ticked on. The slider bar immediately below varies the transparency. The 3D view settings give the option to display the geological units either as floating contours, a triangulated mesh or colour shaded objects. The bottom slider bar varies the transparency of the 3D colour shaded object.

5 The Synthetic Section Window The Synthetic section Window is populated and active once synthetic cross-sections have been selected in the Map Window using the synthetic cross-section tool. The tool icons on the header bar to this window are identical to those in the Map Window, with one additional option available to specify the vertical exaggeration by a user chosen input. As with the Map Window, the Explorer tab reveals the Table of Contents whilst the Legend tab displays the units present in the section. A right click on the General Settings tab allows the user to define the background colour from a palette. A tick in the ‘scale’ box creates a scaled frame surrounding the synthetic section. The save ‘Profile’ icon gives the option to save the current view as a *.png raster format. A right click on any synthetic section in the table of contents enables the user to set the properties of the section using intuitive controls. The name of the section is shown in bold at the head of the tab.


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Options include the ability to label with the names of the geological units and slider bar variability of the transparency of the section. To view multiple synthetic cross-sections at the same time the user must enter the 3D Window.

6 The 3D Window The 3D Window enables interactive viewing of the model and uses the left and right mouse buttons for all navigation. The model can be rotated by holding down the left button and moving until reaching the required angle. Zooming in and out is achieved by holding down the right button and moving in an upward or downward direction. Panning is invoked by holding down both buttons and moving. Additional tools in the header bar of the 3D Window offer the ability to spin the model and to show a vertical or horizontal view. Each geological unit can also be turned on or off. A right click on an individual unit gives the option to display the ‘Object’ properties tab. The 3D window contains a number of tab menus enabling the user to control various aspects of the model appearance. Opening the General Settings tab allows the background colour to be selected from a palette. It also allows the models ‘frame’ and ‘cross hairs’ to be toggled on or off. The Save ‘3D view’ icon gives the option to save the view in a *.png raster format. Opening the Exploded tab presents a toggle box allowing the explosion of the model, i.e. the separation of individual geological units from others. The tab also allows an expansive directional control over the contents of the exploded view. The Section tab allows the user to view horizontal slices of the model in a north/south direction and separately in an east/west direction. All geological objects must be hidden (geological units>hide all objects) to be able to view the horizontal slices. Opening the Stereo effect on/off tab allows viewing of the model in 3D stereo with a choice of the colour of any stereo glasses available. The TopoMap tab allows the position of the topographical raster in the model to be adjusted along with its transparency.

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7 The Synthetic Borehole window The borehole icon in the top left hand corner will open up the synthetic borehole viewer and the tools carry the same functionality as those in the Map and Section windows with the added ability to drag the borehole image to a user desired location in the display by holding down the left mouse button. The borehole viewer display shows: x The depth to the base of each geological unit relative to Ordnance Datum (OD). x The OD and name of the synthetic borehole at top. x The name of each of the modelled units.

Fig. 7. Example synthetic borehole representation (colour version on CD-ROM)


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References Forster, A. et al. 2004. Applied geological mapping for planning and development: an example from Wigan UK. Q J Eng Geol Hydrogeol 37:301:315 Kessler, H. & S.J. Mathers. 2004. Maps to Models. Geoscientist, 14/10, pp. 4-6. http://www.bgs.ac.uk/science/3Dmodelling/mapstomodels.html Kessler, H. et al. 2005. 3D geoscience models and their delivery to customers. In: Three dimensional geologic mapping for groundwater applications, Workshop extended abstracts, Salt Lake City, Utah, 15 October 2005. Geological Survey of Canada, 2005. p. 39-42. http://crystal.isgs.uiuc.edu/research/3DWorkshop/2005/pdf-files/kessler2005.pdf

Kessler, H. et al. 2009. The capture and dissemination of integrated 3D geospatial knowledge at the British Geological Survey using GSI3D software and methodology. Computers & Geosciences, 35, 1311–1321. http://dx.doi.org/10.1016/j.cageo.2008.04.005 Royse, K. R. et al. 2008. Property attribution of 3D geological models in the Thames Gateway, London: new ways of visualising geoscientific information. Bull Eng Geol Environ

Three-Dimensional Visualisation of the Tectonic movement over Mexico by means of the Global Positioning System (GPS) measurements

Bertha Márquez Azúa1, Ismael Luis Ledesma Tello1, Javier González Sánchez1, Maria Guadalupe Ascencio Escamilla2 1 2

Universidad de Guadalajara, Guadalajara, Mexico Tecnológico de Monterrey, Guadalajara, Mexico

Abstract This paper presents the design of a computer system for visualizing in three dimensions the movement of the Earth’s crust by means of the information gathered and processed from the Global Positioning System (GPS). Several existing products, display information corresponding to the movement of each GPS component (latitude, longitude and altitude) using a set of static two-dimensional graphics. These techniques are useful and understandable to scientists on the topic of study, however, the needs to analyze the information from a different perspective and create a presentation system that achieves the understanding of the phenomenon in a wider audience, are the motivation of this work. The system presented here, has been built to be used by the Department of Geography and Territorial Planning from the University of Guadalajara in the field of motion studies of the Earth’s crust in Mexico. Keywords: 3D visualization, Earthquake Hazards, GPS, JAVA, Modeling, tectonic displacement


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240 Bertha Márquez Azúa, Ismael Luis Ledesma Tello, Javier González Sánchez, Maria Guadalupe Ascencio Escamilla

2 Introduction Get the location of a point on the Earth's surface with great precision is possible using GPS (Global Positioning System). By fixing a GPS receiver station on the ground and continually taking the reading of its position on the earth surface the movement of that place during the time can be revealed (Zumberge 1997). The information obtained permits to build a three-dimensional graphics computer system to model the movement of GPS stations with respect to time, and studies of crustal deformation to visualize the displacement showing the areas represented by each GPS station. (Marquez-Azua, DeMets 2003). Building 3D graphics with time controls and interaction between stations is a tool to understand the movement of the Earth's crust. It helps to improve the understanding of our environment by facilitating the estimation of risks in different seismic zones of Mexico and focus institutional initiatives or programs aimed to the prevention of risks from the seismic and volcanic phenomena, as well as enrich the current theoretical model of plates of the Earth's crust along Mexico and support the needs for further studies in not monitored areas. (Ponce et al. 1992). The case of study for the present work is the project of movement analysis of the Earth's crust (Marquez-Azua, DeMets 2003) being developed at the University of Guadalajara, which analyzes data, from the National Institute of Statistics, Geography and Informatics of Mexico (INEGI), collected daily since 1993 from its network of 15 fixed GPS stations located in different regional offices, thus covering the country (INEGI). For the computer system generated as a result of this work the methodology of the Unified Development Process (RUP) in the category of small models was applied for the software modeling. Since this methodology promotes the adoption of best practices in iterative development processes (Baldwin 2005). The system implementation was developed using the Java programming language and its 3D modeling API and database access (Java Sun). 2.1 Global Positioning System The Global Positioning System (GPS) is a constellation of satellites that constitutes the project NAVSTAR (Navigation Satellite Timing and Ranging), which provide three-dimensional position, navigation and time

Three-Dimensional Visualisation of the Tectonic movement over Mexico by means of the Global Positioning System (GPS) measurements 241

continuously and in real time worldwide. Any person with a GPS receiver can access the system to be used in applications requiring position on any place on Earth, meaning the obtaining the geographic coordinates of a point in space. (Leick 1995). Any position from a GPS receiver contains a degree of uncertainty. The final accuracy is determined by the sum of different sources of error, but these depend essentially on ionospheric conditions, weather and type of equipment used. As a result of a process of correction is possible to know the position on the surface of the GPS receiver, this is, get its coordinates X, Y, Z (North, East longitude and altitude above mean sea level, respectively) (Hurn 1989). The initial accuracy of these measurements permits to determine the position with an error less than 1m in radial direction. However, the final precision grows after the data received is corrected with the information provided by satellite observations from ground control stations, reaching millimetric precision. 2.2 Plate Tectonics The solid outer crust of the globe is divided into sections called "plates". Each of these plates shows movements in different directions which causes strains in the cortex in areas where one plate is separated from other. The deformations of the plates cause sudden earthquakes of different intensities depending on the type, extent and location of the deformation (Cox 1986). Geology of Mexico is the result of multiple tectonic processes that have affected it throughout its evolution. The current geography of Mexico is a result of interaction with the continental block that surrounds oceanic provinces. The Baja Peninsula is separated from the rest of the continent with a movement toward the northwest; on the South Pacific of Mexico, from Cabo Corrientes in the state of Jalisco to Central America, the Cocos oceanic plate is absorbed by the mainland, such subduction occurs along a trench known as Mesoamerican trench. On the other hand, in the geological provinces of the Gulf of Mexico and Caribbean, tectonic stress are cortical separation, also identified as strain or rifting, which are acting on continental margins, they, in turn, advance on the funds deepest ocean basins as a result of displacement of the North American continental tectonic plate to the west, and the Caribbean to the east. These plates are shown in Figure 1.


Fig. 1. Crustal plates that make up the territory of Mexico, its movement, deformation and seismic recording (Marquez-Azua & DeMets 2003)

This involves identifying areas of high seismic risk that dramatically affect the western and southern portions of Mexico, and the intermediate zone known as Transmexican Volcanic Belt (CVT). This belt is one of the major geological structures of Mexico and is located in the center of the country between 96 ° and 106 ° west longitude, with an area of 1000 km long and its width varies between 20 and 200 km. 2.3 National Active Geodetic Network The National Institute of Statistics, Geography and Informatics, operates the National Active Geodetic Network (RGNA) constituted of 15 monitoring stations. Figure 2 shows the location of these stations.


Fig. 2. RGNA: Location of stations (Marquez-Azua & DeMets 2003)

The criterion taken by the INEGI for the distribution of the stations was ensuring national coverage by determining a coverage radius of 500 km per station (INEGI). Monitoring stations are located in the following cities in Mexico: Aguascalientes, Campeche, Chetumal, Chihuahua, Colima, Culiacán, Hermosillo, La Paz, Mérida, Mexicali, Monterrey, Oaxaca, Tampico, Toluca and Villahermosa. All of them physically established on steady structures, which have made precision measurements according to international standards, to define its coordinates. Each network station emits daily information regarding its position and satellite orbits reference files in native format using GPS, every 30 seconds (Gregorius 1996). 2.4 Processing of GPS data To conduct the study presented, is necessary to process the data provided by the stations. The first step is the debug and obtaining precise orbits that will ensure the required millimetric accuracy in the measurements. The native data are obtained from RGNA text files in a independent interchange format called RINEX (Receiver Independent Exchange Format). For the analysis of these data files is used Gipsy-Oasis II, a software developed by the Jet Propulsion Laboratory of NASA. The software allows obtaining the receiver's position with millimetric accuracy after applying various correction methods. The result is a new text file now in STACOV format (STAtion COordenates and Velocity) which contains the X, Y, Z of the station. These coordinates locate a point on the surface


of the earth, corresponding to X to the North latitude, Y to the East longitude and Z to the altitude above the sea level (Gregorius 1996). The study of crustal deformations in Mexico (Marquez-Azua, DeMets 2003) based on data produced by each of the GPS stations of the National Active Geodetic Network of the National Institute of Statistics, Geography and Informatics of Mexico (INEGI) has succeeded in obtaining the XYZ coordinates of each day corresponding to each of the GPS stations from 1993 to 2009. After processing this information is possible to analyze data from GPS stations, such as the case of studies in crustal deformation seek to identify patterns of movement and the impact of these movements (Marquez-Azua, DeMets 2003). 2.5 Graphics and velocity maps Drawing conclusions has relied on the generation of lists containing the XYZ coordinates of each of the stations as well as charts showing the movement of the XYZ components independently, then performing a statistical analysis and is accompanied by maps Mexico showing the location of GPS stations with their respective motion vector representing the magnitude and direction of movement of the station. These maps are called velocity maps and represent the movement (North, East, Vertical) for a day. The velocity maps show a group of stations and their behavior over a period of time. The velocity map of Figure 3 shows the movement patterns of each of the RGNA stations allowing to compare the magnitude and direction of movement of the stations.


Fig. 3. Map of Mexico based on analysis of data from the RGNA, processed from 1993 to 2001 (Marquez-Azua & DeMets 2003)

2.6 State of the Art Currently existing software to analyze and display the GPS information, includes some designed to locate on maps the position of GPS receivers and other specialised systems formed as developed by commercial organisations or research institutes. Some of these programs are focused on visualisation functionality in layers (ESRI), others rely on maps (Pasadena), which show static information on earthquakes and velocity vectors of GPS stations, but do not consider understanding the continuous movement stations with respect to time as it poses the main objective of the project described here. The software Virtual Globe (SINTEF), is a clear example of the basic controls for manipulating graphics that reflect information in three dimensions, as the relief of the crust is.

3 Developed system The design of Three-dimensional modeling system (SMT) seeks to meet the requirement of analyzing the information from another perspective and


create a filing system that achieves results understanding of the phenomenon in a wider audience. 3.1 System Background The input data to the SMT are STACOV format files that the Department of Geography stores and have been the result of a previous processing related to its studies of movement of the Earth's crust. The general process of the SMT system is to transform the input data, according to the customisation parameters defined by users: start and end dates of data and desired stations to generate the graph. The system processes data representing movement of the stations in the range of millimeters per year, assuming these quantities is proposed that representation be made multiplying by a factor to determine until the movement is perceptible. 3.2 Methods Unified Process (UP): This software development process encourages iterative development. This development is a group of mini-systems called short iterations, each of these iterations will be integrated one by one until reaching the desired system. The development of iterations allows feedback and adapting the system, and it is possible to determine (in the first iterations) if the requirements should be modified, such modifications will be made because the implementation of the system is not what the customer really wanted. Java Programming Language: A high-level language object oriented, this would facilitate the work in stages (iterations), maintenance and growth of the software, runs on different platforms and has the ability to generate graphics and animations in two and three dimensions. UML (Unified Modeling Language) standard notation that allows modeling object-oriented systems. Designs generated using this notation diagrams are easy to understand. Database: We implemented a static database, because that this type of database used primarily to store historical data. The stored data set can then be used to study their behavior in certain periods. The data stored in the database are derived from information from the National Active Geodetic Network (RGNA) of the National Institute of Statistics, Geography and Informatics of Mexico (INEGI).


3.3 Results The development of the system meets the requirements and objectives that motivated its implementation. The SMT allows graphical visualisation in two and three dimensions of the tectonic plates movement in Mexico. With such a display is possible that the movements of tectonic plates are analyzed by researchers and students. Figure 4 shows the graphical interface of the system. In the left image you can see the 3D graphics area. The graphic scene contains the outline of the Mexican Republic. Within that contour are located the RGNA stations. Each station is represented by a green and a red sphere, these are connected by a white line to specify that the couple of areas refer to only one station. The green sphere represents the initial position of the station, and that position in the scene graph is fixed. The red sphere represents the position at the time of reproduction of the animation.

Fig. 4. GUI of Three-Dimensional Modeling System

The right side of Figure 4 shows the tool panel and the database panel. The first panel contains two sets of checkboxes, one group of them (Figure 5) corresponds to the stations (areas), when one of the checkboxes is selected you will see on the scene the station referred to that box. The second group of checkboxes (Figure 6) selection controls the display of the coordinates and only will observed during playback those coordinates of the active checkboxes.


Fig. 5. Panel tools, the red rectangle encloses the checkboxes station scene graph (green spheres)

Fig. 6. Panel tools, the red rectangle encloses the checkboxes of the coordinates of the stations (red spheres) that will be visible in the scene graph

The Tools panel contains buttons and sliders to control the elements of the scene graph. Figure 7 shows the controls for selecting dates and implementation of elements of the scene graph. The buttons on this panel section will reproduce the graph, pause, back and forward in time to reproduce or make inquiries of specific dates.

Fig. 7. Panel tools: Date selection controls and graphics performance of the stage

The way we played the animation in the three-dimensional graphics stage is because the red spheres show the position of the station to which they refer a certain date. This position and date is stored in the database. Upon pressing the play button (►) starts reading from the database, retrieves the positions and dates of the stored stations and displays a label on the Tools panel (Figure 8) with the date that corresponds to those positions. The station information and dates mentioned above is organised


by date (lowest to highest) and is in this order that the elements of the scene graph will be played.

Fig. 8. Section tool panel, the red rectangle encloses the label date played in the scene graph

The button that is labeled “consulta” initiates an execution of the positions from the starting date to the end date indicated in the control of dates (Fig. 9).

Fig. 9. Section of the Tools panel. The red rectangle encloses the start and end dates controls that determine the query executed in the scene graph

Figure 10 shows the controls that affect the visual scene graph. The scene graph will rotate in different directions depending on the button you press (in this section of the Tools panel.) Figures 11 and 12 show the visualisation of the scene at different angles.

Fig. 10. Control Panel. The red rectangle contains buttons that control the angle of vision of the scene graph


Fig. 11. Map rotated upwards. It is easier to visualize the direction of the positions

Fig. 12. Map rotated to the right

The section of the tool pane of Figure 13 shows different sliders that affect the scene graph elements. The slider labeled zoom zooms in and out to the scene graph, Figure 14 shows the scene zoomed in. The proportion slider affects the lenght of the white line joining each pair of spheres (green and red), the slider speed increases or decreases the speed at which the positions of each station will move. The last slide has the name “average”, this slider allows you to display the scene graph with the average values of the coordinates (positions) of the stations registered in


the database, the number of averaging the data depends on the value chosen in the slider.

Fig. 13. Panel tools. The red rectangle encloses the sliders that control different functions of the scene graph

Fig. 14. Zoom in to the map, showing two stations, located in the cities of Culiacán and Guanajuato

The bottom panel presents the information tools of any station that is selected (Figure 15), to select a single station must position the cursor on the green area that corresponds to the station. It also fixes the selection for the button “Timeline” or the button “picture” to see pop-chart timeline (Figure 16) or the photo of the station (Figure 17) respectively.


The database panel contains a button to feed the database with new data obtained from RGNA.

Fig. 15. Panel tools. The section enclosed in the red rectangle is the information about the selected station (red circle)

Fig. 16. Graphical timeline of the city of “La Paz” station generated in the SMT system. This chart shows the daily positions of the station from 1993 until 2007


Fig. 17. Photo of the station at Colima. This window appears when you press the photo button and shows the photo of the previously selected station

4 Conclusions and Future Work With the creation of a database and the use of methodologies like the Unified Process, the UML and the Java language we succeeded in the implementation of a system that meets the requirements. This objective is to appreciate the trends of tectonic plate movements using 2D and 3D graphics for the analysis of these movements. The information displayed by the system comes from data collected from GPS stations network named Geodetic Network active National (RGNA). The system presented has the name SMT (Three-Dimensional Modeling System). The SMT can be used as an analytical tool and as a teaching tool. Therefore, the SMT would benefit researchers and students. This system will help to understand the study of crustal deformation processes. The proposed Java-based 3D visualisation has been considered useful by the Department of Geography at the University of Guadalajara to improve understanding of the tectonic movement in Mexico. But now the project seeks to take advantage of the real 3D visualisation technique developed by the company Acotelsa (acotelsa) to see stereoscopic images projected at 2 LCD monitors, a crystal polarised and polarised lenses for the user. Developing the stereoscopic functionality in the SMT system to apply this technique will seek a better three-dimensional perception from the user to make this tool more attractive while preparing for future visualisation capabilities.


References http://www.acotelsa.com, website of acotelsa http://www.apache.org/, website of the Apache Software Foundation open source projects, consulted on 20 June 2005. Richard Baldwin, "Basic Unified Process: A process for small and agile projects" IBM Rational Software (USA, 2005). Alan Cox, Plate Tectonics, (USA: Blackwell Scientific Publications, 1986) http://www.esri.com, official website of the Environmental Systems Research Institute, Inc. (ESRI) accessed January 20, 2005 Gregorius, T, Gipsy-Oasis II How it works, (USA: Department of Geomatics, University of Newcastle, 1996) http://gnuplot.sourceforge.net/demo/binary.html, website tool for noncommercial GnuPlot coordinate graphs in 2D and 3D, accessed March 5, 2005 Home Science: Plate Tectonics, http://www.portalciencia.net/geolotec.html (March 10, 2009). http://java.sun.com/developer/JDCTechTips/2001/tt0530.html, Java Developer Connection (JDC) Tech Tips, May 30, 2001. http://java.freehep.org/demo/LegoPlot /Welcome.html, website of the nonprofit organisation that develops freehep Java 3D tools for studies of highenergy physics, accessed May 10, 2005. Jeff Hurn, GPS to Guide to theNext Utility ", USA: Trimble Navigation, 1989, 76pp http://www.inegi.gob.mx, official website of the National Institute of Statistics, Geography and Informatics of the Government of Mexico (INEGI), accessed January 20, 2005 "XXII International Cartographic Conference (ICC2005, Abstracts of papers), SPAIN. Coruña ICC 2005 Organizing Committee, (July 2005) http://java.sun.com/products/javamedia/3D/, website of the Java 3D API the company SUN Microsystems, accessed 2 May 2005. Craig Larman, UML and Patterns, 2nd edition, Madrid, Pearson, 2003 Craig Larman, "Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development, Third Edition" Pearson Education Inc. (USA, 2005). Alfred Leick, GPS Satellite Surveying, Second Edition ", Wiley'-Interscience (USA, 1995). Marquez-Azua, Bertha. C. DeMets, (2003) "Crustal velocity field of Mexico from continuous GPS measurments, 1993 to June 2001: Implications for the neotectonics of Mexico", USA. Journal of Geophysical Research Vol 108 NO. B9, (September 2003), 2450. http://www.mysql.org/, website software company MySQL AB open source Developers who develops database servers and tools, accessed on 25 June 2005.

Three-Dimensional Visualisation of the Tectonic movement over Mexico by means of the Global Positioning System (GPS) measurements 255 L. Ponce, R. Gaulon, G. Suarez, E. Lomas, Geometry and stress of the downgoing Cocos plate in the Isthmus of Tehuantepec (Mexico: Geophys. Res Lett., 19, 1992). http://pasadena.wr.usgs.gov/scign/Analysis/, website Integrated GPS Network in Southern California, accessed 30 May 2004. http://globe.sintef.no/earthviewcomposite.html/, website of the Globe Virtual Appliance built by the Foundation for Scientific and Industrial Research Norwegian Institute of Technology (SINTEF), accessed 16 May 2004. David Wells, Guide to GPS Positioning, (Canada: Department of Geodesy and Geomatics Engineering University of New Brunswick, 1999). Zumberge, JF., "Precise point positioning for the efficient and robust analysis of GPS data from large networks", Journal of Geophysical Research, 102, 50055017, 1997.

Section 7: Virtual Urban and Rural Landscape Visualization

Terrestrial Laser Scan Application in Urban Planning El Nabbout, K.

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3D Terrain Visualisation for GIS: A Comparison of Different Techniques Che Mat, R., Shariff, A. R. M., Mahmud, A. R. and Pradhan, B.

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Terrestrial Laser Scan Application in Urban Planning

Khaled El Nabbout European Arabic Engineers Union, Chair of the Geosciences Department, Bochum, Germany

Abstract Terrestrial Laser Scan technology was highly developed in the last decade and the application of this technology has been used in different sectors. The aim of this paper is to focus on the strength and weakness of Terrestrial Laser Scan technology especially in the urban planning field. The advantage of such tools based on real application will be presented in addition to data acquisition, processing and visualization. The presentation of the project “Scanning a Road” will give life application too and demonstrate as well the limit of such technology in urban planning applications. The paper will discuss if Terrestrial Laser scan is developed already so far that it can be applied successfully in urban planning. Keywords: 3D Laser scan, 3D city model, Urban planning, Lenticular Foil, Road scanning

1 Introduction Terrestrial laser scan technology has become highly developed in the last decade and the application of this technology has been used in different sectors: Heritage, Industry, Design, Forensic and mainly in land surveying. M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_17, © Springer-Verlag Berlin Heidelberg 2012

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Surveying done by laser scanners essentially results in a density of cloud points where each point has the coordinates x,y and z. The aim of this paper is to outline the strength and weakness of terrestrial laser scan technology in the urban planning field in particular. The advantage of such tools based on real-world applications will be presented in addition to data acquisition, processing and visualization. The presentation of the project “Scanning a Road” will also provide a real-life application as well as demonstrating the limit of this technology in urban planning applications. To what extent has Terrestrial Laser scanning been developed until now and how successfully can it be used in urban planning, especially in the creation of 3D city models or in visualization? The following points will be discussed: the relevance of the terrestrial laser scan; the need for detailed 3D city models; and finally the strengths and weaknesses of such technology.

2. Why use terrestrial laser scanners for 3D city models? Many different kinds of laser scanning systems exist and terrestrial laser scanners on the market include: Time of Flight and the Phase Shift (pointools.com); in the case study of this article, the scanner used was a phase shift scanner. The most recent comparison of various terrestrial lasers scanners on the market was published by GIM-International in August 2009 (refer to volume 23). (FARO news 2008) The idea to look into terrestrial laser scanning for 3D city planning using state of the art mobile mapping systems (laser-scanner.faro.com) was prompted by the speed as well as the accuracy of such technology in data capturing. The recently developed laser scanner photon 120 by FARO offers the fastest and longest-range phase shift laser scanning solution on the market. The FARO photon 120 laser scanner can capture almost 1 million points per second (976,000 pts/second) and can reach an accuracy of 2.mm at 25 m. (Mathias 2009) 2.1 Increasing requests for the 3D model In the last few decades, the topic of 3D was mentioned in almost every subject as the future and as crucially needed. At present, 3D is a part of everyday life, from the use of personal laptops with 3D screens to almost


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every month when we hear of new 3D movies (such as the film Avatar, to take a recent example) (Gandolfi et al. 2008). To focus on the topic of this paper, the need of 3D digital city models is for a digital form which is the same as hard copy. In the market, we find many options for printing 3D models using 3D printers, Lenticular foil or, as Buchroithner mentioned, LFD can offer real 3D displays printed on 1 mm of thickness (Buchroithner et al. 2005). The above-mentioned technologies, all either developed or under development, demonstrate the demand for 3D models and can well support high-quality and precise 3D models. 2.2 Need for more precise and real 3D models Precise and real-world 3D modelling is not only needed, it is necessary spatial in relation to urban planning and especially in highly dense cities and/or old cities where important monuments and heritage sites are protected. Using terrestrial laser scanning can capture highly dense cloud points in very short time either in black and white or colour; some laser scanners have integrated cameras, some of which can be optionally mounted on top with 12 million pixels. The advantage of colourised scanned data is the post-processing when creating 3D surfaces out of the cloud points; this would help to identify every detail and to recognise every small object. The other advantage which precedes the modelling would be the visualization tools; Pointools offers well-developed tools to directly visualise cloud points and to create fly-through models. This tool is fully integrated with GIS and can import shape files and can at same time easily classify the different elevations of each building by supplying the relevant criteria. The other advantage is the ability to measure each of the details in 3D directly on screen, as demonstrated in Fig. 1.( avatarmovie.com)

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Fig. 1: 3D city model viewed from above with classified elevation; and (right) a detailed 3D perspective view. Source: www.pointools.com. (colour version on CD-ROM)

3. Urban Planning Applications The rapid land use/land cover changes taking place in most of the developing as well as the developed countries are part of an intensive urbanisation and industrialisation process (El Nabbout 2007) that makes it necessary to look into effective tools to support the urban planner. Terrestrial laser scanners can play an important role by capturing all the necessary data in an extremely short time while the well-developed visualization tools and first aid tools can assist greatly as a first step in analysing and visualising tools. The subsequent steps would involve 3D modelling, which is definitely time consuming and needs good knowledge. 3.1 How can laser scanners be applied? Terrestrial laser scanning in urban applications for data capturing can be used in 2 ways: 1. by a traditional land surveying process which would replace the Total station or GPS receivers with a laser scanner on the top of a tripod, which could move the scanner from one position to the next. 2. by Mobile Mapping Systems (see Fig. 2). This method was used in many projects, one being the example of the city of Bologna in Italy.


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The laser scanner was mounted upside down on the car with two GPS and distance measurement devices (see Fig. 2 for more details).

Fig. 2: Mobile Mapping Systems, Source: FARO.

Fig. 3: 3D Cloud points over 3D images, Source: Siteco. (colour version on CDROM)

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4. Summary and Outlook This case showed that terrestrial laser scanning can play an important role in urban planning. The outcome of different projects show the suitability of the Terrestrial LS in urban planning and the demand for detailed 3D city models, which can only be accomplished using terrestrial laser scanning. The urban planner should consider the new terrestrial LS applications, especially given the advantage of the visualization tools. Nevertheless, the data modelling is still time consuming and more effective tools are required to automatically transfer cloud points into 3D surfaces, especially with a high number of points. The knowledge necessary to prepare 3D models requires experience and in addition to his CAD modelling, the 3D modeller needs to learn how to transfer such amounts of data into as build maps and 3D real-world models.

References http://www.avatarmovie.com/ Last accessed: 10/05/2010 Buchroithner M. F., Gruendemann T., Kirk R., Habermann K., (2005): Three in One: Multiscale Hardcopy Depiction of the Mars Surface in True-3D. Photogrammetric Engineering & Remote Sensing. October 2005: pp. 1105-1108. El Nabbout k, (2007) Geo-Visualization Tools for Participatory Urban Planning: The Case of Tripoli, Lebanon. Technische Universitaet Dresden, Dresden. FARO news (2008): Scanning a Road, issue 1. Gandolfi S., Barbarella E., Ronci E., Burchi A., (2008): Close Photogrammetry and Laser Scanning using a Mobile Mapping System for the High Detailed Survey of a High Density Urban Area. www.isprs.org/proceedings/XXXVII/congress/5_pdf/158.pdf. Last accessed: 10/05/2010 http://laser-scanner.faro.com/faro-laser-scanner-photon/ Last accessed: 10/05/2010 Mathias L., (2009): Terrestrial Laser Scanners. GIM-International, Vol 23, Issue 8, pp. 20-22. http://www.pointools.com/ptview_features.php Schwarz K.P., El-Sheimy N. (2004): Mobile Mapping Systems–State of The Art and Future Trends, IAPRS, Vol. XXXV, part B5. Siefko S., Robert H. (2004): v3D Terrestrial Laser Scanning as a New Field Measurement and Monitoring Technique. In: Robert H., Rafig A., Robert C. (eds.) (2004): Springer-Verlag, Berlin and Heidelberg, LNES 104, pp. 179– 189.

3D Terrain Visualisation for GIS: A Comparison of Different Techniques

Che Mat Ruzínoor1, Abdul Rashid Mohamed Shariff1, Ahmad Rodzi Mahmud2 and Biswajeet Pradhan3 1

Department of Biological & Agricultural Engineering, Faculty of Engineering, Universiti Putra Malaysia, Selangor, Malaysia. 2 Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor, Malaysia. 3 Faculty of Forestry, Geo and Hydro-Science, Dresden University of Technology, Dresden, Germany

Abstract Geographic Information System (GIS) applications are now moving towards 3D as it has a better representation of the real world. Most GIS applications now can be visualised not only in 2D but also in 3D. Currently most of the applications are capable of operating in an online environment such as Google Earth, Microsoft Virtual Earth and World Wind. Recently, many people use these online applications for their daily work and also for decision making. Terrain visualisation is an important aspect for these three applications, in visualizing the world in 3D. The quality of terrain visualisation depends on the techniques used by the developer. The research for generating good quality terrain visualisation for depicting the real world is ongoing and faces big challenges. There are many techniques available that can be used to visualize the terrain in 3D such as photorealistic and non-photorealistic rendering (NPR). The aim of this paper is to compare different techniques of terrain visualisation in GIS environment. The techniques involved in this experiment are colour shading, terrain overlaid with satellite image and silhouette rendering algorithm for NPR. The comparison is based on the quality of terrain visualisation, representation of object on terrain, representation of slope, and error in terrain. Three different areas in the Universiti Putra Malaysia (UPM) were chosen M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_18, © Springer-Verlag Berlin Heidelberg 2012

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for this experiment; grid Digital Elevation Model (DEM) generated from R2V software was used as topographic data and Quick Bird satellite image of UPM for satellite data. Each of the areas was tested by the three different techniques of terrain visualisation. The results from these different techniques of terrain visualisation are discussed in detail. The results of this paper will be of help to the users in identifying the best technique of terrain visualisation suitable for GIS data. Keywords: GIS, DEM, terrain visualisation, NPR, and silhouette rendering algorithm

1 Introduction In recent years, GIS has become popular among the users of internet technology. This is due to emergence of the new technology of geo-browser. The famous system which falls into this technology is Google Earth. Moreover this system has the capability of providing 3D representation of GIS data to the users, especially 3D terrain. As this system becomes more popular, the demand for 3D data also increases and the user also needs more realism on the 3D data. With this development, the demand for 3D terrain visualisation also increases. However, the quality of 3D terrain visualisation in the existing system is still of low quality. For that reason many researchers are still doing research on this technology with the aim to provide the users with the best quality 3D terrain visualisation, especially for 3D Maps. For example the work on 3D construction of complex geological bodies of Alps (Zanchi et al. 2009) and the visualisation of mount Everest (Gruen and Roditakis 2003) is a good case study to see the effectiveness of modelling 3D terrain especially in the mountainous area. There are many different techniques that could be used for 3D terrain visualisation using GIS which primarily falls into the two categories: photorealistic and non-photorealistic. Hurni and Räber (2004) created the Atlas of Switzerland 2.0 which combines these two categories of visualisation for terrain data. However, this system could be improved for an online implementation. Araya et al. (2002) have proposed BoxLOD technique for effective terrain model based on Virtual Reality Markup Language (VRML) for web based 3D GIS. In term of non-photorealistic, Bratkova et al. (2009) introduced new techniques based on panorama maps for rendering the mountainous terrain. However, the speed of their algorithm is slightly slow. Additionally, researchers are also working on how to reduce the file size of the 3D terrain data for visualisation. For example the work done on


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compression of 3D terrain data using second generation wavelet algorithm (Pradhan et al. 2005, 2006a, 2006b, 2007a, 2007b) can reduced the amount of data set. Based on the above mentioned literature; this paper attempts to compare the different techniques of terrain visualisation for 3D GIS data. The visualisation techniques involved in this experiment are colour shading, terrain overlaid with satellite image and silhouette rendering algorithm for NPR. This paper starts with a discussion on the three visualisation techniques and then suggests which techniques those are suitable for the 3D terrain visualisation in GIS. The paper continues on how the types of data involved, how it is prepared, the specification of the data, and comparison of the three visualisation techniques for the three types of data. At the end, conclusions are drawn which suggests the best 3D terrain visualisation for GIS. The future development of 3D terrain visualisation for GIS data is also made for improving the visualisation techniques.

2 3D Terrain Visualisation for GIS The visualisation techniques involved in this experiment are terrain overlaid with satellite image, colour shading and silhouette rendering algorithm for NPR. 2.1 Satellite Imagery Draped over DTM The technique of overlaying image was first introduced by Brodlie et al. (1992). This technique being adapted by Limp (2000) who used it for overlaying satellite imageries over the GIS layer with attribute information. Then, Shiau, Shiau, & Liang (2007) proposed a new system for creating the 3D environments by combining the Digital Terrain Model and SPOT images of GIS with the weather simulation of the particle system in networking environments. The dead reckoning technique is used to reduce the flow rate of network to make the distributed real-time 3D environment feasible. Brodersen (2005) has demonstrate how geometric mipmap terrain engine can be adapted to efficiently render large scale terrains. At the same time, it allows textures larger than what the graphics hardware is capable of displaying using a single texture. Now most of the GIS software has the capability of performing this technique for implementing the terrain visualisation by overlaying the satellite image over the topography layer. Che Mat, Shariff, & Mahmud (2009) performed research on comparing different GIS software (R2V, Arc View, and Arc GIS) for overlaying satellite imageries over terrain data. They found that Arc GIS is the best software


for performing this process because the satellite imageries are separated into tiles while converting to viewer for visualisation. The quality of 3D terrain visualisation is also very good as compared to other software where the imageries of the object can be identified clearly. This paper uses the technique implemented by Che Mat et al. (2009) for the purpose of comparing the terrain visualisation with other techniques. 2.2 Colour Shading This technique can be classified as the popular technique for visualizing terrain for GIS. Many researchers used this technique for their research. Many GIS software have capabilities on performing this function in their working environment. For example ESRI (2008) in its software, Arc GIS, mentioned that shading can increase the perception of depth in the 3D view and enhance the details of the topography. Other than that, R2V software from Able Software Corp (Able Software 2008) also has the capability of producing the colour shading image from it’s 3D visualisation. This technique is used in this paper for the purpose of comparing the data of terrain visualisation for GIS. 2.3 Silhouette Rendering A number of researchers have worked on interactive non photorealistic rendering of 3D scenes. Silhouette rendering algorithm was considered a part of this technique. For example, the work done by Raskar and Cohen (1999) renders the silhouette edges using a traditional polygonal rendering setup. This rendering technique was implemented by simply pulling the back-facing polygons towards the camera. Lake, Marshall, Harris, & Blackstein (2001) have defined the silhouette as “the edge shared by a front-facing and a back-facing polygons (see Fig. 1). The silhouette in each frame can be found by taking the dot products of the face normal of the two faces adjacent to an edge with the viewing vector (see 1) and comparing the product of these two dot products with zero. If the result of this computation is less than or equal to zero, the edge is a silhouette edge and it is flagged for rendering.”

1

Silhouette Edge = (face normal1.eyevect) * (facenormal2.eyevect) ≤ 0


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Fig. 1: Silhouette edge detection (Image adapted from Lake et al. (2001) )

Northrup and Markosian (2000) introduced a new hybrid technique for rendering silhouette in an interactive way which can be classified as the latest technique. This technique involved sketchy rendering using a combination of image space and object space algorithms. It renders silhouette outlines of 3D polygonal meshes with stylised strokes. The silhouette rendering algorithm used in this paper is adapted from Che Mat and Nordin (2004). This method is called the Wireframe Method and was adapted from Liu (2001). This method involved multi-pass rendering for highlighting silhouette edges. The idea of this method is to render the front facing polygons as a white background and render the back facing polygons as a wireframe. It involved multi-pass rendering for highlighting silhouette edges. This technique results in terrain visualisation which appears to be hand drawn. The pseudo code for this technique is shown below: x Draw background with white colour. x Enable back face culling, set depth function to “Less Than” x Render (front facing) polygons in white. x Enable front face culling, set depth function “Equal To”. x Draw (back-facing) polygons in black wireframe. x Repeat for a new viewpoint.

3 Results and Discussion For the purpose of comparison of different techniques of 3D terrain visualisation, three different areas of UPM were chosen. Fig. 2 shows the image of three different places chosen from the whole UPM area. The first area is the golf course which has the gentlest slopes of the three areas. The second area is public field area which has the second highest steepness of slopes of the three areas and the third area is the research field area which has the steepest slopes of the three areas. Arc GIS software was used for separating these three different areas. After each area had been identified, the SHP file data is sent to R2V software for editing. This is due to the process of clipping the areas, which cause some information about the height of the terrain to be misplaced. Other than that, it also causes the


contour lines to be disconnected from each other. R2V is capable of editing all of these faulty data by comparing it with the original data. The data is then exported back to SHP files and is ready to be used.

Area 3: Public field

Area 2: Research field

Area 1: Golf field

Fig. 2: Three different place chosen from whole UPM area

The criteria of the chosen data are based on number of contour lines which will represent the 3D surface of the area to be compared. These three different areas have different values of height levels and size of the area. The height level and size of area for each area is shown in Fig. 3. Arc Scene is used to measure all of these criteria.

Golf Course Area Height min = 45m Height max = 100m Size of area = 870 m2

Public Field Area Height min = 40m Height max = 85m Size of area = 1,186m2

Fig. 3: Three different topographic areas of UPM

Research Field Area Height min = 45m Height max = 105m Size of area = 1,085m2


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In order to produce three different types of 3D terrain visualisations, two GIS software (Arc GIS and R2V) and one silhouette rendering algorithm is used. The details of each visualisation type are explained in detail in section 2.1 to 2.3. The first visualisation involves satellite data. This data was created by using PCI Geomatica software. Each area of satellite is set as same as the contour data created by Arc GIS. The coordinates of each area is maintained the same between the topographic data and satellite data. If the coordinates are not same, the overlay of satellite image over terrain data cannot be completed, caused by misplaced coordinates. After this process is completed, satellite data can be overlaid onto terrain data by using Arc GIS software. The overlaying process involves several steps; first, data in SHP files from R2V software was opened and added into a new layer. This layer was then converted into Triangular Irregular Network (TIN) format. The next step was to add the satellite image (TIFF format) which was created before into the project. By opening the TIFF layer properties, we can obtain the base heights from the TIN surface as created before. Now the user can view the 3D satellite image on his screen. The data is then converted into VRML file using the Export Scene functions tools. The second visualisation of colour shading is created by using R2V software. After editing the data by using R2V software, it can be visualised the vector data into 3D by creating the 3D grid DEM. The data was then visualised in 3D. This data can be controlled by using 3D controllers such as animation, changing the azimuth value, zoom in, zoom out and also exporting into 3D visualisation such as VRML. The visualisation data is in colour shading mode where the user can see different colours representing the levels of height of the 3D terrain. The third visualisation silhouette rendering algorithm is created by using the existing software develop by Che Mat (2001). This algorithm was introduced by Raskar and Cohen (1999) and adapted by Liu (2001). Borland C++ Builder Version 5.0 was used for developing the application for this algorithm. It was adapting from Raskar and Cohen (1999) demo programme, written in Visual C++. The simple Graphical User Interface (GUI) was built using the Forms on Borland C++ Builder and produced a user-friendly environment for the user. The successful 3D terrain visualisation software for silhouette rendering algorithm was developed and it can read the DEM data. The DEM data for this software is in column format. That is why the DEM grid file data produced from R2V software needs to be converted into the data style which can be read by this software. The conversion programme was done using Visual C++ programming. Lastly, the conversion file was applied into this software and produced 3D terrain visualisation in silhouette fashion. All of the data which represents the


three areas in this research need to go through all of these processes. The results for all these three visualisations are discussed in the next three sections. 3.1 Comparison of 3D Terrain Visualisation for Golf Courses

Satellite overlaid

Colour shading

Silhouette rendering

Fig. 4: Three different image of 3D terrain visualisation for Golf Field Area

Golf course area is the first area compared using the three different techniques of 3D terrain visualisation which are satellite overlaid, colour shading, and silhouette rendering techniques. Fig. 4 shows the results of these three visualisations. The angle and viewpoint for these three visualisations is set at the same point in order to maintain the similarity for comparison. The first image shows the result for satellite overlaid with 3D terrain data. The objects such as jungle, lake, field area, and road can be seen clearly but the height of the area is difficult to clarify. The second image shows the image of 3D terrain in colour shading visualisations. The colour represents different levels of the surface based on the height from the lowest (in dark blue) till the maximum height (in black). But in this image the slope of 3D terrain is difficult to clarify compared to silhouette rendering image which shows the slope of the terrain clearly. Lastly, the third image shows the result of 3D terrain visualisation with silhouette rendering algorithm. The disadvantage of this visualisation is that the lowest area cannot be identified clearly because it only shows the white area. In this area the information of terrain in term of silhouette edge is very low. Some of the slope just represents the slope of terrain as one single line. This is due to the golf course area which has less steep slopes which represents the 3D terrain visualisation.


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3.2 Comparison of 3D Terrain Visualisation for the Public Space

Satellite overlaid

Colour shading


Fig. 5: Three different images of 3D terrain visualisation for the Public Field Area

Public field area is the second area compared with the three different techniques of 3D terrain visualisation. Fig. 5 shows the results of these three visualisations. The angle and viewpoint for these three visualisations was maintained at the same point. The first image shows the result for satellite overlaid with 3D terrain data for the research field area. These areas were surrounded by many fields for research activities in UPM. The objects such as small jungle, cleared area, and roads can be seen clearly. The small road surrounding the small hill can be identified clearly by the user but the slope of the terrain around the small hill is difficult to be identified. The advantage about this visualisation is that the user can recognize almost all objects on the surface of the terrain. The second image shows the image of 3D terrain in colour shading visualisations for the research field area. The levels of height for the terrain is represented by different colours starting from the lowest level in light blue to the highest level which is still in black, same as in the case of the golf course area. This time the slope of 3D terrain was also difficult to be clarified. But the lowest value of terrain is represented clearly by the light blue colour. Compared to silhouette rendering for 3D terrain visualisation, almost the whole area is covered by the white colour. The third image shows the result of 3D terrain visualisation with silhouette rendering algorithm for public field area. The quality of terrain visualisation for this case is almost hand drawn. The information of terrain in terms of silhouette edge is better compared to the terrain visualisation for golf course area. The slope of the terrain is represented by several silhouette edges but not in one single line anymore. This is due to the research field area which has more contour lines compared to contour lines in golf field area.


3.3 Comparison of 3D Terrain Visualization for Research LandParcels

Satellite overlaid

Colour shading


Fig. 6: Three different images of 3D terrain visualisation for the Research Field Area

Research field area is compared with the three different techniques of 3D terrain visualisation. This area mostly covered by several building. Fig. 6 shows the results of these three visualisations for satellite overlaid, colour shading and silhouette rendering. The angle and viewpoint for these three visualisations are still maintained at the same point. The first image shows the result for satellite overlaid with 3D terrain data for research field area. The objects such as small forest, undeveloped area, road, and building can be seen clearly. The quality of terrain visualisation for this area is the same as in the last two areas. The slope of the terrain around the hilly area was difficult to be seen. The second image shows the image of 3D terrain in colour shading visualisations for research field area. The level of height for the terrain is represented by the same colour as in the golf field area. The lowest level is in dark blue and the highest level is in black. The slope of 3D terrain is also difficult to be clarified. But the lowest value of terrain is represented clearly by the dark blue colour. This type of visualisation for the lowest level terrain is better than silhouette rendering visualisation where almost the whole area for lowest height is covered by the white colour. The third image shows the result of 3D terrain visualisation with silhouette rendering algorithm for public field area. The quality of terrain visualisation for this time is looks like hand drawn. The information of terrain in term of silhouette edge is the best compared to the other two areas. The slope of the terrain is represented by many lines of silhouette edges. It was shown clearly that he slope of terrain from the peak to the lowest level. This is due to the research field area which has steeper topography compared to contour lines in the golf course area and the public field area.


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The problem in this visualisation is that when the viewpoint is moved close to the terrain, some of the terrain information is lost and this shows clearly in the images.

4 Conclusions In conclusion, by comparing these three types of visualisations, it can be concluded that each visualisation technique has it own advantages and disadvantages. All of the 3D terrain visualisation involved in this paper can be used for GIS. The satellite overlaid visualisation is good for representing the whole object in the 3D surface as compared to the real data. But the satellite data need to be always updated in order to get the real image of the object in 3D terrain surface. Other than that, the topographic data also needs to be the latest data. The colour shading visualisation is good for representing different values of 3D terrain but if the interval of the contour is closer, better visualisation could be produced which shows clearly the peak area of the terrain. This visualisation is best for presenting the lowest level of the terrain compared to silhouette rendering visualisation. Silhouette rendering visualisation is already approved for visualizing terrain in artistic mode. The silhouette edges represent clearly the slope of the terrain. The highest silhouette edge is better for representing the terrain information. For future work, this visualisation could be combined with satellite overlaid visualisation for creating more futuristic 3D terrain which will highlight the information of the slope on top of the satellite images.

Acknowledgements The authors would like to express their sincere appreciation to the Taman Pertanian Universiti, UPM for providing the satellite image of the UPM area. Our most sincere appreciation and thanks to the National Survey and Mapping Malaysia (JUPEM) which provided the contour data for the UPM area. Without their help this project could not be completed. Thanks to the Prof. Dr. Manfred Buchroithner for his helpful editorial comments which further improved the quality of the paper.


References Able Software (2008) R2V: Advanced Raster To Vector Conversion Software. Accessed 12 December 2008 from http://www.ablesw.com/r2v/ Araya S, Hyunsuk J, Araya R (2002) An Effective Terrain Model for Web-Based 3D Geographic Information Systems. Electronics and Communications in Japan, 85(9), 1153–1161. Bratkova M, Shirley P, Thompson WB (2009) Artistic Rendering of Mountainous Terrain. ACM Transaction on Graphics, 28(4), 1-17. Brodersen A (2005) Real-time visualization of large textured terrains. Paper presented at the 3rd international conference on Computer graphics and interactive techniques in Australia and SouthEast Asia, Australia. Brodlie KW, Carpenter LA, Earnshaw RA, Gallop JR, Hubbold RJ, Mumford AM, (1992). Scientific Visualisation : Techniques and Applications (eds ed.): Springer-Verlag. Che Mat, R. (2001) Evaluation of Silhouette Rendering Algorithms in Terrain Visualisation. Unpublished Master Thesis, Department of Computer Science, University of Hull, Hull. Che Mat, R., Nordin N (2004) Silhouette Rendering Algorithms using Vectorisation Technique from Kedah Topography Maps. Paper presented at the National Conference on Computer Graphics and Multimedia. Che Mat, R., Shariff ARM, Mahmud AR (2009) Online 3D Terrain Visualization: A Comparison of Three Different GIS Software. Paper presented at the International Conference on Information Management and Engineering, Kuala Lumpur, Malaysia. ESRI (2008) GIS and Mapping Software. Accessed 12 December 2008 from http://www.esri.com Gruen A, Roditakis A (2003) Visualization and animation of Mount Everest. Paper presented at the International Workshop on Visualization and Animation of Reality-based 3D Models (ISPRS), Switzerland. Hurni L, Räber S (2004) Atlas of Switzerland 2.0. Paper presented at the 4th ICA Mountain Cartography Workshop, Núria, Spain. Lake A, Marshall C, Harris M, Blackstein M (2001) Stylised Rendering Techniques For Scalable Real-Time 3D Animation. Chapel Hill: Graphics Algorithms and 3D Technologies Group (G3D), Intel Architecture Labs (IAL) University of North Carolina. Limp WF (2000) Put the "Fizz" into "Data Viz". GeoWorld, 13, 40-45. Liu J (2001) Computer Generated pen-and-ink Illustration. Technical Reports Stony Brook: Department of Computer Science SUNY at Stony Brook. Northrup JD, Markosian L (2000) Artistic Silhouettes: A Hybrid Approach. Paper presented at the to appear in proceedings of NPAR 2000. Pradhan B, Kumar S, Mansor S, Ramli AR, Shariff ARM (2005) Light Detection and Ranging (LIDAR) Data Compression. KMITL Science Technology Journal, 5(3).515-526.


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Pradhan B, Kumar S, Mansor S, Ramli AR, Shariff ARM (2006a) A Fast Processing Algorithm for Lidar Data Compression Using Second Generation Wavelets. Korean Journal of Remote Sensing, 22(1), 49-61. Pradhan B, Kumar S, Mansor S, Ramli AR, Shariff ARM (2006b) Spatial Data Compression and Denoising Via Wavelet Transformation. Applied GIS, 2(1), 6.1-6.16. Pradhan B, Kumar S, Mansor S, Ramli AR, Shariff ARM (2007a) GIS terrain data compression using Lifting Scheme- a new direction. International Journal of the Computer, the Internet and Management, 15(2), 9-19. Pradhan B, Kumar S, Mansor S, Ramli AR, Shariff ARM (2007b) Second generation wavelet based GIS data compression using Delaunay triangulation. Engineering Computations, 24(1 and 2), 200-213. Raskar R, Cohen M (1999) Image Precision Silhouette Edges. Paper presented at the 1999 symposium on Interactive 3D graphics, Atlanta, GA USA. Shiau YH, Shiau YH, Liang SJ (2007) Real-Time Network Virtual Military Simulation System. Paper presented at the Information Visualization, 2007. IV '07. 11th International Conference. Zanchi A, Francesca S, Stefano Z, Simone S, Graziano G (2009) 3D reconstruction of complex geological bodies: Examples from the Alps. Computers & Geosciences, 35(1), 49-69.

Section 8: Non-Planar Optical Projections

Cartographic Representation of Dresden’s Historical Development by Projecting a Movie onto a Solid Terrain Model Hahmann, T., Eisfelder, C. and Buchroithner, M. F.

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Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging Trapp, M., Lorenz, H., Jobst, M. and Döllner, J.

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Cartographic Representation of Dresden’s Historical Development by Projecting a Movie onto a Solid Terrain Model

Thomas Hahmann1, Christina Eisfelder1, Manfred F. Buchroithner2 1

German Remote Sensing Data Center (DFD), German Aerospace Center, (DLR) Oberpfaffenhofen, Germany 2 Institute for Cartography, Dresden University of Technology, Dresden, Germany.

Abstract On the occasion of the 800th anniversary of the first mention of the city of Dresden (Germany) a new exhibition for the local City Museum was designed. The intention of the exhibition’s concept was to use modern and innovative exhibits to attract a broad audience. A key element of the exposition is a 2.00 m by 1.50 m solid terrain model of the Dresden Elbe valley. A film, which shows the development of the depicted region since the year 8000 B.C. is projected onto the terrain model by a video projector and the help of a tilted mirror. This true 3D installation is one of the first of its kind worldwide. It facilitates much more thematic flexibility than terrain models without changing illumination. Both the terrain model and the film result from a cooperation of the City Museum of Dresden with the Institutes for Cartography and for Software- and Multimedia-Technology of the Dresden University of Technology. The scale of the solid terrain model is 1:16,250. It is four times vertically exaggerated to improve the perceptibility of small terrain features for the visitor. The projected film is a FlashMX animation, for which several tenths input data layers were prepared with the GIS software ArcGIS and the vector graphic software Freehand. Input data for M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_19, © Springer-Verlag Berlin Heidelberg 2012

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Thomas Hahmann, Christina Eisfelder, Manfred F. Buchroithner

both the solid terrain model and the animation were Laserscanning DEM data and ATKISDGM/- DLM data. A major challenge of the terrain model construction was the reconstruction of the primordial terrain. As the input data showed the contemporary situation of the terrain a significant number of visible anthropogenic terrain changes, such as bridges, railway lines, motorways and man-made riverbeds had to be removed. An iterative semi-automatic approach was developed, which cuts relevant areas from the data and using a linear TIN interpolation that filled the data holes afterwards. The filtered data set was cut into a polyurethane pattern plate by using a Portatec milling machine by the Institute for Production-Technology of the Dresden University of Technology. In a stepwise process an accuracy of 1/100 mm in the three dimensions x, y and z was reached. Afterwards the solid terrain model was varnished with a special white colour, for which previous tests had shown optimum reflection behaviour. Keywords: solid terrain model, true 3D installation, DEM data filtering, Cartographic computer animation, Dresden Elbe Basin, height exaggeration, ATKIS DLM + ATKIS DGM, Geo to CAD data conversion

1 Introduction Museums have the mission to provide information in a general understandable way and should consider the principles of museumdidactics. Furthermore in these days the keywords of New media and Multimedia have found their way in the concepts of exhibition planning. These two aspects highly influenced the design of the installation that is described in this chapter. The installation is an outcome of a cooperation of the City Museum of Dresden and the Dresden University of Technology. For the newly designed exhibition of the museum, “Dresden macht Geschichte“ (opening in November 2006) a range of exhibits was produced by students of the University. One of these installations is a solid terrain model of the Dresden Elbe Basin (Hahmann 2006). A video projector is used to project a film onto the terrain model. The film shows some aspects of the development of the Dresden area since the year 8000 B.C. (Peisker 2006, Pentzold 2006, Stadtmuseum Dresden 2010). This installation may be referred to as an animated real-3D-genesis-cartography with audio explanation (Buchroithner 2007).

Cartographic Representation of Dresden’s Historical Development by Projecting a Movie onto a Solid Terrain Model 283

A solid terrain model (sometimes referred to as geosculpture or topographical model) is a physical replication of smaller or larger sections of the Earth‘s surface, which is exactly to scale (Imhof 1972). Following Bollmann and Koch (2002) several types of solid terrain models may be distinguished. These are models produced by the so-called sandbox method, levelled reliefs that show the contour lines, and most advanced, Modelled solid terrain models. For comprehensive descriptions of the historical development of the creation and use of solid terrain models the reader is referred to Imhof (1981) and Caminada (2003). Only a short overview shall be presented here. In the Middle Ages the first models of castles and fortresses were produced mainly for military purposes. One of the first known solid terrain models made by Franz Ludwig Pfyffer in the years 1762-1786 shows Central Switzerland. According to Imhof (1981) “the most beautiful solid terrain model of the most beautiful mountain on Earth” was created by Xaver Imfeld. This model depicts the Matterhorn (1896, scale: 1:5,000). For his famous model of the Bietschhorn (1939, scale: 1:2,000) Eduard Imhof was one of the first to use stereo aerial images for the exact model creation. His motto was: “The final model shall be that lifelike that its photographs perfectly simulate reality” (Imhof 1981). The biggest exhibition of historical solid terrain models can be visited in the Swiss Alpine Museum in Berne. More than 270 models are under display (Alpines Museum 2010). Today hand-made solid terrain models are produced only by a few artists. Toni Mair from Switzerland is one of them (Mair 2010). Nowadays most models are machine-made (e.g. Solidterrainmodeling 2010). Imhof (1965, 1972) lists some advantages of solid terrain models. They show a high degree of detail and exactness and are better understandable than virtual computer models and analogue maps. The models allow a direct plastic perception without the necessity to read contour lines. Directions, surface features and viewing points are directly visible. Furthermore solid terrain models may be viewed with changing illumination. Many simultaneous observers can view the models from arbitrary viewing points, and different surface features can be simultaneously perceived. The probably most important characteristic is the possibility of direct interaction with the model; surface features can be touched by the visitors. This haptic interaction capability makes solid terrain models perfectly suitable for museums and school education, especially within the subjects of e.g. geography, geology, and geomorphology (Imhof 1972). Buchroithner (2007) summarizes that an increased attractiveness and acceptance of such real three-dimensional

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landscape depictions can be observed in comparison with flat twodimensional maps. All these benefits explain the frequent use of solid terrain models in museums and exhibitions. An important aspect of solid terrain models is the use of an appropriate height exaggeration factor. Height exaggeration is defined by the increase of the vertical scale with respect to the horizontal scale. It is used to produce an increased visual perceptibility of height differences on the model. According to Imhof (1972) height exaggeration is in contradiction to a lifelike appearance of the solid terrain model and should thus be avoided. The only exception should be didactical reasons. In our project small test models of a subset of the Dresden Basin were produced using the exaggeration factors two, three, and four and visually compared regarding their relief impression (Fig. 1). This led to the decision to produce a four times exaggerated model as with this exaggeration factor the terrain features were best perceptible (Hahmann 2006).

Fig. 1. Small subsets of the Dresden Elbe Basin model that were produced to test the relief impression of different height exaggeration factors

It is worth mentioning that at the Institute for Cartography of the Dresden University of Technology a lot of expertise regarding solid terrain models is available. E.g. a combination of a solid terrain model of a part of the Austrian Alps and an interactive flight over the model was produced by this institution (Buchroithner 2005, Hollinger 2005). The main challenge for the Dresden project was the reconstruction of the primordial terrain of the Dresden Basin. As the input data (section 2) showed the contemporary state of the terrain a significant number of visible anthropogenic changes, such as bridges, railway lines, motorways,


and man-made riverbeds had to be removed. Details about the DEM filtering step and the DEM milling are provided in section 3. In section 4 the details of the installation of the model in the museum exhibition are described.

2 Data This section briefly describes the input data that were used for the production of the solid terrain model of the Dresden Elbe Basin. Two kinds of digital elevation data were available for this project. On the one hand ATKIS DGM 25 data with 20 m horizontal resolution and 20 cm vertical resolution, on the other hand laser scanner data (Maas 2005) with 5 m horizontal resolution and 1 cm vertical resolution. The ATKIS DEM dataset was available in raster format (GeoTIFF), whereas the laser scanner data was available in ASCII point file. The ATKIS DGM 25 data was provided by the Federal Surveying Office of Saxony (ATKIS DGM 2010). The laser scanner data was provided by the Municipal Surveying Office of the city of Dresden. Filtering of buildings and vegetation had already been performed for this dataset during pre-processing. Whereas the coarse resolution ATKIS data covered the whole area of interest the high resolution laser scanner data only covered the extent of the city of Dresden (Fig. 2).

Fig. 2. Map showing the spatial extent of the available input DEM datasets and the Solid Terrain Model of the Elbe Basin

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Auxiliary data that were used for this project, especially for the filtering of the DEM data, included ATKIS DLM data provided by the Federal Surveying Office of Saxony (ATKIS DLM 2010). These vector GIS data included e.g. highways and other roads, railway lines, bridges, rivers, and lakes. For the detection of regions, which were affected by anthropogenic terrain changes, suitable historic maps had to be used. A comprehensive review of existing historic maps of the Dresden area is given by Stams (1994). For this project historic maps dating back to three different years were analysed. The most historic map available was the ‘Oberreit-Atlas’ (Section Dresden, Blatt 10, scale 1:57,600, 1843 and Section Großenhayn, Blatt 4, scale 1:57,600, 1843). Further maps that were used are the ‘tenkarte’ (Section Dresden, No. 66, scale 1:25,000, 1887) and the ‘Saechsisches Messtischblatt’ (Blatt Dresden, No. 66, scale 1:25,000, 1910) (Fig. 3). All these maps were scanned and provided by the Map Collection of the Saechsische Landesbibliothek Dresden (SLUB Dresden 2010). Some of these maps have also been digitally reproduced and are available online (Kartenforum Sachsen 2010).

Fig. 3. Small subset of the Aequidistantenkarte (section Dresden, No. 66, 1887, left) and the Saechsisches Messtischblatt (section Dresden, No. 66, 1910, right)


3 Data processing

3.1. Data preprocessing The laser scanner data was imported from the ASCII file format to a GeoTIFF raster file format using the software Microstation Terrascan. The elevation values of both DEM datasets were converted from metre respectively decimetre to the common vertical unit centimetre using ArcGIS software. The horizontal resolution of both DEM datasets was harmonised to 5 m. Afterwards the DEM datasets were fused using the Erdas Imagine software. The ATKIS DLM vector datasets were converted from Shapefile format to the coverage format using the ArcInfo software. Finally the DLM data were cut along the borders of the area of interest. 3.2 DEM data filtering Where people settle they influence the terrain. Drainage channels are excavated; lakes and reservoirs are constructed as well as roads and railway lines with road cuts, embankments, and bridges. Airstrips need a flattened terrain over a quite large area. All these anthropogenic changes of the terrain are visible in the contemporary DEM data. The requirement for the solid terrain model of the Dresden basin was however to depict the primordial terrain with a minimum of visible anthropogenic influences. In Fig. 3 a variety of terrain changes since the end of the 19th century are shown. In the area of Dresden-Friedrichstadt a number of anthropogenic changes are visible, such as the Albert port, the Elbe bayou, the freight depot, and the city railway. Also a major change of the drainage network with the relocation of the Weißeritz occurred in this part of the city. The challenge for the construction of the terrain model was to remove all these topographical objects from the input DEM data (Fig. 4).

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Fig. 4. Overview of the topographic objects that were filtered from the input DEM dataset

For a detailed description of the developed procedure the reader is referred to Hahmann (2006, especially section 5). The DEM data filtering was performed in a stepwise process. First highways, then railway lines and water bodies were removed. In a final step remaining objects such as bridges, hills of debris, or gravel pits were filtered. Historical maps (e.g. Fig. 3) were used for a visual change inspection in addition to the ATKIS DLM data that could be used in a semi-automatic filtering method.


Fig. 5. Sobel filter image of the original DEM prior to the DEM data filtering

Fig. 6. Sobel filter image of the final DEM after the DEM data filtering

In the following, we describe the filtering of a section of a railway line, as an example. A buffer polygon is created around the railway line (ATKIS DLM data) using an empirically found buffer width. The buffer polygon is then converted to a raster dataset (grid) and the arc density of the buffer polygon is increased to 2.5 m. Afterwards, elevation values from the DEM dataset are assigned to the buffer polygon points. Based on these points a TIN (Triangulated Irregular Network) is calculated, which is

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subsequently converted to a raster dataset (lattice). Finally, the original DEM values within the buffer polygons are replaced by the interpolated new DEM values. The buffer widths that were found to be suitable are 45 m for highways, 30 m for railway lines and small water bodies, and 60 m for large water bodies. Edge enhanced images were calculated using the Sobel filter to check the success of each filtering step. When comparing the Sobel filter images calculated prior to the DEM data filtering and after the final filtering step it is clearly visible that most of the relevant anthropogenic terrain changes could be removed successfully (Fig. 5 and 6). 3.3 Milling of the solid terrain model The solid terrain model was produced by the Institute for ProductionTechnology of the Dresden University of Technology. For a direct data conversion from the TIFF format to a CAD data format like IGES or STEP no suitable software was available. Therefore, data exchange had to be done via the neutral ASCII text file format (each single raster points in xyz in one line). Starting from the ASCII format the data could be converted to a special CAD file format that was readable by the milling machine. A Portatec milling machine was used to cut the solid terrain model into a polyurethane pattern plate (Fig. 7). The SikaBlock pattern plate was chosen because it is especially suitable for solid terrain models: It has a high stability, a good milling capability, a good varnishability, and a smooth surface. In a stepwise production process an accuracy of 1/100 mm in the three dimensions x, y, and z was reached. The whole area was first digitally cut into 100 parts with each having a size of 20 cm by 15 cm. Then the milling was performed in three phases: 1) with 20 mm diameter of the milling cutter working along the contour lines, 2) with an 8 mm diameter tool, and finally 3) with a 5 mm diameter tool especially for the milling of narrow valleys. After the finalisation of the milling process the solid terrain model was varnished with a special white colour (RAL 9010, Reinweiß), for which previous tests had shown optimum reflection behaviour (Hahmann 2006).


Fig. 7. Production of the solid terrain model using a Portatec milling machine

4 Installation in the museum The setup of the installation in the museum consists of the solid terrain model, a video projector, and a tilted mirror (Fig. 8). The tilted mirror is used to improve the projection characteristics. It enables to increase the projection distance to about 4 m, which leads to less shadowed areas on the terrain model. It could be shown that the projection geometry allowed for almost complete illumination of the solid terrain model. The hidden area that cannot be directly illuminated has the size of a One-EurocentCoin (2.1 cm²). This corresponds to only 0.006% of the area of the terrain model (Hahmann 2006). An additional advantage of the horizontal positioning of the video projector is the improved air ventilation capability. The dimensions of the final solid terrain model comprise a horizontal scale of 1:16,250, a vertical scale of 1:4,062 (due to the exaggeration factor 4), a West-East-Extension of 32.5 km, and a North-South-Extension of 24.375 km. Its size is 2.00 m by 1.50 m with a height of 8.1 cm (Fig. 9 and 10). For the projection of the movie onto the solid terrain model a DLP video projector with a resolution of 1400 x 1050 pixels (SXGA+) is used. This type of video projector features a long lifetime (up to 4,000 hours), a natural colour impression and a good contrast with a deep black colour when compared with LCD video projectors.

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Fig. 8. Setup of the installation in the museum consisting of a video projector, a tilted mirror and the solid terrain model

The creation of the movie “Dresden, die Entwicklung einer Stadt” was a co-production of Sabine Zimmermann of the City Museum of Dresden (Story / Management / Data research) and two students of the Dresden University of Technology: Editing and processing of historical maps and other data (Peisker 2006) and Computer animation of the movie (Pentzold 2006). The two movies that were produced are online available (Zimmermann 2010). The length of the movies is 11:20 min (full version) and 3:10 min (short version). The creation of the solid terrain model described in this chapter was done by Hahmann (2006). This true 3D installation including the solid terrain model and the projection of a film is one of the first of its kind worldwide. It facilitates much more thematic flexibility than terrain models without changing illumination, which are e.g. printed with natural landscape colours (Fig. 9 and 10).


Fig. 9. View of the final solid terrain model in the exhibition of the City Museum of Dresden, projection of the Elbe River and a historic city extent

Fig. 10. View of the final solid terrain model, Projection of the Elbe River and the potential natural vegetation of the Elbe Basin

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References Alpines Museum (2010) available online at: http://www.alpinesmuseum.ch/index.php?article_id=56&clang=0 (Last accessed 30 March 2010) ATKIS DGM (2010) available online at: http://www.landesvermessung.sachsen.de/inhalt/produkte/atkis/dgm/dgm.html (Last accessed 30 March 2010) ATKIS DLM (2010) available online at: http://www.landesvermessung.sachsen.de/inhalt/produkte/ atkis/dlm/dlm.html (Last accessed 30 March 2010) Bollmann J, Koch WG (eds) (2002) Lexikon der Kartographie und Geomatik. 2 Bde. Spektrum Akademischer Verlag, Heidelberg / Berlin Buchroithner M (2005) Interactive Real-Time VR Cartography. Proceedings of the XXII International Cartographic Conference, A Coruña, Spain Buchroithner M (2007) Echtdreidimensionalität in der Kartographie: Gestern, heute und morgen. Kartographische Nachrichten, 57(5), pp 239-248 Caminada P (2003) Pioniere der Alpentopographie. Die Geschichte der Schweizer Kartenkunst. AS Verlag, Zürich Hahmann T (2006) Bearbeitung digitaler Geodaten für ein Reliefmodell des Dresdner Elbtales. Unpublished Seminar paper, Institute for Cartography, Dresden University of Technology Hollinger A (2005) Kostenloser Flug durch den Nationalpark Gesäuse. Im Gseis. Das Nationalpark Gesäuse Magazin, Frühjahr 2005, p 28 Imhof E (1965) Kartographische Geländedarstellung. Walter de Gruyter, Berlin Imhof E (1972) Thematische Kartographie. Lehrbuch der Allgemeinen Geographie. Walter de Gruyter, Berlin / New York Imhof E (1981) Bildhauer der Berge. Ein Bericht über alpine Gebirgsmodelle in der Schweiz. Schweizer Alpen-Club, Bern Kartenforum Sachsen (2010) available online at: http://www.deutschefotothek.de/#|2 (Last accessed 30 March 2010) Maas H-G (2005) Akquisition von 3D-GIS-Daten durch Flugzeug-Laserscanning. Kartographische Nachrichten, 55(1), pp 3-11 Mair T (2010) available online at: http://www.mair-relief.ch/relief.php (Last accessed 30 March 2010) Peisker T (2006) Geodatenerfassung und -bearbeitung für eine animierte Visualisierung der Siedlungsgenese des Dresdner Elbtals. Unpublished Seminar paper, Institute for Cartography, Dresden University of Technology Pentzold B (2006) Zu den technischen und gestalterischen Anforderungen an dynamische Bilder bei Projektion auf eine waagerechte, unebene Fläche sowie bei freiem Betrachtungsstandpunkt. Unpublished Seminar paper, Institute for Software- and Multimedia Technology, Dresden University of Technology SLUB Dresden (2010) available online at: http://www.slub-dresden.de/en (Last accessed 30 March 2010)

Cartographic Representation of Dresden’s Historical Development by Projecting a Movie onto a Solid Terrain Model 295 Solidterrainmodeling (2010) available online at: http://www.solidterrainmodeling.com (Last accessed 30 March 2010) Stadtmuseum Dresden (2010) available online at: http://www.museen-dresden.de (Last accessed 30 March 2010) Stams W (1994) Die sächsischen Elbstrom-Kartenwerke – ein Überblick. Kartographische Bausteine, vol 9, Institute for Cartography, Dresden University of Technology, pp 39-51 Zimmermann S (2010) available online at: http://www.aktivmuseum.com (Last accessed 30 March 2010)

Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging

Matthias Trapp, Haik Lorenz, Markus Jobst, Jürgen Döllner Hasso-Plattner-Institut, University Potsdam, Potsdam, Germany

Abstract Stereo rendering, as an additional visual cue for humans, is an important method to increase the immersion into 3D virtual environments. Stereo pairs synthesized for the left and right eye are displayed in a way that the human visual system interprets as 3D perception. Stereoscopy is an emerging field in cinematography and gaming. While generating stereo images is well known for standard projections, the implementation of stereoscopic viewing for interactive nonǦplanar singleǦcentre projections, such as cylindrical and spherical projections, is still a challenge. This paper presents the results of adapting an existing imageǦbased approach for generating interactive stereoscopic nonǦplanar projections for polygonal scenes on consumer graphics hardware. In particular, it introduces a rendering technique for generating imageǦbased, nonǦplanar stereo pairs within a single rendering pass. Further, this paper presents a comparison between the imageǦbased and a geometryǦbased approach with respect to selected criteria. Keywords: Stereoscopic Imaging, Non-planar projections, Real-time rendering


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Matthias Trapp, Haik Lorenz, Markus Jobst, Jürgen Döllner

1 Introduction An increasing number of applications and systems use 3D geovirtual environments (GeoVEs) to integrate, manage, and visualize complex geospatial information. They are typically based on virtual 3D city models and landscape models, which have been standardized by CityGML (Kolbe 2009) recently. Modern geoǦmedia technology, such as cylindrical projection walls or multiǦprojector nonǦplanar displays (Fig. 1), enables a more intuitive access of geoinformation to broader audiences and for new fields of applications. In contrast to standard 3D applications, their implementation is based on nonǦplanar projection (Trapp, Döllner 2008; Lorenz, Döllner 2008). As a characteristic feature, geomedia technology provides interactivity, high fieldǦofǦview (FOV), and high image resolution, which facilitates the immersion of the user. Further, stereoscopic imaging improves this immersion effect. While planar stereoscopy is well understood and supported by modern rendering systems, stereo rendering under non-planar projections still receives much less attention and rises a number of conceptual and technological challenges, which we would like to address in our contribution.

Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging 299 Fig. 1: An example of anaglyph stereorendering under cylindrical non-planar projection demonstrates the usage of 3D stereoscopy in combination with large display technology. (colour version on CD-ROM)

From a cartographic point of view, immersion environments are wellǦsuited as a tool for the effective transmission of complex geoinformation embedded in virtual spaces. Especially psychological depth cues support the intuitive understanding of geoinformation. One main psychological parameter describes the retinal image size. Any restriction of the image size on the retina makes the information transmission less immersive, because any surrounding around the presentation area has an impact on the user’s perception. Large projection walls and multiǦprojector presentation areas enhance retinal image size and, therefore, support psychological depth cues. NonǦplanar projections together with stereoscopic imaging further improve the degree of immersion. In this contribution, we discuss with a discussion of the theoretical background of stereoscopic imaging and its application to nonǦplanar projections in the context of cartography and visualization. Next, we present different approaches to interactive stereoscopy rendering techniques for largeǦscale GeoVE under nonǦplanar projections, including both imageǦbased and geometryǦbased approaches, which can be implemented on 3D consumer graphics hardware. We show how these techniques can be applied to passive stereo display techniques, such as anaglyph (Fig. 1 and Fig. 7), polarized, and chromaǦdepth (Fig. 8), as well as to active stereo display techniques. In addition, we conduct a performance comparison and discuss the respective advantages and disadvantages. The remainder of this paper is structured as follows. Section 2 briefly describes the adaption of two rendering techniques for creating stereoscopic nonǦplanar projections. Section 3 presents application examples of the stereoscopic imageǦsynthesis for 3D geovirtual environments. Finally, Section 4 concludes this work.

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Fig. 2: Conceptual framework for rendering stereoscopic variants of planar and non-planar projections.

2 Stereoscopic Rendering for Non-Planar Projections This section deals how to adapt existing realǦtime rendering techniques for nonǦplanar projections to output stereo image pairs. Regardless of the rendering techniques used for creating nonǦplanar projections (NPP), the creation of stereoscopic views comprises the following two basic steps (Fig. 2): 1. Image Generation: The NPP for the left and right images are synthesized by using imageǦbased or geometryǦbased rendering techniques. 2. Stereo Rendering: The stereo pairs are combined into a single frame buffer (passive stereo) or rendered into two frame buffer (active stereo) by using postǦprocessing compositing passes. Besides approaches for omniǦdirectional nonǦplanar projections and camera systems (Peleg et al. 2001) that stitch realworld images to obtain a still stereo image, we find approaches for stereo rendering on multiǦprojector systems (Bimber et al. 2005). This work reflects nonǦplanar projections for single projection centers which can be created using imageǦbased (IBA) and geometryǦbased (GBA) approaches. In this work, we focus on the last two. 2.1 Stereoscopic Viewing To achieve angle and depth disparity that create the stereo effect when viewing, the scene has to be rendered from two virtual eye positions. The eye separation is a distance d in world space. The average distance between the two eyes is 2d = 6.5cm. Given a virtual reference camera orientation C = (P, T, U), we have to derive the camera settings for the left CL = (PL , TL , UL) and right eye CR = (PR , TR , UR). Current applications use three different methods (Bourke, Morse 2007) to obtain these orientations (Fig. 3) by maintaining the upǦvector U = UR = UL:

Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging 301

x Parallel Camera Mode: In parallel mode, the camera position is shifted along the baseline by maintaining the lookǦto direction T = TL = TR. The direction of the baseline corresponds to the right vector R = U x L. This results in new orientations for the left camera: CL = (P – dR, TR ,UR) and right camera CR = (P + dR, TL, UL). x ToeǦǦIn Camera Mode: Additional to the shift of the camera position, the toeǦin mode adjusts the lookǦto vectors with respect to a focal distance df. The respective lookǦto vectors are defined as follows: TL = |(P+ Tdf ) – PL| and TR = | (P+ Tdf ) – PR |. x OffǦǦAxis Camera Mode: This mode is similar to the parallel camera mode but uses a non symmetric camera frustum as described in (Bourke, Morse 2007).

Fig. 3: Comparison of the parameterizations for the parallel, off-axis, and toe-in camera orientation modes for generating stereo pairs. (colour version on CDROM)

2.2 Adapting the Imagebased and Geometrybased Approach These rendering techniques are mainly based on two phases. First, a raster representation of the virtual scene is created using offǦscreen rendering. In the second phase, this representation is used to create different projections or image distortions using image warping in a post processing step (Yang et al. 2005). In (Trapp, Döllner 2008) a generalization of this approach is described that uses a cube map texture to represent the virtual environment and create multiple NPPs and variants of image distortions. Fig. 4 shows an exemplary rendering pipeline for the imageǦbased creation of two stereo mates. More details of this approach can be found in (Spindler et al. 2006).

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t

Fig. 4: Pipeline for the stereoscopic rendering of imageǦbased nonǦplanar projections. (colour version on CD-ROM)

A straightǦforward GBA implementation simply projects all mesh vertices nonǦplanarly and rasterizes the primitives immediately (Spindler et al. 2006). The inadequate linear interpolation during rasterization requires highly tessellated meshes for artifactǦfree renderings. Dynamic mesh tessellation based on instancing (Boubekeur, Schlick 2008; Tatarinov 2008), geometry shaders (Lorenz, Döllner 2008), or hardware tessellation units (Tatarchuk 2007) can ensure this property for arbitrary meshes. An alternative approach is tessellating the nonǦplanar projection into smaller and simpler projections. (Hou et al. 2006) describes an approach for rendering arbitrary projections which is conceptually based on beam tracing. In (Lorenz, Döllner 2009), restrict the constituting projections to being perspective. This enables the direct use of GPU rasterization capabilities, but limits the results to single center projections. Based on that technique, Fig. 5 shows an overview how image pairs can be created within a single rendering pass.

Fig. 5: Adaptation of the geometry-based approach for rendering stereoscopic non-planar projections.

2.3 Comparison We can compare the geometryǦbased and imageǦbased approach with respect to the following criteria:

Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging 303 Stereo Functionality

The imageǦbased approach is limited to generating directional panoramic views because the raster representations are created with a fixed base line for each camera orientation. Following to that, the angle disparity is zero for views along the baseǦline and the user observes only depth disparity. However, the geometryǦbased approach is able to create full 360° OmniǦdirectional stereo panorama. Further, the GBA is capable of supporting all three camera modes described in Section 2.1 without artifacts. The IBA is limited to the parallel camera mode to avoid artifacts in the stereo pairs. Thus, the GBA has a clear advantage over the IBA. Rendering Performance

Table 1 shows a comparison between IBA and GBA with respect to the number of input primitives. Both rendering techniques require only a single scene rendering pass for passive stereo viewing of a single cylindrical projection with a horizontal FOV of 180° and a vertical FOV of 90°. The IBA uses cube map face culling to render only necessary faces. The measurement shows that the GBA performs better than the IBA for low to medium model complexity. For a higher model complexity, both approaches obtain similar nonǦrealǦtime performance but GBA is still faster. In the most common case of rendering a single NPP, GBA should be preferred over the IBA. Table 1: Performance comparison in framesǦperǦsecond (FPS) between the imageǦbased (IBA) and geometryǦbased (GBA) stereoscopic rendering approaches with respect to the geometric complexity (triangles) of a virtual scene.

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Image Quality

The main drawback of the IBA is imageǦquality. In contrast to GBA, sampling artifacts are introduced while creating the projections. This is especially problematic for wireǦframe renderings or NPR techniques such as hatching or similar ones. Fig. 6 shows the different image quality of both approaches. The quality of the displayed image also depends on the projector systems. However, the GBA is superior over IBA because of its output quality.

Enhancing Interactive NonPlanar Projections of 3D Geovirtual Environments with Stereoscopic Imaging 305 Fig. 6: Comparison of the image quality between the geometry-based (left) and image-based approaches (right). The screen shots are conducted using a cube map texture of 20482 pixels on a target resolution of 1600 x 1200 pixels. (colour version on CD-ROM)

Memory Footprint

A further criterion considers the memory footprint for data related to the rendering technique, e.g., texture size and geometry. This is an important criterion for applications that use outǦofǦcore rendering mechanisms. The footprint of the IBA can be considered constant. It depends on the texture resolution s, the precision per colour channel b, the number of colour channels c, and the number of raster layers l. The footprint can be approximated by: OIBA(l,s,b,c) = 2lcbs2 byte without mipǦmaps. This parameterization enables the user to balance the tradeǦoff between image quality and space as well as runtime complexity. Adapting texture resolution according to a projection is problematic, since rasterization speed is optimal for rendering targets sized with powerǦofǦtwo. The memory footprint of the GBA is dynamically view depended and scales linearly with the number of input triangles t. Further, memory footprint depends on the average rate of primitive amplification r (for a 180° cylindrical projection r = 1.5Ǧ2), and the size of each triangle in an intermediate data structure i = 16. The amount of additional memory can be approximated by: OGBA(t, r, i) = tri. Following to that, the space complexity of the GBA is independent of rendering a single NPP or a stereo pair of NPP. For the complex model (3,210,162 triangles) the additional memory requirement for a 180° panorama projection is OGBA ~ 69 MB. This corresponds to four RGBA raster layers with 10242 pixel resolution. Thus, for a higher FOV: OGBA < OIBA is valid in any case. Implementation Complexity

This is a subjective criterion and is included for the sake of completeness. Both approaches rely on programmable GPU (geometry shader functionality). The GBA uses transform feedback that is available on current graphics hardware (Blythe 2006). IBA can be considered as easy to implement and integrate into existing rendering frameworks but needs to apply custom cubeǦmap sampling. Since the IBA is independent of the scene geometry, the application of LOD approaches is unproblematic. Further, the application of more complex projections is easy to integrate.

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Furthermore, the multiǦpass cube map texture creation of the imageǦbased approach provides an implicit fallǦback solution for older hardware. Discussion

The comparison shows that both approaches are capable of rendering stereographic nonǦplanar projections. The GBA is predominant over IBA in the range of functionality with respects to stereo rendering, the quality of the output images, as well as the rendering performance. The IBA has advantages considering the constant space complexity and its implementation. A disadvantage of both rendering techniques is the limitation to polygonal scenes only. They cannot be applied directly to volume rendering without major changes. Following to these results, we consider the GBA more suitable for stereo rendering of nonǦplanar projections than the IBA. According to our performance measurements, both approaches achieve satisfying results for virtual 3D scenes of the medium complexity of 500,000 triangles. For a scene complexity above this threshold, consumer graphics hardware seems not suitable for stereo visualization.

3 Application Examples

3.1 Active Stereo Rendering FrameǦsequential, active stereo can be achieved by using shutter glasses that are synchronized with the graphics hardware. Here, alternate left and right images are displayed on the screen, multiplexed in time. The user wears LCD shutter glasses which alternately show and hide the left right views. Active stereo can be implemented using OpenGL and a quad buffer (Haines, AkenineǦMöller 2002). This feature requires a professional graphics card with hardware stereo support. Similar to polarized rendering, it requires the evaluation of the projection function twice.


Fig. 7: Examples for anaglyph stereoscopic non-planar projections. A: rendering of a horizontal cylinder projection. B: A spherical projection with a field-of-view of 180°. (colour version on CD-ROM)

3.2 Passive Stereo Rendering Passive stereo viewing is independent of the refresh rates of the output device and can be achieved by using mainly two methods: anaglyph (Fig. 7) or polarized rendering. Anaglyph images provide a stereoscopic 3D effect when viewed with two coloured glasses, each with a chromatically opposite colour (usually red and cyan). The picture contains two differently filtered colour images, one for each eye. This can be implemented by computing two projections and performing a fullǦscreen compositing pass. The imageǦbased approach can be optimized by calculating only a single projection and perform texture sampling from the left and right raster representations. Thus, there is no need to generate stereo pairs. Older anaglyph glasses may introduce problems with reproducing correct colours. Our implementation supports the conversion to gray scale stereo pairs before compositing and the application of a colour optimization scheme as described in (Zhang, McAllister 2006). Another possibility is the use of polarized screens or projector filters in combination with polarized glasses. For the IBA, this approach requires the generation of two projections for the respective buffers. 3.3 ChromaDepth Stereoscopy

Chromo stereoscopy (Steenblik 1987), or colour stereoscopy, is a three dimensional viewing approach that does not rely entirely on binocular parallax and convergence. This chromaǦdepth technology is an inexpensive

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way to achieve a 3D impression of images that is compatible across different media such as paper or monitor displays. The user needs to wear a chromaǦdepth glass that performs a colour shift for oneǦeye. Unlike anaglyph or polarized stereo viewing approaches, the depth perception using chromaǦdepth glasses relies on colour coding the scene with respect to the current camera settings (Fig. 8). A mapping from the coordinates of a scene point V =(x, y, z) to a normalized colour value Cout of the respective chromaǦpalette has to be computed. The structure of such a function depends on the representation of the colour palette and the mapping of the point coordinates into a palette index. Similar to (Baily, Clark 1998), we represent colour table as 1D texture map. This enables the flexibility to change the colour models, e.g., red-green-blue (RGB), redǦwhiteǦblue (RWB), or cyanǦmagentaǦyellow (CMY), during runtime. Standardized colour tables can be obtained from the respective vendors of the chromaǦglasses.

Fig. 8: Examples for chroma-depth stereoscopy: A: A CMY chroma-depth rendering of a horizontal cylinder projection with 360° degree horizontal and 90° vertical field of view. B: A RGB chroma-depth rendering of standard planar projection with 60° field-of-view. (colour version on CD-ROM)

Fig. 9 shows an overview of the components and participating functions of the colour mapping. Given a colour Cin obtained by shading and texturing the input scene, the colour palette P as 1D texture, a mixing scalar m, and the eyeǦspace coordinates of a point V, the output colour is obtained by Cout = fmap(V, P, m) = flerp(Cin, fadjust ( fsample(P, T), m)). The sampling function fsample performs a texture lookǦup in P using the generated texture coordinates T. flerp function performs a linear interpolation between Cin and CC with respect to m. The texture coordinates are obtained by the concatenation of the following 1D functions: T = frm( fclamp, fdt (V)).


Fig. 9: Components and functions for the chromaǦdepth colour mapping. (colour version on CD-ROM)

The distanceǦtransform function fdt returns a linear scalar that is clamped and reǦnormalized using fclamp, and finally reǦmapped by frm. We can parameterize the distance transfer function with respect to the projection that is used. For a standard planar projection, the output equals the value of the z coordinate of V in eye space. For imageǦbased nonǦplanar projections, we set z = |V0 Ǧ V |, i.e., the distance of V to the camera position V0 (Fig. 10).

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Fig. 10: Comparison of corrected (bottom row) and original (top row) depth values, required to create chroma-depth stereo images using the image-based approach for creating non-planar projections. The line shows the distance between the center of projection of a virtual camera and a single depth complexity. (colour version on CD-ROM)

4 Conclusions This paper presents an overview for creating stereo renderings of nonǦplanar projections with image-based and geometryǦbased rendering techniques. In particular, it describes the implementation of a single pass imageǦbased rendering technique as an extension to an existing framework. Further, we describe application examples of stereoscopic rendering to 3D geovirtual environments. Furthermore, we present a comparison between geometryǦbased and imageǦbased approaches for generating stereo pairs with respect to four different criteria. This comparison shows that both approaches are capable of rendering stereographic nonǦplanar projections. The GBA is predominant over IBA in the range of functionality with respects to stereo rendering, the quality of the output images, as well as the rendering performance. The IBA has advantages considering the constant space and low implementation complexity. A disadvantage of both rendering techniques is the limitation to polygonal scenes only. They cannot be applied directly to volume rendering without major changes. Following to these results, we consider the GBA more suitable for stereo rendering of nonǦplanar projections than the IBA. According to our


performance measurements, both approaches achieve satisfying results for 3D scenes of the medium complexity.

References Baily, M.; Clark, D. (1998) Using ChromaDepth to obtain inexpensive singleǦimage stereovision for scientific visualization. In Journal on Graphic Tools 3, 3 (1998), 1–9. Bimber, O., Wetzstein, G., Emmerling, A., and Nitschke, C. (2005). Enabling viewǦdependent stereoscopic projection in real environments. In ISMAR ’05: Proceedings of the 4th IEEE/ACM International Symposium on Mixed and Augmented Reality, pages 14–23,Washington, DC, USA. IEEE Computer Society. Blythe, D. (2006). The Direct3D 10 System. In SIGGRAPH ’06: ACM SIGGRAPH 2006 Papers, pages 724–734, New York, NY, USA. ACM Press. Boubekeur, T. and Schlick, C. (2008). A Flexible Kernel for Adaptive Mesh Refinement on GPU. In Computer Graphics Forum, 27(1):102–114. Bourke, P. D. and Morse, P. (2007). Stereoscopy, theory and practice. Workshop, In VSMM 2007, Brisbane. Haines, E. and AkenineǦMöller, T. (2002). RealǦTime Rendering. AK Peters, Ltd., 2nd edition. Hou, X.; Wei, L.ǦY.; Shum, H.ǦY.; and Guo, B. (2006). RealǦtime MultiǦPerspective Rendering on Graphics Hardware. In EUROGRAPHICS Symposium on Rendering. Blackwell Publishing. Kolbe T. H. (2009). Representing and Exchanging 3D City Models with CityGML 3rd International Workshop on 3D GeoǦInformation, 13.Ǧ14. November 2008, Seoul, South Korea. in Lee, Zlatanova (eds.): 3D GeoǦInformation Sciences, Springer, 2009 Lorenz, H.; Döllner, J. (2008). Dynamic Mesh Refinement on GPU using Geometry Shaders In 16th International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision 2008, February 2008 Lorenz, H.; Döllner, J. (2009) RealǦtime Piecewise Perspective Projections, In GRAPP 2009 Ǧ 4th International Conference on Computer Graphics Theory and Applications, INSTICC Press, pages 147Ǧ155, February 2009. Peleg, S.; BenǦEzra, M.; and Pritch, Y. (2001). Omnistereo: Panoramic Stereo Imaging. In IEEE Transactions on Pattern Analysis and Machine Intelligence, 23(3):279–290. Spindler, M.; Bubke, M.; Germer, T.; and Strothotte, T. (2006). Camera Textures. In Proceedings of the 4th GRAPHITE, pages 295–302. ACM. Steenblik R. A. (1987): The chromostereoscopic process: a novel single image stereoscopic process. In SPIE: True ThreeǦDimensional Imaging Techniques and Display Technologies, January 1987. Tatarchuk, N. (2007). RealǦTime Tessellation on GPU. In Course 28: Advanced RealǦTime Rendering in 3D Graphics and Games. ACM SIGGRAPH 2007.

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Trapp M., and Döllner, J. (2008). A Generalization Approach for 3D Viewing Deformations of SingleǦCenter Projections, In GRAPP 2008 Ǧ International Conference on Computer Graphics Theory and Applications, INSTICC Press, Number 3, pages 162ǦǦ170, January 2008 Yang, Y.; Chen, J. X.; and Beheshti, M. (2005) Nonlinear Perspective Projections and Magic Lenses: 3D View Deformation. In IEEE Computer Graphics and Applications, pages 76–84. Zhang, Z. and McAllister, D. F. (2006). A Uniform Metric for Anaglyph Calculation. In Proceedings Electronic Imaging, San Jose, CA.

Section 9: Topographing and Thematic Geovisualization Go True 3D

3D Representation of Retreating Glaciers: Anaglyphs and the Geowall Wheate, R. and Menounos, B.

High-resolution mapping and visualization of a climbing wall Kolecka, N.

TOPGIS - swisstopo’s Production System for 3D Topographic Databases Suter, M.

Temple complex ‘Virtual Nako’ – 3D Visualisation of cultural heritage in Google Earth Nausner, B.

Challenges and Perspectives for True–3D in Car Navigation Götzelmann, T. and Katzer, J.

Holographic Relief Map Production by Using Topographic Line Maps Dalkiran, H. P., Özağaç, S., Büyükbayrak, H.

3D Representation of Retreating Glaciers: Anaglyphs and the Geowall

Roger Wheate, Brian Menounos Natural Resources and Environmental Studies Institute, University of Northern British Columbia, Prince George, BC, Canada

Abstract The Western Canadian Cryospheric Network (WC2N), which is funded by the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), 2005-2010, has collected glacier extents and digital terrain models of glacier areas dating from 1905-2005. These cover the two western provinces of British Columbia and Alberta and are being used to map glacier change, for glacier monitoring and future prediction. Data sources range from early (~1925) topographic maps, to post-1950 federal and provincial mapping programs and to early 21st century terrain models from remote sensing platforms that include the SRTM (Shuttle Radar Topographic Mission), ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) and SPOT (Système Pour l'Observation de la Terre). Traditional methods for displaying these surfaces include contouring, hillshading and oblique draped perspectives. These often involve challenges in effective representation, for example in distinguishing between smoother surfaces in accumulation snowfields with saturated contrast, and steeper slopes usually downvalley. We are now investigating presentation methods for the visualization of multiple extents and surfaces incorporating 3D technology, as part of our funding mandate to provide public education and outreach. In addition to traditional perspective views, anaglyph images are being increasingly used to represent surface elevations and changes. These can be generated M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_21, © Springer-Verlag Berlin Heidelberg 2012

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from standard commercial GIS and remote sensing software; some are also available on the internet through the British Columbia MapPlace website. We also use the University’s High Performance Computing Lab GeoWall, a low-cost polarization-based dual-projector interactive 3D stereoscopic system to generate large format perspectives and animation sequences. Two GeoWall visualization systems comprise a stationary, rear projection system and a more portable, front projection system. These enable visualization of glacier environments using a combination of digital terrain models and draped satellite imagery along with cartographic education. Keywords: Anaglyphs, alpine glaciers, ASTER, digital elevation models, GeoWall

1 Introduction The Western Canadian Cryospheric Network (WC2N) has collected multiple glacier extents and digital terrain models of glacier areas for western Canada - the provinces of Alberta (AB) and British Columbia (BC), dating from 1890-2010. These are being used to map glacier change, for glacier monitoring and future prediction. Data sources range from early topographic maps, post-1950 federal and provincial mapping programmes and early 21st century terrain models from remote sensing platforms that include the SRTM (Shuttle Radar Topographic Mission), ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) and SPOT (Système Pour l'Observation de la Terre). Traditional methods for displaying these surfaces include contours, shaded relief (hillshading) and oblique draped perspectives. We are now investigating presentation methods for the visualisation of multiple extents and surfaces incorporating true 3D technology, as part of our funding mandate to provide public education and outreach. In addition to traditional perspective views, anaglyph images are being increasingly used to represent surface elevations and changes. These can be generated using standard commercial GIS and remote sensing software; some are also available on the internet through the government of British Columbia MapPlace website (http://www.mapplace.ca). We also use the University’s High Performance Computing Lab GeoWall, a low-cost polarisation-based dual-projector interactive 3D stereoscopic system to generate large format perspectives and animation


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sequences. Two GeoWall visualisation systems comprise a stationary, rear projection system and a more portable, front projection system. These enable visualisation of glacier environments using a combination of digital terrain models and draped satellite imagery, and incorporate elements of cartographic education. Despite the fact that anaglyph representations cannot be considered truly three-dimensional (auto-stereoscopic) high-quality visualisations, they shall also be treated in the context of this book, due to the fact that anaglyphs are easy to generate using freeware (e.g. Beispiele für ANAGLYPH maker) and that anaglyph glasses are readily available in most offices dealing with geovisualisation.

2 Data sources Topographic image data consisting of maps, aerial and satellite imagery, and elevation models have been extracted from a variety of sources as listed below in Table 1.

Table 1: List of data for glaciers in western Canada Map vectors and elevations Historic alpine maps

1890-1940

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National Topographic maps and data Glacier maps- Int. Hydrological Decade BC and AB provincial data

1945-85 1965-75 1981-89

Image and elevations Stereo aerial photography ASTER SPOT HRS

1945 -> present 2000 -> present 2002 -> present

Images only Landsat TM / ETM+

1982 -> present

Elevations only SRTM (Shuttle Radar) LiDAR

2000 2006, 2007

3 Anaglyphs Anaglyphs require a pair of stereoscopic images, viewed through chromatically opposite glass lenses, usually red (for the left eye) and cyan. They were developed as early as 1853 to generate 3D images of pictorial photographs, and approximately a century later with aerial photographs. After some use with 3D films in the 1950s, they have experienced recent new popularity in the new millennium, and also with satellite imagery, both of terrestrial sites and other planets e.g. Mars. Most recently, Google Street View has implemented an analgyph option for 3D viewing. Anaglyphs have been shown to be useful tools in geomorphic interpretation (Abdallah 2007, Styles 1988). They can be created by combining two images or photos of the same scene taken from different locations, from a single digital elevation model (DEM) as in Fig. 1, or from a single view and a DEM, which can be used to simulate a second view. Red-Cyan anaglyph images can be produced by a variety of software: Geographic Information Systems, Image Processing, DEM and general graphics packages, both as commercial systems e.g. Adobe Illustrator and some freely downloadable e.g. AnaMaker, thus avoiding the need to purchase specialist software. Standard anaglyph viewing incorporates stereoscopic images in red and cyan, which when visually merged produce a 3D monochrome image. The ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite sensor is unusual in that it captures overhead (nadir)


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multispectral imagery ranging from visible to thermal infrared wavelengths, and an additional infrared band from an advanced position looking backward, to both automatically generate a DEM and enable stereo viewing (Fig. 2). Digital technology has enabled dynamic zooming and panning, beyond the simple magnification possible with hardcopy images by adding different viewing lenses (Fig. 3). In addition to displaying stereo pair satellite images or raster DEMs (as in Fig.s 1-3), it is possible to create anaglyphs using vector data such as contour lines and generated in GIS software. This is shown in Fig. 4 for the topographic area displayed in Fig.s 2 and 3, though from a different azimuth. Further layers could be added such as glacier extents and vegetation boundaries provided that they 3D features, that is, they are related to elevation values. It is also possible to represent colour in anaglyphs. The Province of British Columbia Ministry of Energy, Mines and Petroleum Resources has made available ASTER scenes, designed for the geology community through its Image Analysis Toolbox, with over 100 anaglyph images on their website at http://www.mapplace.ca. In order to enhance the standard monochromatic display, the backward looking image was left grey and was not orthorectified. The vertical image (bands 1,2,3) was orthorectified and combined into the anaglyph image; colours were designed to maximise geological contrasts (Fig. 5). However this extra realism is offset by reduced clarity away from the image centre. In addition to anaglyph images, the website includes stereo pair ASTER images available for download to view with a standard stereoscope. The nadir image has been orthorectified while the back-looking image has been left in its original state (Kilby and Kilby, 2006).

4 Geowall Geowall systems utilize dual DLP projectors and polarised light to create a passive full colour stereoscopic system which gives the illusion of 3 dimensions on a 2 dimensional screen. The term Geowall is derived from its application to visualize geology and the wall size potential of the display (Slocum et al., 2007). These systems are widely used to augment teaching in earth sciences and are further promoted by the GeoWall Consortium (http://www.geowall.org). Kelly and Riggs (2006) describe its effectiveness in enhancing students’ performance in introductory field mapping and expanding spatial skills. Our system at UNBC uses a 100 x 75 inch screen (approximately 2.5 x 1.9 metres) producing a high

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resolution projection to allow groups of researchers or students to view data sets at the same time. Specialised software is not needed as 3D images can be created with current versions of GIS and image processing packages (Davis 2004a, 2004b). In our case, we have utilised ESRI’s ArcScene and PCI’s FLY! to generate 3D images. The polarised images viewed on the GeoWall cannot be properly reproduced here but one is illustrated as a 3D perspective of a Landsat Thematic Mapper scene, incorporating local glaciers in the Cariboo Mountains of central British Columbia(Fig. 6). A parallel anaglyph version with earlier glacier extents overlain is displayed in Fig. 7, as an option that can be produced from both of the software systems listed above.

Footnote

The Challenger map (British Columbia) Prior to the digital era, George Challenger and his family assembled between 1947-54, a giant 3D map of the Province of British Columbia, carved into 196 panels of wood. It measures 80 x 76 feet (25 x 24 metres) and is listed by the Guinness Book of Records as the largest map of its kind in the world. Details can be found at: http://www.challengermap.org

Acknowledgements This work is part of the Western Canadian Cryospheric Network (WC2N), funded by the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS).

References Abdallah, C., Chorowicz, J., Bou Kheir, R., Dhont, D., 2007. Comparative use of processed satellite images in remote sensing of mass movements: Lebanon as a case study. International Journal for Remote Sensing, 28(19): 1-20. Davis, B. 2004a. Affordable system for viewing spatial data in stereo. ArcUser, July-September, 48-49. http://www.esri.com/news/arcuser/0704/files/geowall.pdf Davis, B. 2004b. Virtual reality meets GIS: 3-D on the wall. ArcNews, summer. http://www.esri.com/news/arcnews/summer04articles/virtual-reality.html Kelly, M.M. and Riggs, N.R. 2006. Use of a virtual environment in the Geowall to increase student confidence and performance during field mapping: an


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example from an introductory-level field class. Journal of Geoscience Education, 54, 2, March, 158-164. Kilby W, and Kilby C 2006. ASTER Imagery for British Columbia – An Online Exploration Resource. BC Ministry of Energy, Mines and Petroleum Resources internet website: http://www.em.gov.bc.ca/Mining/Geolsurv/Publications/catalog/ Slocum, T.A., Dunbar, M.D., and Egbert, S.L. 2007. Evaluating the Potential of the GeoWall for Geographic Education. Journal of Geography, 106, 3, 91 – 102 Styles, P.J. 1988. The production of anaglyphs. Geoscience and Remote Sensing Symposium, IGARSS '88. Remote Sensing: Moving Toward the 21st Century; 1, 485 - 487

High-resolution mapping and visualization of a climbing wall

Natalia Kolecka Department of GIS, Cartography and Remote Sensing, Institute of Geography and Spatial Management, Jagiellonian University, Krakow, Poland

Abstract Many cartographers are making an effort to depict mountainous steep relief on classical maps. There are many techniques that enable achieving this goal effectively. However nowadays we notice a trend toward 3D realistic representation of relief, using Digital Elevation Models (DEMs) derived from aerial photographs or satellite imagery. They are very useful and sufficient for visualizing and modeling various terrain features – from flat to hilly. Nevertheless the mountainous terrain is very problematic, as very steep slopes cannot be seen and depicted from bird’s eye view. That is why an alternative method should be used to gather information and visualize terrain with vertical relief, otherwise information about such areas is omitted or very poor (Butler et al. 1998; Gooch et al. 1999; Buchroithner 2002; Mergili 2007). The paper presents a possible application of close-range photogrammetry for mapping and visualization of steep (close to vertical) rock walls. In this way integration of photogrammetry, digital cartography and photorealism meets the needs of information systems for climbers and tourism in general. Technology and software is similar to that being used in aerial photogrammetry, but some differences in concept should be considered in order to generate spatial model in horizontal projection, so called quasi-DEM. The research object is a part of natural climbing wall M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_22, © Springer-Verlag Berlin Heidelberg 2012

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situated in Krakow, Poland. The surface is approximately vertical, with some parts which are overhung. It is also very rough, so many shades appear. For the creation of quasi-DEM, quasi-orthophoto and virtual rock face, 4 overlapping photographs were taken with Nikon D80 amateur digital camera. Object distance was about 5.5 m, and ground resolution about 1.8 mm. The camera was previously calibrated with ImageMaster software by Topcon and known parameters of the camera lens allowed the removal of the distortion from the images. ERDAS LPS (Leica Photogrammetry Suite) was used to perform photogrammetric processing. In order to demonstrate the potential of the technique, some steps used by climbers are marked, and anaglyphic methods facilitate a three dimensional perception. That can help inexperienced climbers to plan their route and prepare for the real experience. Keywords: close-range photogrammetry, visualization, anaglyph, vertical relief, terrain models, mountain cartography, climbing

1 Introduction Many cartographers are making effort to depict mountainous steep relief on classical maps. There are many techniques that enable achieving this goal effectively. However nowadays we notice a trend to more realistic modeling and visualizing various terrain features using 3D representation of relief. It is achieved using Digital Elevation Models (DEMs) derived from aerial photographs or satellite imagery. They are very useful and sufficient for flat or hilly terrain, nevertheless when it comes to mountainous terrain, many problems occur. When we cope with steep slopes or almost vertical rock faces it is impossible to depict them precisely from the bird’s eye view. It is a case of vertical (or near-vertical) aerial photographs, that are very popular source of elevation data. Since they are taken in a central projection, some parts of terrain can be invisible or seen in short. In this way information about such areas is omitted or very poor, and the precision of the data sometimes is not sufficient for highresolution mapping of small areas (Butler et al. 1998; Gooch et al. 1999; Mergili 2007). A similar problem is connected with satellite imagery. Another possibility is the airborne laser scanning, that gives a spatial resolution of about 1m, still with a cost of equipment and personnel exceeding capabilities of a typical low-budget project. That is why the need for alternative methods to gather information and visualize terrain with vertical and steep relief is urgent.


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Mapping rock faces should be the most effective if imagery is taken when the camera viewing direction is (near) perpendicular to the surface. For that reason implementing of close-range photogrammetry was regarded adequate to use for vertical relief mapping. However differences in concepts should be considered in order to generate spatial model in horizontal projection, so called quasi-DEM, followed by quasi-orthophoto. Some previous works connected with DEM generation from close-range photogrammetry are for example: creating virtual Eiger North Face (Buchroithner 2002), acquiring accurate information from a natural gravel bed river (Butler et al. 1998) and a mountain slope (Mergili 2007), documentation and modeling of an archeological site (Haggren et al. 2005), change detection of glacier (Pitkaenen and Kajuutti 2004), mountain slope (Landstaedter and Kaufmann 2004) and river chanel (Chandler 2001), monitoring of landslides (Cardenal et al., 2008). There is a very wide spectrum of application of this method, and good results can be achieved.

Fig. 1. Location of the study area (http://maps.google.pl/)

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The aim of this research was to generate an accurate 3D model of a climbing wall using imagery taken with non-metric digital camera and Ground Control Points (GCPs) from GPS survey, presenting a possible application of close-range photogrammetry for mapping and visualization of steep (close to vertical) rock walls. In this way integration of photogrammetry, digital cartography and photorealism meets the needs of information systems for climbers and tourism in general. The research object is a part of a anthropogenic limestone climbing wall (former limestone quarry) situated in Kraków, Poland (Fig.1). The whole object is a traverse about 4 m high and 100 m long. On the traditional orthophoto the object is seen only as a white line (see an arrow on the Fig.1 ). Maximal differences of depth in this wall do not exceed 60 cm, but the surface is very rough and irregular. The wall is approximately vertical, but some parts are overhanging. For the research a varied section of the wall was chosen, about 6 m long.

2 Input data All needed input data were acquired during field work in December 2009 and consisted of photogrammetric and GPS survey data. Moderate weather conditions were favorable, as clouds receded to avoid sharp shadows on the object. In every single case the general concept of close-range photogrammetry is the same, however details vary. They depend on object of interest, required accuracy of survey or mapping, used equipment and software for further proceedings. 2.1 Terrestrial imagery A digital non-metric camera Nikon D80 with 10.2 million effective pixels matrix with sensor size 23.6 x 15.8 mm was used in the study. The camera was equipped with Nikon AF 20mm 1:2.8 lens. The lens was set to 6m and taped to avoid changes in the camera internal geometry while conducting the field work. The kit had been previously calibrated using Topcon ImageMaster (Previously PI-3000) PI-Camera Calibration Software. During the calibration process the parameters were set: focal length, principal point, four distortion parameters and resolution. It is an important step in 3D modeling and measurements, as it helps in achieving better accuracy. For preserving stable camera position while photo shooting the camera was mounted on a tripod and a remote trigger was used. Object distance was about 5.5m that gives approximate terrain pixel size of


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1.8mm. Four photographs were taken in one strip with an overlap ranging from 40 to 55%; the base had length of about 2m. 2.2 Ground Control Points (GCPs) 9 GCPs were measured with Leica GPS1200 receiver GX1230 GG and antenna Leica AX1202 GG. Its nominal real time survey accuracy is higher than 1cm. The GCPs were marks glued to GPS poles, what enabled simultaneous photogrammetric and GPS survey. The poles were situated in overlap, so each of them could have been measured on two photographs. Also the approximate coordinates of camera positions were measured as initial values for image block forming. The coordinates were in Polish National Coordinate System “2000”. Position and height quality of GCPs was maximally 3.4mm.

Fig. 2. Study area: climbing wall, Krakow, Poland. (colour version on CD-ROM)

2.3 Coordinate system While working with terrestrial images some problems occur. LPS software is able to generate DEM and orthoimage only from the aerial photos, when x,y-plane is approximately parallel to the image plane. The second problem is that in overhanging terrain some x,y-coordinates may have more than one z-coordinate. Therefore a local coordinate system (LCS) was defined. Reference plane X’Y’ was set with the least square error method, using 9 GCPs, and Z’-axis was perpendicular to the plane. The origin of the system was set in such a way, that the model had only positive and not very big values.

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GCPs Y’

LCS Z

X’

Z’ Reference plane Y

GCS

Camera station X

Fig. 3. The schema of local coordinate system (X’Y’Z’).

The spatial 3D transformation was applied to all GCPs and camera positions. Also thickness of poles (radius 15 mm) was taken into account and after transformation the GCPs z-coordinates were increased by 15 mm.

3 Data processing Schema of data processing is shown below. The basic steps consisted of preprocessing the input data (this means images calibration and transforming GCP coordinates to the Local Coordinate System), setting up the LPS project, performing the photogrammetric process of orientations and triangulation and generating the quasi-DEM and quasi-orthophoto, that were then used for visualization.

High-resolution mapping and visualization of a climbing wall INPUT TERRESTRIAL DIGITAL IMAGERY

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CAMERA CALIBRATION PARAMETERS

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APPROXIM ATE EXTERIOR ORIENTATION

COORDINATE SYSTEM DEFINITION

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Fig. 4. Schema of data processing

3.1 Image calibration First the Topcon ImageMaster Software was employed for image calibration, according to cmr-file from the camera calibration. Basing on the file, the software automatically creates calibrated images having the same size and resolution as input ones. They can be used for further modeling without need to give details of the lens distortions and principal point while working in digital photogrammetric workstation – except of focal length and pixel size. 3.2 Stereo model generation To generate the stereo model, quasi-DEM and quasi-orthophotos digital photogrammetric workstation (DPW) Leica Photogrammetry Suite 8.7 (LPS) was used. It was available for the project in 30-day one-time-only version from ERDAS. LPS enables automated processes, that increase productivity and ensures high accuracy. To create the stereo model several steps were performed. First a model was set up by defining the camera type, reference coordinate system and framespecific information. Then the image pyramids were created for faster operating on images. Also giving a sensor definition and interior orientation parameters according to the calibration file was necessary – only focal length (19.8 mm) and pixel size in x and y direction (5.9 m) was needed (as the images had been calibrated previously and lens distortion and principal point is now equal to 0). This part was followed by

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defining the exterior orientation parameters – coordinates of the perspective centers and rotation angles. Rough approximate values were given as the first inputs with initial status. 9 GCPs as full control points and a few tie points were then measured manually. On the base of this measurements coordinates of the perspective centers were computed. The final step was the relative orientation and triangulation, performed on the base of automatically generated tie points. The computed coordinates were set fixed and tie points were automatically generated for the whole block of four photographs. The algorithm used adaptive strategy crosscorrelation with feature-based matching (ERDAS, LPS Product Description). Default values of its parameters gave good results, as it could have been stated after manual revision of generated points. In this work 41 tie points was manually measured (Fig.5).

Fig. 5. Tie points distribution on the oriented images

The relative orientation was performed on the base of the tie points – as a stable point the position number 22 was chosen and given fixed status. Other parameters were allowed to flow, so were given status initial. Also the X coordinates were set to fixed for all the perspective centers. The triangulation was performed and results appeared. A few values in the triangulation summary and report need to be checked: total image unit weight RMSE, iteration convergence and the exterior orientation parameters. If the results are satisfactory, they can be accepted. 3.3 Digital Relief Model extraction As soon as the model was set, a digital relief model could be extracted. The height accuracy was about 0.2 ‰ of the “flying” height. Respectively to object distance about 5.5 m, the accuracy should be about 0.01 m.


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Differences in depth of the wall surface slightly exceed 0.5 m. In comparison to the object distance, the depth gives over 10% of the distance, and that corresponds to the aerial case of hilly or mountainous areas. The Leica Photogrammetry Suite enables changing parameters of relief extraction depending on an object characteristics. All predefined sets of parameters were tested in order to achieve the best results. The relief model had the highest accuracy when created with Default settings, using other settings the amount of points located incorrectly was increasing. Quasi-DEM was generated as a single file (728 columns, 242 rows), containing values from 51.832 m to 52.398 m (LCS). Also information about DEM quality was generated as individual raster file. About 78% of points were of excellent and good quality, 19% were fair and isolated, and more than 2% were suspicious. Final pixel size was set to 0.01 m.

Fig. 6. DEM quality (colour version on CD-ROM)

3.4 Quasi-orthophotos generation To achieve the objective of this work, that means realistic visualization, a good texture is needed for draping over the relief model. The texture that naturally should be used is a well adjusted quasi-orthophoto. After relief model extraction, quasi-orthophotos were generated on the base of the model. Pixel size was set to 0.005m. Some distortions could be seen, especially in the places where relief model was not very accurate. Nevertheless it is sufficient for the purposes of realistic visualization.

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Fig. 7. Quasi-orthophoto created from photo 23.

4 Results

4.1 Anaglyph visualization As soon as triangulation results are accepted and exterior orientation parameters are updated the stereo model of the climbing wall can be observed in anaglyph (Fig.8). It can be calculated in LPS. But it is also possible to use more common graphic programs for that purpose. Only red-blue or red-green glasses are required to observe 3D space on a standard map format – on the screen or on the plot.


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Fig. 8. Anaglyph visualization of the climbing wall in the horizontal view. (colour version on CD-ROM)

Even if the accuracy of the triangulation and relief model generation was not perfect, the effects of the anaglyph visualization is good. Even very small stones and holes can be seen. The exaggeration of the depth of the model increase the effect of perceiving the wall in 3D. 4.2 Virtual 3d visualization A relief model and a suitable image texture was used to create virtual model of the object (Fig.9), providing free navigation in the space. Such a textured model can be exported to VRML format and shared with potentially interested users, as many free VRML-viewer software are available online. Also animations were created and saved as films, that can be provided for broad community.

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Fig. 9. Virtual model of the climbing wall seen in 3D.

5 Further development In this work a small climbing wall and its high-resolution mapping were used to explore the capabilities of existing technologies. However in the future it is supposed to use the technology for bigger rock walls and highmountainous areas, such as Tatra Mountains in Carpathians. Obviously those relief models will be in lower resolution, but still the information about relief should be more accurate than derived from aerial sensors. An important issue is also to develop a method to integrate the “terrestrial” and “aerial” data. One of crucial problems is their different resolution and coordinate systems. Second one – data redundancy from the GIS point of view. In mountainous terrain are overhangs, where for one XY-coordinate at least two Z-values exist. In this context the question of different data models (such as TIN and point clouds) should be considered. Also terrestrial laser scanning seems to be crucial as it becomes more popular and accessible nowadays. It allows gathering spatial data of very high resolution, even for distant objects. When digital camera images are provided, coloured point cloud can be created, what makes modeling and visualizing such data very powerful and efficient. Further applications comprehend also cartographic presentation of the areas of interest on traditional 2D maps and in a GIS database. The issue includes also presenting the data to the broad community, especially to tourists and climbers via Internet.


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6 Conclusion Crucial aspect in mapping very steep slopes is that they are hardly visible on classical 2-dimensional cartographic or GIS visualizations (see Fig.1). If very steep slopes are of interest they should be depicted in another way, using relief models and orthophotos produced with terrestrial sensors, that register data at approximately right angle to the object, within a local coordinate system. The reference plane (XY-plane) must be approximately parallel to the object surface, because Leica Photogrammetry Suite assumes that the reference plane is horizontal. One of the obstacles met was the inability to extract a digital relief model and to generate orthophotos of a global coordinate system for the vertical climbing wall. An unquestionable advantage of close-range photogrammetry is a high spatial resolution of mapped object, as images are taken from much shorter distance than in the aerial case. Terrain pixel size depends on the object distance and the camera focal length. Considering amateur digital cameras, especially reflex cameras, most of them are nowadays equipped with 8 or 10-million pixels CCD sensor. This can be used for mapping purposes if a sufficient number of photographs are taken. In this study terrain pixel size was about 1.8mm, that gives abilities to produce very high-resolution relief model of the object. It is also recommended to calibrate the camera to reduce image distortions. Special photogrammetric software enables creation of many different 2D or 3D presentations of processed object. The most obvious is quasiorthophoto, created in projection on a vertical reference plain. This method presents the climbing wall well, but gives no detailed information about the exact shape of it. For that reason different methods of 3D viewing (e.g., anaglyphs) seem to be better, more suitable and easier to understand for an unskilled person (Murphy 2004). The undoubted advantage of anaglyphs is the low cost, as the only equipment needed are red-blue or red-green glasses. Besides, it can be used with all kinds of media and presented to broad society through World Wide Web (Doneus 1999). In addition to anaglyphs a virtual 3D visualization is a reasonable alternative, as a user can freely manipulate the view. Nevertheless in such a case a computer is necessary for 3D-viewing. That can limit its range of use, especially in case of climbers where the portability of their maps seems to be crucial.

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References Buchroithner M (2002) Creating the virtual Eiger North Face. ISPRS Journal of Photogrammetry & Remote Sensing 57: 114-125. Butler JB, Lane SN, Chandler JH (1998) Assessment of DEM quality for characterizing surface roughness using close range digital photogrammetry. Photogrammetric Record, 16(92): 271-291. Chandler J, Ashmore P, Paola C, Gooch M, Varkaris F (2001) Monitoring river channel change using terrestrial oblique digital imagery and automated digital photogrammetry. Annals of the Association of American Geographers, 92(4): 631-644. Cardenal J, Mata E, Perez-Garcia JL, Delgado J, Hernandez MA, Gonzalez A, Diaz-de-Teran JR (2008) Close range digital photogrammetry techniques applied to landslide monitoring. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Beijing, China, Vol. XXXVII, Part B8: 235-240. Doneus M, Hanke K (1999) Anaglyph images – still a good way to look at 3Dobjects? http://cipa.icomos.org/fileadmin/papers/olinda/99c411.pdf (July 05, 2009) ERDAS, LPS Product Description. www.erdas.com. Gooch MJ, Chandler JH, Stojic M (1999) Accuracy assessment of Digital Elevation Models generated using Erdas Imagine Orthomax digital photogrammetric system. Photogrammetric Record, 16(93): 519-531. Haggren H, Koistinen K, Junnilainen H, Erving A (2005) Photogrammetric Documentation and Modelling of an Archeological Site: The Finnish Jabal Haroun Project . Proceedings of the ISPRS Working Group V/4 Workshop 3D-ARCH 2005: "Virtual Reconstruction and Visualization of Complex Architectures" Mestre-Venice, Italy. Landstaedter R, Kaufmann V (2004) Change detection of a mountain slope by means of ground-based photogrammetry: a case study in the Austrian Alps. Proceedings of the 4thICA Mountain Cartography Workshop, Vall de Nuria, Catalonia, Spain, Monografies tècniques 8, Institut Cartogràfic de Catalunya, Barcelona, pp 77-88. Mergili M (2007) Stereo matching of terrestrial digital photographs – an alternative for the generation of high-resolution DEMs in situations of poor data availability? Geospatial Crossroads @ GI_Forum (Car, A., Griesebner G. und Strob J. (eds.)), Proceedings of the First Geoinformatics Forum Salzburg 2007, Wichmann, Heidelberg, pp. 110-119. Murphy T (2004) Visualising and Learning about the environment with 3D maps. Proceedings of the 2004 Conference of North American Association for Environmental Education http://www.naaee.org/conference2006/2004conference-proceedings (July 05, 2009).


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Pitkaenen T, Kajuutti K (2004) Close-range photogrammetry as a tool in glacier change detection. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Istanbul, Turkey, Vol. XXXV, Part B7, pp. 769-773.

TOPGIS - swisstopo's Production System for 3D Topographic Databases

Martin Suter ESRI Schweiz AG, Zurich, Switzerland

Abstract To truly visualize topographic data in 3D requires truly 3D topographic databases. The Swiss Federal Office of Topography (swisstopo) is replacing their current map-based 2D VECTOR25 dataset with a 3D Topographic Landscape Model (TLM). This represents a major shift in their internal production workflow, and also a beneficial change for their customers who require accurate 3D geographical reference data. The TLM is swisstopo’s new vector landscape model. It will be very upto-date across all of Switzerland, seamless across this area, 3D, and very accurate with better than 1 meter accuracy in all three dimensions. The TLM forms the basis for several geo-data products and the Swiss National Map series. The TLM is accompanied by a new Digital Terrain Model (DTM) which is designed to be consistent at all times with the TLM. The DTM is derived principally from LIDAR (Light Detection and Ranging) data. For the capture and administration of the TLM and the DTM, a new high-performance infrastructure called Topographic Geographic Information System (TOPGIS) has been built for swisstopo by ESRI Switzerland. As the central production infastructure for the TLM, TOPGIS is a modern, database-centered system for data capture, editing, management and storage.


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The TLM and DTM are photogrammetrically updated based on high resolution digital imagery. TOPGIS supports three simultaneous modes for producing 3D data: x Stereo-photogrammetric 3D TLM production x Stereo-photogrammetric DTM production x TLM production by using mono-plotting from orthophotos and the DTM Keywords: ArcGIS, DEM/DTM, digital photogrammetry, GIS, Production, Stereoscopic, Three-dimensional, Topographic Landscape Model

1 The Need for Change Traditionally, the key task of national mapping agencies has been the production of the national map series, but in recent years the need for digital topographic base data has continued to increase. This data is not only used to produce printed paper maps, but also to create a variety of products including digital multimedia products, digital elevation models, and 3D city models. For swisstopo the increasing demand for better, more up-to-date, and more diverse digital data has meant that the generation and rapid updating of such products has taken on a high level of importance. To create a new generation of topographic data products, swisstopo has established a production infrastructure called TOPGIS (O’Sullivan et al. 2008). This system is used to create, manage and update the new Topographic Landscape Model of Switzerland (TLM), as well to update a corresponding LIDAR-based DTM. swisstopo’s previous vector landscape model product VECTOR25 was derived from their 1:25,000 map series. VECTOR25 is a seamless model consisting of about eight million objects with a positional accuracy of the map of three to eight meters. It was also limited to 2D. The new three dimensional TLM is much more accurate and precise than the previous model. Every feature of TLM is stored in a geodatabase with better than one-meter accuracy in all three dimensions. The TLM serves as the base landscape model for Switzerland’s Spatial Data Infrastructure (SDI), and it is a central dataset from which many products can be derived. Realizing TLM meant that a large part of the previous production flow needed to be reversed (see Fig. 1).


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Fig. 1. Reversing the production process with TLM.

The new workflow has a number of advantages. x Processes are streamlined The previous production lines were complex and involved connecting together several independent systems, as well as analogue steps. x Time-to-market is reduced The updating of TLM takes place over a shorter period of time (from “flying” the aerial photos to delivering products) and data are very current. Important layers such as roads and buildings are updated annually. x Accurate 3D model The 3rd dimension gathered during the photogrammetric stage is retained in the vector TLM. Leveraging these Z-values was previously not possible in the purely 2D VECTOR25 model.

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2 The Topographic Landscape Model

Fig. 2. A subset of a TOPGIS work-unit displaying TLM Data. (© 2009 swisstopo) (colour version on CD-ROM)

As the national base landscape model, the TLM is seamless and covers all of Switzerland. Once finished, it will consist of approximately twenty million objects. Its objects and their relations are stored in a geodatabase using an underlying commercial-off-the-shelf DBMS. Because objects are directly captured from high-resolution aerial imagery, TLM geometry is appropriate for product scales as large as 1:10,000. This compares favorably to an appropriate scale of 1:25,000 for the VECTOR25 product. TLM itself is not a product, but rather the basis for a variety of products. These include 1:25,000 cartographic data products, as well as printed and electronically-disseminated maps. Each vertex of each TLM object has X, Y and Z coordinates, which means that objects in the TLM should can (and should) stay consistent with the DTM. For example roads should be placed on the DTM. Therefore the DTM is designed to be compatible to and consistent with TLM. Originally captured by a LIDAR sensor, the DTM includes mass points and breaklines, and it is photogrammetrically updated in parallel to the updating of TLM. Finally, the TLM consists of ten thematic categories ranging from land cover to manmade objects (see Fig. 3).


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Fig. 3. TLM’s thematic contents. (© 2009 swisstopo)

3 Updating TLM: TOPGIS For capturing, updating, and administrating the TLM and DTM, ESRI Switzerland and five sub-constractors built a new production infrastructure for swisstopo called Topographic Geographic Information System (TOPGIS). TOPGIS is based entirely on ESRI ArcGIS, and it includes desktop, server, and mobile GIS components. Stereo photogrammetry is fully integrated through the Stereo Analyst Extension for ArcGIS (SAFA) from ERDAS. Custom development by ESRI Switzerland extends the standard software and implements the workflows and requirements specific to swisstopo. TOPGIS is designed to meet three key success factors related to data production. x Workflows need to be addressed because several delivery versions of TLM are worked on in parallel by up to fifty users.

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x Operator productivity and system performance are crucial. Compared to the previous VECTOR25 model the operators need to capture significantly more detailed data in a shorter amount of time. x The production of a primary 3D Model must be addressed. This means that each vertex of each object must have Z-values. The model must be designed to serve as the basis for a variety of products, not only for maps. Upon analysis of these requirements, it was determined that a seamless integration of a modern Geographic Information System (GIS) with digital photogrammetry is essential to meet these criteria. TOPGIS is such a marriage between GIS and digital photogrammetry. 3.1 3D Data Capture The third dimension of the TLM is captured either photogrammetrically based on high resolution ADS40 / ADS80 stereo imagery, or alternatively by mono-plotting using orthophotos and the DTM. To work in 3D stereo mode the operator first selects images from swisstopo’s aerial image database (LUBIS DB). Next, for fast display performance these images are copied to the local workstation. During this process, images receive their orientation from the LUBIS DB. Twenty inch planar stereo screens are used for stereo viewing (see Fig. 4). The polarized left eye lens of the glasses blocks light from the top monitor, while light from the lower monitor is blocked by the right eye lens. This technology allows flicker-free operation under any office’s ambient light. 3D stereo mode is used in the following situations: x To capture objects which “form or shape” the terrain such as waterways, roads, and railways x To edit the DTM x To capture the heights of objects such as roofs, electric poles, and bridges Although the TLM is 3D, not all objects are edited in stereo mode. This is because they “sit” on the terrain, and thus they assume their Z values from the underlying DTM. Some examples include hiking trails, land cover, and boundaries. In TOPGIS mono and stereo capture are seamlessly integrated. For example, the operator can begin capturing a road in stereo, and then where


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the ground becomes obscured (such as in a dense forest), he or she can continue by mono-plotting using a different image source (for example shaded terrain relief), returning to the stereo screen when the road emerges from the forest. To change modes, the operator simply moves the mouse cursor from the 3D screen to the 2D screen or vice versa. All objects are always visible on both screens. Rooftops are captured completely in stereo using an add-on to SAFA. Templates assist the operator to quickly collect these features, handling varying degrees of complexity. In addition to these pre-defined templates, manual construction and editing tools are provided for the creation or modification of any roof shape. To create a scene true to reality, roofs can be ‘extended to the ground’ or to an existing terrain, creating a 3D model that can be used in a visualization package. A complete set of point, breakline and area tools – including a tool for auto correlating new points - are provided for modifying the DTM in the stereo client. The terrain stored in the geodatabase is decomposed into points and breaklines with triangle and contour display. As the terrain is edited, contours are dynamically updated in the stereo window to assist in the visualization and interpretation of the terrain.

Fig. 4. A TOPGIS workstation with 2D and 3D display. (© 2009 swisstopo)

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3.2 Workflows Using the central GIS Database (called geodatabase) allows swisstopo to create and maintain multiple parallel release-cycles of the TLM. A releasecycle includes all operations, which are made with the focus of creating a release of TLM. Within each release-cycle the operators’ work is organized into work-units. Work-units define a perimeter within which a defined set of layers can be edited. Automated batch jobs reconcile the operators’ daily work with the release-cycle during night time. This helps to prevent uncontrolled growth of the database state lineage tree. During the reconcile step conflicts may be detected between the edits of different operators. For example a road object extending over more than one work-unit may have been edited by several users. The system will first try to automatically resolve conflicts. Only if automatic resolution is not possible the TOPGIS assigns the conflicts to a “work-list” that is subsequently checked and manually resolved by an administrator. Periodically during data collection and particularly when a release-cycle is completed a multi-level, rule-based quality assurance system ensures that a pre-defined level of quality is met. This modular, high-performance QA system was especially built for TOPGIS and it includes 3D tests. One step in the production chain of TLM is the completion in the field. The TLM data is improved and completed in the field using ruggedized handheld tablet PC’s and GPS receivers. The data is checked out from the central data base in the office and subsequently edited in the field. Because tablet PC’s are used, the full functionality of ArcGIS is available to the field topographer. The GUI only differs slightly from the office mono clients. 3.3 Productivity In order to minimize the number of mouse-clicks, mouse-movements and menu calls special tools and mechanisms were built. All relevant edit tools are available on a configurable toolbar for direct access. This toolbar can also be displayed as a pop-up menu at the current cursor position. A number of specialized tools were developed for example for automatically adjusting complex geometries to each other. As the user selects which object to capture next TOPGIS automatically sets all the edit-properties - e.g. snap settings, Z-capture rules, default attributes, etc. - based on the type of object behind the scenes. These settings are predefined by an administrator, stored in a Data Dictionary,


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and loaded automatically depending on the actual context. The operator can override the defaults if needed. The linear feature extraction tool is a semi-automated object collection tool that helps digitize objects from imagery more efficiently. It focuses on tracing line or polygon features, mostly roads, water bodies, vegetation, etc. The tool automatically extracts the object following the seed points given by the operator. A so called rule engine enforces a set of consistency rules at each edit operation helping the user to prevent errors while editing. The rule engine is designed in a way that the user is not distracted by any delay. As an example a specific rule supports the system’s behavior if the user splits a road segment. In this case the rule engine recognizes the split operation, assigns the existing unique ID to the longer part of the split segment, assigns a new unique ID to the shorter part, and assigns all existing relations such as road name or routes to both segments. Because TOPGIS integrates Desktop, Server, and Mobile GIS as well as digital photogrammetry there are no data conversion steps necessary to traverse system boundaries as it used to be with previous solutions. Conversion is only necessary when data from 3rd parties is imported (such as road authorities or National Mapping Agencies of neighbouring countries) or when products are exported for customers. A individually developed component called DataHub is used to do import- and export jobs. Such jobs may include format conversion as well as schema conversion. The DataHub is based on Safe Software’s FME (the Feature Manipulation Engine) combined with ArcGIS Server. The hardware and software infrastructure supporting the productivity of TOPGIS is designed for assuring short response times even with the high data volumes that are used. To assure availability a DBMS failover mechanism is used. Failover is the capability to switch over automatically to a redundant standby database.

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Fig. 5. A Screen Snapshot of the TOPGIS 2D screen. (© 2009 swisstopo) (colour version on CD-ROM)

4 Conclusion und Summary TOPGIS is a marriage between GIS and digital photogrammetry providing the infrastructure for the production of TLM and DTM. TOPGIS consists of ESRI’s ArcGIS software, ERDAS StereoAnalyst for ArcGIS, and FME Server, as well as custom developed modules to meet specific requirements of swisstopo’s workflows. With TOPGIS, swisstopo has a very modern infrastructure with a strong emphasis on productivity and workflows. TOPGIS enables swisstopo to efficiently produce an up-to-date, primary 3D data set designed to serve as the basis for a variety of products, not only for maps.

References O’Sullivan, L., Bovet, S., Streilein, A.: TLM – THE SWISS 3D TOPOGRAPHIC LANDSCAPE MODEL, The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008

Temple complex ‘Virtual Nako’ – 3D Visualisation of cultural heritage in Google Earth

Ben Nausner Department of Geography and Regional Research, University of Vienna, Vienna, Austria

Abstract The preservation of cultural heritage and the communication of its vital importance for modern society represent an increasing and demanding challenge for the scientific community. Due to the occurrence of cultural objects in geographic space and time, cartographers are questioned, amongst others, to deal with new forms of geo-visualisation. These new visualisations improve communication between scientists and a broad audience by facilitating a more efficient information exchange. A national research network gave the setting for cartographers at the University of Vienna to develop and implement a Google Earth 3D visualisation of a Buddhist temple complex built during the early second millennium. This paper describes the efforts of the national research network and the preceding research and preservation project, which led to a detailed conception for the digital reconstruction of the sacred temples in Nako, Himachal Pradesh, India. Furthermore the workflow from acquisition of basic datasets to their refinement for an interactive view in Google Earth is discussed. Finally an outlook on future developments towards a more immersive 3D visualisation on a virtual reality wall will be given. Keywords: Cultural Heritage, Western Himalaya, 3D Visualisation, Google Earth


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1 Introduction The national research network ‘The Cultural History of the Western Himalaya from the 8th Century’ (CHWH), financed by the Austrian Science Fund (FWF) was founded in 2007 at the University of Vienna. As part of this research network the Department of Geography and Regional Research has developed a map-based online information system for visualizing cultural history in the area of the western Himalayas. Within this Cultural History Information System (CHIS) special views form a complementary component of the comprehensive information architecture. Special views represent interactive applications that depict certain research objects relevant to the national research network in large-scale detailed visualisations using integrated-media techniques. The specific use of new media techniques is primarily intended to improve and investigate geo-communication processes in an interdisciplinary setup. The implementations vary according to the requirements and objectives of the special view, and form a substantial part of scientific research. Thus special views within the CHIS provide the possibility of a deeper examination and better understanding of selected research objects. (Kriz 2009) In the following the design and modelling processes of the special view ‘Virtual Nako’ for Google Earth will be described in detail. The focus is on outlining methods for the virtual reconstruction of the Buddhist temple complex and potential future developments for 3D visualisations of cultural heritage.

2 The Nako Research and Preservation Project (NRPP) Nako is a small village in the district Kinnaur in Himachal Pradesh, Northern India. Situated at about 3600m above sea level and surrounded by the impressive Himalayan mountain range the Buddhist temples of Nako give evidence of a particular cultural heritage and a former centre of Buddhism in the Western Himalaya. The complex is among the oldest foundations in this area and can be dated back to the early second millennium (11th to 12th century). (Luczanits 2003) Four temples and a number of associated structures occupy an area of about 1000 square meters, which gradually slopes from the eastern to the northern edge. Due to the imminent corrosion of the temples’ fabric and the precious wall paintings within, the villagers asked for help to restore and preserve the sacred temple complex. (Klimburg-Salter 2003)

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Since 1998 the University of Vienna and other institutions took charge of this problem and supported the local community via different channels. With the foundation of the Nako Preservation Project (later Nako Research and Preservation Project - NRPP), involving architects, painting conservation experts, art and religious historians and cultural anthropologists, the main rebuilding and conservation activities were realised between 2002-2007. In 2007 His Holiness, the Dalai Lama, held a consecration ritual and Buddhist teachings in the restored temples of Nako. (NRPP) The NRPP is associated to the national research network CHWH and therefore the conception of a special view relating to this research object was an obvious choice. The mission statement of the NRPP “Preserving the past in order to serve the future” (NRPP) underlined the potential for a scientific examination for the geo-visualisation of cultural heritage.

3 Defining the concept of ‘Virtual Nako’ Based on the collected data and outcomes of the NRPP, requirements for an interactive special view had to be formulated and outlined. This task led to the idea of ‘Virtual Nako’ - a 3D digital reconstruction of the Nako temple complex embedded in the virtual surroundings of Google Earth. In this manner an easy to install and widespread application represented the only system requirement. Furthermore the geospatial location and placement of the model on its exact position in the Himalayan mountain range and the integration of additional multimedia content (text, images, VR-panoramas, map-overlays) were assured by using Google Earth as a platform. The added value given by a 3-dimensional perspective in combination with an interactive and intuitive navigation concept allows the user to explore and learn about cultural objects more effectively and intensely. Further emphasis was put on visualizing the structural changes of the temple complex before and after the restoration in a comprehensible way and thus offering the user a direct comparison between different periods.

4 The 3D modelling workflow The composition of the special view ‘Virtual Nako’ followed a standardised workflow from data acquisition, over the 3D modelling process to the integration of supplemental multimedia content. In the

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following the different implementation stages of the concept will be discussed in more detail. 4.1 Base data The level of detail and quality of a 3D model is strongly depending on the available base data. Fortunately the data collected by the NRPP offered a large variety of pictures, architectural plans and drawings. Furthermore the expertise and knowledge of scholars from the national research network assured the visualisation quality and correctness.

Fig. 1: Architectural floor plans of the temple complex in Nako (Source: NRPP 2003) (colour version on CD-ROM)

The collection of pictures from the online photo community Flickr (FLICKR) provided some interesting viewing angles of the temples, where the available data from the NRPP was not sufficient. 4.2 From scratch to a 3D-model In order to expound the characteristic architectural elements of the temple complex and its geo-localisation a consistent visualisation workflow and the required tools (cp. Fig. 2) had to be defined.


Fig. 2: 3D-modelling workflow

By starting with the vectorisation of the overview floor plan it was assured, that the sometimes slightly curved and asymmetric temple walls were captured. The depiction of structural alterations during the restoration period was facilitated by two different basement drawings, which show the complex before (~ 2003) and after (~ 2007) the preservation work. In a next step the digitised line data was imported into a 3D modelling software, extruded and transformed into appropriate objects. During this workflow phase special focus was put on the temples’ correct scaling and proportion to each other. The modelling of characteristic stabilizing stone piles that surround the temples represented a significant task. For meeting the requirements of an easily perceptible and differentiated 3D model, textures were produced from the available pictorial information. Adhering to the technical and visual limitations of Google Earth the level of detail and complexity of the buildings and their textures were adjusted in such a way that a pleasing output could be obtained. Following this, a detailed but not photorealistic model, displaying the main features of the temple complex like its shapes, colours and textures was produced.

Fig. 3: Views of the textured 3D models (colour version on CD-ROM)

A supplemental 3D-base block was created on which the 3D model was placed in order to compensate the hanging slope from the complex’s east to north edge. By using the architectural floor plan of the temples (before the restoration work in 2003) as a textural overlay the visual perception of this base block could be improved.

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In a last phase the model was imported into the geo-spatial environment of Google Earth. Its placement was done according to the available satellite imagery by Google Earth and using GPS data recorded during a field trip. A prerequisite for this step was the capability of the modelling software to export into a 3D studio scene file format. Finally the imported 3D objects were optimised concerning their textures’ file size and the amount of polygons to improve overall performance. 4.3 Integration of additional multimedia content A main intention of the special view ‘Virtual Nako’ was the additional integration of descriptive multimedia content. By enrichening the visual information, the application enables a deeper examination and understanding of the shown objects by the user. According to the concept of Google Earth a consistent storyline of interchangeable overlays from small-scale overview maps (globe view) towards large-scale detailed object information (panoramic view) was designed. It consists of the following key elements: x Map overlays: Various maps covering the area of this part of northern India offer a general overview of the research region for detailed geographic orientation. On large-scale level detailed site plans and architectural floor plans enrich the information content. x Textural and pictorial information: Specified, interactive hotspots contain additional textural and pictorial information about the temples, certain sculptures and wall paintings. x Virtual-Reality panoramas: The integration of hotspots with navigable virtual-reality panoramas offers a photo-realistic view and therefore enables direct comparison of the existing temple complex with the 3D model. 4.4 Final composition and summary The final composition represented the last step in the workflow. It included the addition of an imprint, styling of the navigational tree as well as further refinements in the 3D visualisation and addition of multimedia content. The integration into the CHIS as a special view finally provided a wider audience with the possibility to study the cultural heritage of Nako.


Fig. 4: Screenshot in Google Earth (see appendix)

5 Outlook and future development Positive responses from the research network partners and the obvious benefits of digital 3D visualisations for the communication of object characteristics and change in time to a broader audience verified the existing concepts. The further development and refinement of special views like ‘Virtual Nako’ were strongly encouraged. The improvement in the 3D models level of detail as well as the possibilities to add multimedia content and the visualisation of time periods offer a great potential for communicating and preserving information about objects of cultural heritage. A step towards a more immersive 3D visualisation could even improve the depth and quality of the visualised information. Following this concept, tests with a virtual reality wall (single-channel, rear projection) have been conducted at the University of Vienna. Allowing the user to navigate through the sacred temple complex with a traceable joystick and locking glasses offers a new dimension of interaction and immersion. But still the availability, poor usability and high complexity of such VR systems represent a significant obstacle.

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Acknowledgement This research is undertaken within an interdisciplinary project called ‘The Cultural History of the Western Himalaya from the 8th Century’ started in 2007 in Vienna. This National Research Network (NRN), funded by the Austrian Science Fund, includes cartographers, art historians, numismatists, Buddhist philosophers, and Tibetan and Sanskrit philologists. The main objectives of the NRN are to intensify research on the cultural history of the Western Himalayas as well as to develop a mapbased Cultural History Information System (CHIS) for sharing the outcomes with other experts and the interested public.

References Klimburg-Salter, D 2003, ‘The Nako Preservation Project’, In: Orientations, vol. 34, no. 5, pp. 39-45. Kriz, K, Pucher, A, Kinberger, M, Schobesberger, D 2009, ‘Mapping Cultural History of the Western Himalayas’, In: Proceedings of the 24th International Cartographic Conference, Santiago, Chile. Luczanits, C 2003, ‘The 12th Century Buddhist Monuments of Nako’, In: Orientations, vol. 34, no. 5, pp. 46-53. NRPP, Nako Research and Preservation Project, Web: http://univie.ac.at/nako, last accessed 09/04/2010. FLICKR, Flickr Photo Community, Web: http://www.flickr.com, last accessed 09.04.2010. CHWH: http://www.univie.ac.at/chwh CHIS: http://www.univie.ac.at/chis

Challenges and Perspectives for True–3D in Car Navigation

Timo Götzelmann, Jochen Katzer Department of Research and Development, PreDevelopment, NAVIGON AG, Hamburg, Germany

Abstract In the past years car navigation systems have significantly developed. Beside many important features to support drivers the advanced graphics is the most visible part. After starting with simple arrows and numbers, maps were displayed in order to provide hints for the spatial orientation of the driver. Later on, those maps were rendered perspectively in bird’s eye view and finally 3D data was integrated to generate more realistic views using city models and terrain models. However, one drawback of these 3D navigation systems is the use of monoscopic displays. Using these displays, the only way to mediate spatial depth has been to facilitate monoscopic depth cues. Whereas for desktop computers stereoscopic displays are used in order to allow a better depiction of 3D scenes, they were not used for mobile navigation systems yet. Since this application field has specific characteristics and requirements, this paper addresses the challenges and perspectives for the use of (auto–) stereoscopic displays in prospective car navigation systems. Keywords: Stereoscopy, parallax displays, car navigation, embedded systems, computer graphics, human–computer interface.


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1 Introduction Mobile navigation devices are a successful application of cartographic data which becomes evident by the fact that in 2007 there were about 39 million shipments worldwide (Canalys 2008). These personal navigation devices (PND) increasingly make use of the advantages provided by 3D visualisation. Therefore, besides two–dimensional data, a growing amount of three–dimensional data such as 3D terrain models and 3D city models are used to enrich the navigation system’s visualisation. Recent navigation systems even have photorealistic and very detailed 3D graphics using LOD2 city models and terrain models (see Fig. 1). These 3D graphics are usually rendered using a perspective view onto the 3D scene. In order to support the spatial cognition, multiple depth cues are used to provide intuitive hints about distance. Beside monoscopic depth cues (Goldstein 2006) requiring only one eye (e.g., linear perspective, shadows, fog) a stereoscopic depiction of the 3D scene can be generated by rendering two slightly different images (stereopsis). As in human binocular perception, near and far objects can be horizontally shifted (disparity) in both images, depending on their distance. There are numerous technologies which allow projecting rendered views of the 3D scene in the left respectively the right eye in order to enable the binocular depth perception. Whereas stereoscopic systems require special glasses or other viewing aids to direct the images in their designated eyes, this is not needed for autostereoscopic displays. The most common autostereoscopic solution of this type are parallax displays, which consist of a surface of display elements emitting their light in different directions (Halle 1997). Both of them can be applied on conventional LCD monitors as a simple foil which has been adapted to display parameters like size, dot pitch and desired viewing distance. There are two main technologies of those parallax displays provided by various display manufacturers. Parallax barrier displays use a non transparent slit mask foil which overlays the LCD pixel columns.


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Fig. 1. Eight years of development for navigation system graphics – from simple arrow navigation (left) to photorealistic 3D graphics (right) (Hofmann and Obermaier 2009).

Those slits are arranged in such a way that one pixel column can only be seen by the left eye whereas the adjacent pixel column can only seen by the right eye. On the contrary, lenticular foils consist of cylindrical lenses which overlay each pixel column and thus, direct pixel columns in either the left eye or the right eye by optical refraction. Depending on the radius of the cylindrical lenses’ curvature and the optical material’s refractive index the optimal viewing distance can be adjusted. Since the light of the LCD display is only redirected instead of being filtered 3D displays using lenticular foils are usually brighter than these with parallax barriers. The use of stereoscopic display devices can significantly support the spatial cognition of computer generated 3D visualisations (Wanger et al. 1992). For desktop computer systems stereoscopic applications can be found in multiple fields. However, most of them are used in research institutions or in isolated application fields (Ropinski et al. 2007). In the medical field it helps to explore organic structures generated by medical imaging techniques, e.g., for medical intervention planning (Reitinger et al. 2006). Beside the medical field, stereoscopic displays are used to support the understanding in domains like construction of engineering parts and architecture (Diner and Fender 1993). In cartography, stereoscopic viewers are used to support the exploration and editing of geographic data, e.g., the PurVIEW extension (Waite 2007) or the Stereo Analyst extension (Sims applications, yet. Nevertheless, parallax barrier displays showing two different images on the same screen were introduced by Sharp (Sharp Corporation 2005) and used by the OEM supplier Fujitsu Ten for car navigation systems. Their so called “twin view display” (see Fig. 2) allows two different viewers to see different monoscopic images on

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the same display at a time. Whilst the driver can see a monoscopic map guidance the co–driver is able to watch entertainment applications.

Fig. 2. Illustration of two–way viewing angle LCD (dual displays) in dual display mode (left) and normal mode (right) (Sharp Corporation 2005).

Another technique with similar intentions was developed by Bosch (Siedler 2008) and successfully integrated into the Mercedes–Benz cars of their new E- and S–Type series since summer 2009 (Zanker 2008). However those dual view applications only show monoscopic images and thus, do not support the binocular depth perception. However, as stated before, this could support the spatial cognition – and thus, probably also support user orientation and navigation in virtual cartographic environments. Consequently, there is a considerable market for navigation systems which combines cartography with (auto–) stereoscopic displays. This paper is organised as follows: After this introduction, section 2 covers the individual requirements of 3D displays in the scenario of car navigation. Furthermore, section 3 addresses the software specific issues for autostereoscopic displays and section 4 discusses product related constraints of 3D hardware. Finally, section 5 concludes this paper.

2 Requirements of 3D displays for car navigation The application scenario of mobile navigation devices using autostereoscopic displays has particular specifications for the 3D hardware compared to the prevalent main application fields for (auto–) stereoscopic displays like construction and the medical field. The likely biggest constraint in the automotive sector is that legislation and user acceptance does not allow the use of stereoscopic glasses. Nonetheless, autostereoscopic displays can be employed.


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In the application field of navigation there are a couple of particular specifications for autostereoscopic displays. Investigating the scenario of driving a car using a navigation device there is evidence that in this case single–view displays are more suitable than multi–view displays. Multi– view displays allow a multi–perspective exploration of the 3D scene. However, during the journey the driver only has only a fraction of a second to look at the display. Important features are a good depth resolution and the intuitive interpretability of the 3D scene, e.g., by focus and context techniques. Despite rather bad light conditions in driving scenarios the successful operation of head tracking techniques in vehicles has been shown (e.g., (Shilbayeh and Iskandarani 2005), (Lee et al. 2006)). Using this technology the restricted optimal horizontal viewing angle (sweet spot) of some single–view displays can be overcome. Finally, the computation of multiple views significantly increases the processing power needed by the embedded system. Since the computational capacity of embedded systems does often not allow for the additional workload necessary for the computation of a multiplicity of 3D views, single–view displays are could be more appropriate. Finally, the horizontal resolution of the display device is divided among the number of views (Dodgson 1997) which may impede the legibility of text. Hence, they could be only used with high resolution LCD displays or need to have an optional switch to toggle between 2D and 3D. An additional fact is that the drivers head’s position relative to the 3D display arranged at the front glass usually does not change significantly when looking at the navigation system’s display. Hence, a fundamental advantage of multi–view displays – the exploration of 3D objects, as practiced in the medical domain – cannot be applied in the navigation context. However, there may be a significant difference between the front glasses in different types of cars (see Fig. 3) and even between different anatomical properties and preferences of individual drivers. Therefore, since autostereoscopic displays are adjusted to a very limited range of optimal viewing distance, a solution has to be found which copes with different distances. A possible way could be lenticular arrays which vary their refraction. In order to switch autostereoscopic displays between 2D mode and 3D mode, so called electrically addressable birefringent lenses (Woodgate and Harrold 2003) are used to toggle the refraction of lenticular arrays between two specific values. Using a similar technique, in future it could be conceivable to have multiple levels of refraction and thus, multiple optimal viewing distances. Moreover, there are car related technical requirements and constraints, too. These displays should be heat resistant in order to allow

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unproblematic operation in cars even in summer. Furthermore, lenticular foils will likely more useful than parallax barriers, since the brightness of displays in cars is very important to ensure readability even on sunny days.

Fig. 3. Distance between driver’s position and installed PND varies amongst different cars.

Beside that, as for conventional navigation devices autostereoscopic displays should also incorporate touch screen functionality. Manufacturers have to decide whether they want to integrate both components, i.e., the touch screen foil and the 3D foil. In case of resistive touch screen technology there is likely only the possibility to arrange them above the 3D foil. However, since for capacity based touch screen foils there is no need for the exertion of pressure on the desired display location it could be even arranged below the 3D foil and thus, it could be directly integrated with the display component. Another advantage of these capacity based touch screens is a higher light efficiency (Holzinger 2003). Nonetheless, depending on production constraints the overall thickness of the 3D foil could impede its application on the touch screen. At the moment the resistive technology dominates the PND market, but recently there are also PNDs available on the market using capacitive touch screens (e.g., (Hoffmann and Obermaier 2009)). An advantage of the automotive application field is that current mobile navigation systems facilitate displays with a diagonal size up to 5 inches. Even if their diagonal size will grow to 8 inches in the next couple of years, the limited viewing angle is less important than for desktop monitors with considerably larger horizontal sizes because of their still small horizontal size.


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3 Methods for True–3D in car navigation Beside hardware considerations for autostereoscopic displays using mobile navigation devices there are also problem related requirements for the rendering approaches. Since the computational performance of embedded systems is usually rather limited compared to desktop systems, strategies have to be found to decrease the computational workload. As stated in section 2 the use of single–view displays has computational advantages. By an increasing number of views the computational workload for transformations of the cartographic geometry onto the screen grows linearly. This may lead to a significant difference in timings, even if the embedded system employs a dedicated graphics accelerator. However, depending on the capabilities of the graphics processor, shader programmes can used in order to generate the stereoscopic image efficiently. Another option to limit the computational workload is to decrease the amount of geometric data used for the mobile navigation system’s visualisation. Based on the assumption that the available resolution decreases by a growing number of views, the cartographic data needs to be less detailed for multiple views than for one view. This can be done for example by a higher level of generalisation for polylines and polygons in cartographic data to be visualised. Furthermore, there is evidence that binocular depth perception can considered as an independent depth cue (Julesz 1964). Hence, for mobile navigation devices this can be used as an additional level of freedom for visualisation. The rendering parameters could be influenced dynamically in order to individually adjust the stereoscopic presentation to the users’ demands. One central question to address in future is which autostereoscopic methods could be used in order to introduce users in the new technology.

4 Product related considerations for suppliers From the economic and managing point of view there a several requirements regarding the supplied product 3D display. The price and the manufacturing capacity for 3D display units should be suitable for the mass market. For PND manufacturers this leads to the question for either using integrated 3D displays or individual 3D foils which are adapted to existing embedded systems’ displays. In terms of manufacturing quality integrated 3D displays would certainly be the optimal choice. However, PND producers have long–time experience with monoscopic display

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suppliers and the usability of their products in PNDs. Thus, adapting individual 3D foils on independently designed PNDs may reduce the complexity of these products. Furthermore, if PND producers consider autostereoscopy as an optional feature, the overall project risk related to the product can be reduced significantly. Hence, 3D display manufactures should incorporate these considerations for their future product portfolio. As with many new technologies, the user acceptance and thus, the market penetration of autostereoscopic displays is still cautious. However, mobile navigation devices have the potential for opening a mass market for autostereoscopic displays. Despite 3D TV is announced to do so since a couple of years, it still faces a couple of important challenges (Onural et al. 2006). Amongst other things the standardisation and the sparse availability of 3D media is still upon discussion. Similarly, there are the first series of mobile phones using autostereoscopic displays (e.g., (Flack et al. 2007)), which have also the issue of content creation for pictures and movies, but can also run software which renders stereoscopic images, e.g., mobile computer games. For mobile navigation devices, the complete content creation can be automatically done by rendering the cartographic data in a stereoscopic manner. It should also be considered, that the potential target group of True–3D PND consumers likely differs from expert users of the medical field, engineers, architecture etc. In contrast, they possibly have to be convinced immediately on the POS, and as with many consumer–electronic products it is likely that they will not invest much time learning to use autostereoscopic visualisations. Hence, techniques have to be used which allow a fast and intuitive introduction in this novel technology.

5 Conclusion This paper introduced the challenges of (auto–) stereoscopic displays for the use in mobile navigation systems. It pointed out that the application scenario of PNDs significantly differs from desktop applications and which individual hardware requirements arise from this special use case. Based on these requirements some prospective solutions were suggested in order to overcome use case related issues. Stereoscopic visualisation of cartographic data on mobile devices is a computational expensive task. A significant part of the computation linearly depends on the number of stereoscopic views used concurrently. The effort of this part is directly dependent on the complexity of the cartographic data. Hence, it is important to use sophisticated methods to reduce this complexity without


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influencing the visualisation’s quality. Finally, this paper addressed some marketing related considerations for manufacturers of stereoscopic displays and PND producers. If these questions are addressed autostereoscopic mobile navigation devices have the potential to support cars drivers in near future.

References Canalys Ltd. (2008) Global Mobile Navigation Device Shipments Hit 39 Million in 2007, Research Release, Canalys Ltd., 06.03.2008 Diner DB, Fender DH (1993) Human Engineering in Stereoscopic Viewing Devices, Advances in Computer Vision and Machine Intelligence, Springer, Berlin Heidelberg New York Dodgson NA (1997) Autostereo displays: 3D without glasses, Proceedings of Electronic Information Displays, pp. 1–5 Flack J, Harrold J, Woodgate GJ (2007) A Prototype 3D Mobile Phone Equipped with a Next Generation Autostereoscopic Display, Proceedings of the SPIE 6490, SPIE, pp. 64900M.1–64900M.12 Goldstein EB (2006) Sensation and Perception, 7th edition, Wadsworth Publishing, Belmont California Halle M (1997) Autostereoscopic Displays and Computer Graphics, Computer Graphics, ACM Press, 31(2): 58–62 Hoffmann M, Obermaier A. (2009) A New Age of Navigation is Dawning: the New, Premium NAVIGON 8410 Navigator, Press Release, Navigon AG, 14.07.2009 Holzinger A (2003) Finger Instead of Mouse: Touch Screens as a means of enhancing Universal Access, Lecture Notes in Computer Science, Springer, 2615: 387–397 Julesz B (1964) Binocular Depth Perception without Familiarity Cues, Science, American Association for the Advancement of Science, 145(3630): 356–362 Lee JE, Kim YG, Kim SJ, Jang MS, Lee SJ, Park MC, Park GT (2006) Head Detection and Tracking for the Car Occupant’s Pose Recognition, Lecture Notes in Computer Science, Springer, 4031: 540–547 Onural L, Sikora T, Ostermann J, Smolic A, Civanlar R, Watson J (2006) An Assessement of 3DTV Technologies, Proceedings of the NAB Broadcast Engineering Conference, pp. 456–467 Reitinger B, Bornik A, Beichel R, Schmalstieg D (2006) Liver Surgery Planning Using Virtual Reality, IEEE Computer Graphics and Applications, IEEE Computer Society, 26(6): 36–47 Ropinski T, Steinicke F, Bruder G, Hinrichs K (2007) Focus+Context Resolution Adaption for Autostereoscopic Displays, Lecture Notes in Computer Science, Springer, 4569: 188–193

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Sharp Corporation (2005) Sharp to Mass Produce World’s First LCD to Simultaneously Display Different Information in Right and Left Viewing Directions, Press Release 05–020, Sharp Corporation, 14.07.2005 Shilbayeh NF, Iskandarani MZ (2005) Wireless control of vehicle mirror system using head movement and PIC microcontroller, Journal of Computer Science, Science Publications, 1(2): 182–188 Siedler J (2008) "Dual View" from Bosch: One Screen for Two Programs Separate Information for Driver and Passenger, Press Release PI6025, Robert Bosch GmbH, 01.02.2008 Sims J (2008) ERDAS Extending ArcGIS Extension Offerings, Press Release, ERDAS Inc., 09.12.2008 Waite J (2007) ESRI Canada and International Systemap Corp. (I.S.M.) Announce Distribution Agreement for PurVIEW, Press Release, ESRI Canada Limited, 25.04.2007 Wanger LC, Ferwerda JA, Greenberg DP (1992) Perceiving Spatial Relationships in Computer–Generated Images, IEEE Computer Graphics and Applications, IEEE Computer Society Press, 12(3): 44–51, 54–58 Woodgate GJ, Harrold J (2003) High Efficiency Reconfigurable 2D/3D Autostereoscopic Display, SID Symposium Digest of Technical Papers, Society for Information Display, 34(1): 394–397 Zanker W (2008) Innovative SPLITVIEW Technology: Mercedes–Benz S–Class: Two Programmes on a Screen, Press Release, Daimler AG, 10.12.2008

Holographic Relief Map Production by using Topographic Line Maps (Digital Carto-Holograms)

H. Polat Dalkiran1, Servet Özağaç1, Hakan Büyükbayrak2 1 2

General Command of Mapping, Ankara, Turkey MTM Bilisim A.S., Kocaeli, Turkey

Abstract Most of the inventions in the history discovered by accidentally or inspire of irrelevant association between things. In most cases, somewhere in time, someone else has already imagined it before, but has not been materialized yet. It is so hard to match the idea and the final product in reality, and therefore many of people throws their ideas to the mind trash. But addiction to the idea prepares all the circumstances and brings every possible opportunity to make it real. The thought of a Digital Carto-Holograms (DCH) or Holographic Relief Map (HRM) came into mind such a way a few years ago. It was so popular on those days to have 3D Hologram Eye on the cell-phone’s screen among teens. This idea was a perfect practical marketing strategy for a production company. On the other hand it was an innovative object to a person who manufactures Plastic Relief Maps (PRM). Main problems with the PRM were inflexibility, lack of depicting objects without their heights and aligning features on the plastic sheet with the relief itself. It could be possible to eliminate these disadvantages of PRM with DCH. After preparing theoretical background for over 5 years, it was possible to create the frontier of DCH by using sample vector map data within six months. The Digital Elevation Model (DEM) of the terrain was used to create the perspective, Topographic Line Map (TLM) data, such as line, point and area features were converted to 3D objects, in place of imaginary 2D map symbols, and the aerial photograph to give more realistic view. Exaggeration was implemented on the 3D models to prevent from vanishing on the terrain. After finishing this 3D TLM, it was possible M. Buchroithner (ed.), True-3D in Cartography: Autostereoscopic and Solid Visualisation of Geodata, Lecture Notes in Geoinformation and Cartography, DOI 10.1007/978-3-642-12272-9_26, © Springer-Verlag Berlin Heidelberg 2012

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H. Polat Dalkiran, Servet Özağaç, Hakan Büyükbayrak

to edit the model by using Autodesk’s 3D Studio Max software. The model then posed on a suitable film to produce the Computer Generated Hologram (CGH). In this paper you’ll find the story of this product, benefits of holographic techniques for relief maps, development phases, suggested procedures to follow, main problems for such a production line and the product itself. Although it is a demonstration product, there are too many issues have to be solved in the near feature to create 3D TLM for producing thousands of map sheets. This innovation of the very first and primitive Holographic Relief Map (HRM) gives us hope to solve some disadvantages of Classical Plastic Relief Maps. Keywords: Holography, Digital Holographic Cartography, Holomap, Topographic Holomap, Holographic Line Map, Computer Generated Holography, Plastic Relief Map, Hologram, Holographic Relief Map

1 Introduction: What is Holography and Hologram? Holography is one of the most significant discoveries humankind has ever made. Its discovery has had such a profound effect on our lives, that the person who discovered the process in 1947, Dr. Dennis Gabor, Hungarian physicist, received the Nobel Prize in Physics in 1972. (1) His theory was originally intended to increase the resolving power of electron microscopes. Gabor proved his theory not with an electron beam, but with a light beam. The result was the first hologram ever made. The early holograms were legible, but plagued with many imperfections because Gabor did not have the correct light source to make crisp, clear holograms as we can today nor did he use the off axis reference beam. What was the light source he needed? The LASER, which was first made to operate in 1960. LASER stands for light amplification by stimulated emission of radiation. Without the laser, the unique three dimensional imaging characteristics and light phase recreation properties of holography would not exist as we know them today. Two years after the advent of the continuous wave laser, c.1959-1969, Leiht & Upatnieks (at the University of Michigan) reproduced Gabor’s 1947 experiments with the laser, and launched modern holography. (2) Laser light differs drastically from all other light sources, man-made or natural, in one basic way which leads to several startling characteristics. Laser light can be coherent light. Ideally, this means that the light being emitted by the laser is of the same wavelength, and is in phase. (2)

Holographic Relief Map Production by using Topographic Line Maps (Digital Carto-Holograms) 369

Wavelength, usually symbolized by the the Greek letter λ for lambda, and frequency, symbolized by the Greek letter v pronounced nu, have a reciprocal relationship v λ = C. The amplitude is the height or intensity of the wave. For example, a laser rated at 5mW (milliwatts, or thousandth of a watt) would give off light at the same frequency and wavelength as another laser of the same type rated at 1 mW. But the wave heights of the 5 mW laser light would be five times higher than that of the 1 mW laser. The wavelength is the distance from one crest to the next; this is also one cycle. It seems logical that we would need some constant measure of time in order to count the cycles. This constant unit of time is usually one second. Thus the term cycles per second, or cps, which is often referred to as Hertz or Hz (in honor of the German Physicist Heinrich Rudolph Hertz, who discovered radio waves). Wavelengths of visible light are between 400 and 700 nanometers or billionths of a meter in length. (2) In holography, an object is illuminated with a beam of light and the light scattered from this object reaches a recording medium. A reference beam also illuminates the recording medium. Therefore, it is the interference between the object beam and the reference beam that is recorded on the beam, the light diffracted by the reference is identical to the light field which was scattered by the original object. (3) Holography is the only visual recording and playback process that can record our three dimensional world on a two dimensional recording medium and playback this world as a true three dimensional image to our naked eyes. The image displays complete parallax and depth-of-field (parallax is the ability to look around an object to see objects behind it and depth-of-field is the ability to focus through a scene from near to far). The image can be made to float in space either behind, in front of, or straddling the recording medium. (1) The hologram, that is, the medium which contains all the information, is nothing more than a high contrast, very fine grain, black and white photographic film. There are other photosensitive materials such as photochromic thermoplastics and ferro-electric crystals. The film designed especially for holography is capable of very high resolution which is defined as LPI-Lines Per Inch. One way of judging resolution of film or lenses is to see how many distinguishable lines can be resolved within a certain width, in this case it's a millimeter. Relatively slow film such as Kodak Pan X can resolve 90 lines per millimeter (depending on processing), while a good film designed for holography, such as AGFA Gaevert 8E75 is able to resolve up to 3000 lines/mm. Holographic film is

370


also especially prepared to be sensitive to a certain wave length of light and each type of film is given a code number - AGFA 8E75 is sensitive in the red region and thus is used with ruby or HeNe lasers; Kodak 649F is also, however, about 10 times slower. Kodak 120 plate or SO173 film is very similar to AGFA 8E75 but not quite as sensitive. (2) It’ll be very useful to understand the hologram by comparing with the photograph. A photograph is basically the recording of the differing intensities of the light reflected by the object and imaged by a lens. The light is incoherent, therefore, there are many different wavelengths of light reflecting from the object and even the light of the same wavelength is out of phase. The emulsion of film will react to the light image focused by the lens and the chemical change of the silver halide molecules will result from the photon bombardment. There is a point to point correspondence between the object and the emulsion. On the other hand, a hologram is not a recording of a focused image as in photography, but the recording of the interference of laser light waves that are bouncing off the object with another coherent laser beam, i.e., a reference beam which will be described below. (2)

Fig. 1. A basic holography system. (1) (colour version on CD-ROM)

This particular system has five basic optical components. They are the laser (L), beam splitter (BS), directional mirrors (M), diverging lenses (DL), and the parabolic mirror (PM). In addition to the optical components, there is the object or scene (OS), the photographic plate holder (PH), the table mounts, the optical holders, and the optical table. (1)


Using the diagram in Fig. 1, here's what happens during the recording process. The laser beam from the laser (L) travels to the first directional mirror (M) and is reflected to the beam splitter (BS). At the beam splitter, the beam is split into 2 beams. These 2 beams are given names. One is the reference beam (R) and the other is the object beam (O). The reference beam (R) travels through the beam splitter to a second directional mirror (M) and continues through a diverging lens (DL) to a parabolic mirror (PM) that reflects and spreads the beam to the recording plate (PH). At the same time, the object beam (O) travels through a diverging lens (DL) that illuminates the three dimensional object scenes (OS) which then reflects the laser beam to the recording plate (PH). The interference of the light from the reference beam and the object's reflected light at the recording plate creates a hologram within the hologram plate at the microscopic level. After the plate is processed, it is placed back in the plate holder. The object is removed and the reference beam is allowed to illuminate the plate. Looking through the plate from the opposite side that the reference beam is illuminating the plate, you can see the original object suspended in space, as if the original object were still there. (1) There are two main types of holograms; x Transmission Hologram: This hologram is viewed by placing a light source behind the hologram and looking through it (like a window). The hologram is recorded in a two-dimensional format on the film plate.(4) Reconstruction of the hologram and readouts are shown on Fig. 2.

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Fig. 2. Virtual and real image reconstruction (colour version on CD-ROM)

x Reflection Hologram: holographic fringes being recorded in threedimensions. This hologram is viewed by looking at the reflection of a light source in the hologram (like a mirror). This type of hologram depends on the (Bragg reflection) on the film plate.(4) Reconstruction of the hologram and readouts are shown on Fig. 3.

Fig. 3. Reflection hologram(colour version on CD-ROM)


2 What is a Plastic Relief Map (PRM)?

Fig. 4. Production of a plastic relief map(colour version on CD-ROM)

A PRM is a kind of hard-copy map which has the ability to depict the real 3D terrain model of a relevant map extent. It’s commonly so hard for a human to recognize and visualize the elevation model of a terrain from a printed Topographic Line Map, unless one is not an expert. Without an accurate recognition of 3D information, map users could make wrong decisions and it could cause unpredictable failures of projects and works. It is one of the main objectives for the cartographers to transfer most realistic information about land/earth data. Thus, the most common way to do it, imprinting 2D maps on a PRM plates. This simple demonstration of the PRM production system has five steps (Fig. 4). Cartographic Vector Data are prepared by using Karto25 (TLM Production System) which is based on ESRI’s ArcInfo Workstation and developed by General Command of Mapping, Turkiye. (A) Once the postscript of the map sheet is ready, colour separation is done by Kodak Quantum II 800 CPT and plastic plates are printed by Heidelberg Trendsetter CD 102. (B) Digital Elevation Model (DEM) is prepared by using ArcInfo Grid module and converted to Grid ASCII format. WORKNC software is used for converting the ASCII file to the WNC format. (C) After preparation of the DEM data for CNC Machine, TNC software is used for sending data to milling head. The CNC machine

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carves the Midform block, a special soft and durable material in the industry more than still, by using 3D coordinates received from the computer. (D) The preparation of 3D Midform block, a special machine is used for molding the Plastic Map Sheet. (E) The final PRM product of the topographic map.

3 Computer Generated Holography (CGH) Basically the CGH can be defined as the process of synthetically producing fringe patterns from digital data by using computational methods. A holographic image can be generated e.g. by digitally computing a holographic interference pattern and printing it onto a mask or film for subsequent illumination by suitable coherent light source.(5) Holographic image can be reconstructed by a holographic 3D display. In recent times the term “Computer Generated Holography” is increasingly being used to denote the whole process chain of synthetically preparing holographic light wavefronts suitable for observation.(6) Optical holograms need a real object for recording, contrary, CGH does not require a real object, has unlimited capacity of creating 3D holograms and can be reconstructed with many different medium or devices. Besides the advantages of CGH, there are obvious lower and upper bounds in terms of computational speed, image quality, resolution and adherence to the real object. Wavefront calculations are computationally very intensive; even with modern mathematical techniques and high-end computing equipment, real-time computation is tricky. There have been many different methods for CGHs proposed for calculating holographic interference patterns. (7,8,9,10,11) Basically the computational algorithms can be grouped in two main concepts in holography. x Fourier Transform (FT) Method: Fourier Transformation is used to simulate the propagation of each plane of depth of the object to the hologram plane. The FT concept was first introduced by Brown and Lohmann (12). Calculation of the light propagation from 3D objects is performed according to the usual parabolic approximation to the Fresnel-Kirchhoff diffraction integral. The wavefront to be reconstructed by the hologram is, therefore, the superposition of the Fourier transforms of each object plane in depth, modified by a quadric phase factor. The vast majority of hologram computation methods employed so far have been predicated on the understanding that the field distribution seen by the viewer will be very close to the two dimensional


Fourier Transform of amplitude arrangement in plane of the hologram. (13)That is,

where the coordinates (μ,v) in the output plane are simply the hologramplane coordinates (x,y) scaled by a constant factor determined by specific reconstruction geometry chosen. That a simple encoding of the hologram could proceed directly from an inverse Fourier description of the output amplitudes is quite ingenious, and the pioneers of the methods by which was accomplished must be commended. (14) x Point Source Holograms: The second computational strategy is based on the source concept, where the object is broken down in self-luminous points. An elementary hologram is calculated for every point source and the final hologram is synthesized by superimposing all the elementary holograms. This concept has been first reported by Waters (15) whose major assumption originated with Rogers (16) who recognized that a Fresnel zone plate could be considered a special case of the hologram proposed by Gabor. But, as far as most of the object points were nonzero the computational complexity of the point-source concept was much higher than in the Fourier transformation concept. Another concept which leads to Point-Source CGHs is the Ray tracing method. Ray tracing is perhaps the simplest method of computer generated holography to visualize. Essentially, the path length difference between the distance a virtual “reference beam” and a virtual “object beam” have to travel is calculated; this will give the relative phase of the scattered object beam. (5)

4 What is a Digital Carto-Hologram(DCH) or Digital Holographic Relief Map (D-HRM)? It is said that printed media will be used more over 20 years from now on. So the need for PRM will gain more importance for the map users. Besides the advantages of the PRM, there are also some very important disadvantages such as inflexibility of the medium and being not suitable for carrying which restrict the usability of the PRM on the field. The idea behind DCH is to merge the capabilities of PRMs and Holography and append more abilities on it. An DCH is more than a 3D

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reconstruction of a Topographic Line Map on a 2D flat medium. There can be found numerous usages for the DCH which will supersede Paper Maps (PM) and PRMs. Table-1 lists some of the advantages and disadvantages of DCH, PRM and PM. Table 1. Comparison of DCH, PRM and PM Feature

DCH

PRM

PM

Perception of 3D topography Full of the terrain

Full

Pseudo

Perception of 3D view of the Yes geographic features Automated production direct Needs Improvement from TLM data Cost for the same size $200-$2000 per sheet Ability for tiling of large Yes areas Flexibility of the medium Yes Ability to show animated Yes information Printing quality High Deformation of printed data Low on the medium Ability to store layered Yes information Resolution of the medium

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