CARTOGRAPHIC DESIGN IN 3D MAPS

Transcription

1 CARTOGRAPHIC DESIGN IN 3D MAPS Petrovic, D. University of Ljubljana, Faculty of Civil and Geodetic Engineering, Geodetic Institute of Slovenia, Jamova 2, 1000 Ljubljana, Slovenia. Fax: dusan.petrovic@geod-is.si ABSTRACT A computer technology development and a wide range of computer tools have brought many changes in theoretical fundaments of cartography. Visualisation techniques and possibilities for communication between user and computers give an opportunity to design new landscape representations. They would enable users better terrain interpretation resulted in more efficient and complete spatial data capturing corresponding to the traditional two-dimensional paper or screen maps. One of those possibilities is producing three-dimensional cartographic model (3D map) as a new approach in landscape presentation. The main benefit of 3D maps regarding 2D maps is more realistic and user-friendlier height presentation. Besides this 3D maps offers many new possibilities of use: simulations of moving in real time, simulations of placing new objects on landscape, dynamic phenomena analyses, etc. Users can observe 3D map on computer screen, where proper SW offers him to choose a viewpoint and a distance. But it is also possible to print selected view on a paper sheet and use it as a traditional perspective or ordinary 2D map. An attempt for defining 3D maps cartographic design principles is described in a paper. Principles for traditional 2D maps design have been developed for decades and make strong base for every map produced, while such principles for 3D maps do not exist. Good 3D map has to satisfy main theoretical requirements for cartographic presentation and also gives advantages to map-readers. First of all, I ve tried to confirm a right to call these new products as a 3D map with regard to official theoretical definitions about maps. 3D maps design is slightly different according to the weaving direction on a scene. Use of Bertin s graphical variables is extended into a 3D space. Levels of detainees have to be considered both from point of contests and also according type of cartographic presentation. Particular 3D cartographic signs affect in local changing of DTM. Some other specific problems like covered area behind relief obstacles; object s shadows and accentuation are also described. All the suggested solutions have been proved on a prototype 3D topographic-mountain map of Kamniske and Savinjske Alps. This is a small mountain ridge in the north part of Slovenia, with heights up to 2500 metres. Besides high mountains prototype region area covers also foothills and a plain with towns that are most common start points for mountaineers. The main point is topographical content design while a technology solution is on the second plan. Keywords: 3-dimensional maps, map visualization, map design, cartographic symbolization 1. INTRODUCTION A computer technology development and virtual reality techniques have brought many changes in theoretical fundaments of cartography. Visualization techniques and possibilities for communication between users and computers give an opportunity to design new landscape representations. The most often-used map media in a past, a paper, is being replaced with computer screens and other contemporary visualization media. User is not only the observer of the map, in the interactive environment user become a mapmaker himself, he can follow different dynamical phenomenon or even move himself in a virtual model of a landscape. One of those new possibilities is landscape visualization where view direction is not vertical, like in common maps. Presentations, having view direction inclined corresponding horizontal plane are very well known for centuries as perspective or panoramic maps, but nowadays technology allows us to prepare and produce them according to cartographic science principles. There are also the huge amount of available topographic data stored with three dimensions (3D data), which are essential for every 3D presentation. Obviously, the majority of incline presentations try to present the landscape as similar to the reality, as a photorealistic presentation. Those ones are surely close to humans perception and therefore offer the best scene recognition. But, the lack of photorealistic presentations is limited informational value, which is one of the key map purposes. Such presentations don t consider two of the main cartographic principles cartographic symbolization and cartographic generalization. Proceedings of the 21 st International Cartographic Conference (ICC) Durban, South Africa, August 2003 Cartographic Renaissance Hosted by The International Cartographic Association (ICA) ISBN: Produced by: Document Transformation Technologies

2 2. CARTOGRAPHIC PRESENTATIONS Using computer technology in modern map production and map use, supplemented by GIS products, limits between cartographic source data, cartographic models and maps themselves become more and more indistinct. According an official ICA definition, map is a symbolized image of geographical reality, representing selected features or characteristics, resulting from the creative effort of its author's execution of choices, and is designed for use when spatial relationships are of primary relevance [1]. A map is consequently an image, seen by the final observer the human. In a human body an image is constructed in brains as a result of sense organs recognition. Therefore it is not important at all either we sense a map by eyes, ears or fingers (tactile maps) neither it is important what kind of media carries the map. A map so cannot be analogue or digital, only map data as the source for visualising map can be in analogous or in digital form and also map production procedures can be analogue or digital. In the analogue map production procedures data capturing and data preparation have been completely adopted to the final map design. Each data has been stored - in a past on cuprum plates, later on glass plates or on plastics - according its importance, position, size and shape, as it should appear on the map. In computer environment data are usually stored in various vector topographic databases, where every object can be stored as a point, line or closed polygon. Data model, where every object is defined with pair of coordinates in horizontal plane only is known as two-dimensional (2D). Soon, need for defining object also with height appeared, since heights are essential for every relief or elevation analyses. Data model, where height is added as an attribute is called two-and-half dimensional (2.5D), while in true three-dimensional model (3D) every point is described with a set of three coordinates. Topologically organized data offer various different queries and spatial analyses as the main purpose of topographic databases, indeed. If we want to produce a map as a result of topographic database, two very important procedures have to be done additionally cartographic symbolization and cartographic generalization. We can call these procedures as a cartographic visualization of a database. Visualization of 2D or 2.5D model allow us only to prepare a traditional ground plan (vertical) map while 3D model offer various different presentations, presented in Figure 1. Basically, we have two different types of looking on a scene: orthogonal and perspective. Projective beams in orthogonal views are parallel while in perspective view they converge into a point called focus. According the angle between horizontal plane and view direction three typical situations appear: vertical view, parallel view and (most general) incline view. Combining type and direction we get six different views [2], presented in Figure 1. Upper figures (in black) present regular grid in a horizontal plane (heights set to zero) while lower figures (in blue) represent real terrain model, presented by regular grid. Figure 1. Regular horizontal grid and terrain model as grid, presented by six typical views

3 In general three of those presented typical views are useful in cartographic presentations: orthogonal vertical view for ground plane (traditional 2D) maps, orthogonal inclined for various panoramic maps, and perspective (either parallel or inclined, since there are no real difference), but sometimes also other views offer information of specific interest and can be used for presentation. Which of those views can then be called 3D map? All maps are made from the same, three-dimensional cartographic model. All of them can present height as a third dimension (vertical view indirectly, e.g. using contours). Finally, all of them are usually presented on a screen, which is 2D media. Are they 2D or 3D maps? 3. PHOTOREALISTIC IMAGE OR SYMBOLIC PICTURE? Three-dimensional landscape presentation can be called a map only if satisfies some requirements, that worth for traditional 2D maps, as follows:! every presented object is defined with its geographical position in selected coordinate system and this position have to be accessible to the user,! objects and phenomenon are projected from Earth surface to the selected (usually plane) coordinate system according exact cartographic projections, that assured deformations in regulation sizes,! cartographic symbols as an alphabet of the map archive the communication and the information transfer between cartographer and user and! cartographic generalization principles define the level of map detainees. Authors usually neglect those requirements and determinate that 3D map is a computer made, mathematical defined, three-dimensional high-realistic landscape presentation together with all nature and artificial objects and phenomenon [3]. Those maps are mostly observed on the computer screen, which is 2D media, while third dimension is recognised by using set of different effects, like imitation of natural elements and materials, shining, lighting, shadows, etc. The goal is to produce photorealistic image as similar to the real world as possible. These kinds of presentations allow users to observe the presentation exactly on the same way like observe reality. But, if users really want such presentations, why using traditional 2D maps instead of aerophoto or satellite images? The answer is information completeness! Photorealistic images, like ones on the Figure 2, are acceptable only for very near objects, presented in a large scale. Due to limited media (screen) resolution and human perception capabilities all distant objects are not sharp and therefore can t be interpreted and recognised successfully. Figure 2. Examples of computer made photorealistic images [4,5]. Traditional 2D maps have at least two advantages towards orthophoto images or high-resolution satellite images: cartographic symbolization and cartographic generalization. Principles for traditional 2D maps design have been developed for decades and make strong base for every map produced, while such principles for 3D maps do not exist. Good 3D map has to satisfy main theoretical requirements for cartographic presentation and also gives advantages to map-readers. The map couldn t just try to copy the reality; it has to consider specifics of human perception, while its main purpose is to inform users about situation of presented area. On the other hand, we have to know, that efficient and successful map reading is mostly the consequence of users knowledge and experience. It is quite understandable that users prefer photorealistic 3D presentations since they don t need any specific knowledge to read them. But, maybe it is enough to perform perspective view in 3D presentations, while particular objects are presented by cartographic symbols! Cartographers are chosen to find better 3D presentations and teach the users to read them; we have to partly adept to the users, partly teach them and find the right balance between both tasks [6]. Three-dimensional (3D) map is therefore cartographic landscape presentation in perspective view, where topographic objects and phenomenon are presented by cartographic symbols, explained in a legend.

4 4. DESIGNING OF 3D MAPS CARTOGRAPHIC SYMBOLS Every object in reality is a 3D body. Some of them have one or two predominant dimensions and this influences on cartographers chose how to present them on the map. In 2D maps design we use point, line and area symbols. Using six Bertin s variables (colour, shape, texture, direction, size and brightness) various sets of different map symbols can be made [7]. In 3D presentations basic graphical elements (point, line, area polygon) are supplemented with volumetric 3D object. Multimedia computer technology offers also different visual and audio effects, static and dynamic forms. The foundation for each 3D cartographic model is terrain model. One can be most usually described as a triangular or rectangular mesh. All landscape objects and phenomena are placed on the terrain model, presented with appropriate symbol (Figure 3). Geometric point 3D symbols are suitable for presenting mostly man-made point objects, like buildings, churches, monuments, etc (Figure 3a). Such symbol consists of simple geometric bodies. Its size and shape is fixed for selected object type and selected level of detail. Some point-like objects, especially natural-made, like trees, bushes, waterfalls etc. can be better presented with typical realistic (real-like) point 3D symbols (Figure 3b). a) b) c) d) Figure 3. a) Geometric and b) realistic point 3D symbol, c) line 3D symbol and d) surface in a space. Objects with one predominant dimension and mostly fixed other dimensions, like roads, railways, power lines, oil pipelines, smaller watercourses, fences etc. are usually presented as a line 3D symbols (Figure 3c). When objects are entirely draped over the relief (watercourses, paths) the height of particular point is the same as DTM height and therefore third coordinate is not necessary. In most cases, linear objects don t lie exactly on the terrain (road and railroad bridges and tunnels, cable-cars, power-lines) and height data is essential for every point. Area 3D symbols can be used for objects where only one dimension (often height) is mostly fixed (Figure 3d). Such objects can be forest, orchard, or even blanket of snow. Area 3D symbols can be constructed as a filled solid body or, most common, as a mesh of points with different density. The last options are volumetric 3D symbols, where every single object is presented with its exact real dimensions along all three coordinate axes. Typical examples are large and important (mostly man-made) objects and also water bodies, like lakes, sea and large rivers. Using of Bertin s variables in 3D presentations is slightly different like in 2D maps. In perspective views close objects are clearly visible and bigger like distant ones. Therefore we cannot use the variation of Bertin s variations only for distinguish different object types. Every object type should have different appearances according to the distance between observation point and an object. Since we cannot perform linear transition we have to decide to limited number of discrete steps different map symbols for the same object type; similar as map symbols for 2D maps at different scales. Usually we call them levels of detail (LOD). Figure 4 shows map symbol for a church in four levels of detail. Symbols for close objects are quite realistic looked, bright, made with irregular shapes and detailed. With increased distance symbols became simplified, darker, less detailed and geometric. 5. EXAMPLES OF 3D PRESENTATIONS Figure 4. 3D cartographic symbol for church in four LOD. All the explained principles have been proved on a prototype 3D topographic-mountain map model of Kamniske and Savinjske Alps. This is a small mountain ridge in the north part of Slovenia, with heights up to 2500 metres. The main

5 point was topographical content design while a technology solution was on the second plan. The selected test area was 7 km 7 km. A complete 3D topographic model has been established as a source for different presentations maps. For better presentation some objects, not exist in reality, have been added. Next task was designing 3D cartographic symbols. Regardless above described principles cartographic 3D symbols for 54 different object types and up to three levels of details for each object type have been designed. They were used for symbolizing 3D cartographic model in test area. Figure 5 shows four examples while many more images can be seen at Figure 5. Examples of 3D cartographic presentations of test area. Since an idea for presenting landscape with 3D symbolic image is infrequent it wasn t an easy task to find and select proper SW for such a project. In fact, it was necessary to combine different SW. In my work, 3D cartographic model was entirely established in Intergraph MGE. Majority of 3D cartographic symbols were designed and worked out in Rhinoceros, while final presentations have been made using World Construction Set. 6. CONCLUSION Three-dimensional cartographic presentations linked with multimedia possibilities and interactivity became the most attractive way of presenting spatial data. Wide options of computer technology and large amount of easily accessed topographic data inspire cartographers and GIS experts in producing photorealistic presentations. But, with these types of presentations we loose the key advantage of maps towards photography and similar presentations we loose high informational, communicational and also artistic value. Three-dimensional presentations have to follow principles of traditional 2D maps not only in mathematical definitions, but also in designing principles. Leaded such cognitions 3D cartographic symbols for different object types and levels of detail have been designed and used in 3D presentations of tested area. Further investigations should capture potential 3D maps users and considering their opinion improve principles of designing 3D cartographic symbols. 7. REFERENCES [1] International Cartographic Association (ICA), Organisation and activities Netherlands Cartographic Society (NVK publikatiereeks). [2] Petrovic, D. 2001: The Principles of Designing Three-Dimensional Map Presentations. Doctoral thesis, University of Ljubljana, Faculty of Civil and Geodetic Engineering. [3] Bandrova, T. 1998: Cartographic Modelling of the Real World. Proceedings of Seminar of Cartography, Volume 1. University of Architecture, Civil Engineering and Geodesy, Sofija.

6 [4] Crampton, J.W. 1999: Online Mapping - Theoretical Context and Practical Applications. V knjigi Cartwright et al. (ed.), Multimedia Cartography, Springer, Berlin. [5] Virtual Terrain Project (VTP), [6] Rojc, B. 1986: A contribution to the map content perception research. Doctoral thesis, University of Ljubljana, Faculty of Civil and Geodetic Engineering. [7] Bertin, J. 1974: Graphische Semiologie. Walter de Gruyter, Berlin.

7 CARTOGRAPHIC DESIGN IN 3D MAPS Petrovic, D. University of Ljubljana, Faculty of Civil and Geodetic Engineering, Geodetic Institute of Slovenia, Jamova 2, 1000 Ljubljana, Slovenia. Fax: dusan.petrovic@geod-is.si Biography Dusan Petrovic, Ph.D. Born in 1969 in Slovenj Gradec, Slovenia. Graduated at University of Ljubljana from electro-technique and geodesy fields in During study spent 6 weeks at Johns Hopkins University in Baltimore, Maryland, USA. Master s degree thesis was Project of National Topographic Map System of Republic of Slovenia; Doctoral thesis titled The Principles of Designing Three-Dimensional Map Presentations obtained in 2001 at the University of Ljubljana, Faculty of Civil and Geodetic Engineering. From 1994 has been worked at the Geodetic Institute of Slovenia, for two years as a Head of cartographic department, actually as an Adviser of manager. Introduced computer technology in map production and founded the National cartographic and topographic system of Republic of Slovenia. At present leads the establishment of complex system of national topographic databases and maps. From 1996 involved in education process at geodesy and at defense-studies undergraduate studies. An assistant professor for cartography and topography at the Faculty of Civil and Geodetic Engineering from Member of High Mountain Cartography ICA Commission, national representative in ICA and president of Orienteering Federation of Slovenia.