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GIS datasets for 3D urban planning
Pergamon
Comput., Environ.and Urban Systems,Vol. 21, No. 2, pp. 159-173, 1997 © 1998ElsevierScienceLtd. All rights reserved Printed in Great Britain 0198-9715/98 $19.00 + 0.00 PII: S0198-9715(97)10005-9
GIS DATASETS FOR 3D URBAN PLANNING Monika Ranzinger and GOnther Gleixner ~ GRINTEC GesmbH, Gesellschaft for Graphische, Maiffredygasse 4/11, A-8010 Graz, Austria ABSTRACT. For decades urban planning was done by drawing plans and building elaborate models from wood and pasteboard. The Austrian Cities of Graz and Vienna are demonstrating that this is a thing of the past - - its threedimensional (3D) computer simulations derived from information of the digital city map are revolutionizing the planning process. The paper deals with the feasibility and potential benefits of a 3D-city model and covers the following topics:
(1) What is a 3D-city model? (2) What is it ased for? (3) Which data is needed for a 3D-city model and where is it derived from? (4) How can a 3D-city model be generated on a regular, operational basis? Results of projects carried out in Graz and Vienna will be shown to demonstrate the operational applicability of a 3D-city model. © 1998 Elsevier
Science Ltd. All rights reserved
INTRODUCTION F o r decades urban planners and architects have used drawings and elaborate wood and pasteboard models to convey their ideas.
Conventional Visualization Techniques Until now mainly non-digital presentation forms have been used in architecture and urban planning: • Model. Based on the drawings of the architect, a wood or pasteboard model of the
building is made. The disadvantage of this technique is that a good model with all realistic details is very expensive. There is also no possibility to see the building in a realistic perspective and making changes to the model is rather complicated and time consuming. 1Tel: 43 316 383706; Fax: 43 316 8370620. 159
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• Perspective drawings. Perspective views of the building are created either by hand or
by means of computer software. Normally only the vertices of a building are constructed. Details such as windows, doors and the surroundings are sketched freehand. The aesthetic impression depends very much on the skills of the draftsman. • Photomontage. A photograph of the building site is used as background for a perspective drawing. By including the actual vicinity of the building this technique gives a more realistic impression. All these methods generally have some drawbacks as regards realistic impression, easy adaption to changes or simple comparison between different variants. As citizens demand more influence in planning processes, new computer-based methods like three-dimensional (3D) computer simulations and animations are called for. We at GRINTEC have long-time experience in applying different digital techniques to "make the future visible". Motivation The origins of our work in this field date back more than ten years. Our first project, which was carried out on behalf of the municipal department for urban planning in Graz, was a computer animation showing different architectural proposals for a new building on F/irberplatz. The surrounding buildings and the simulated camera motion remained unchanged, with the proposed buildings faded in one by one. Existing and new buildings were only depicted as simple blocks with roofs, the display of materials like glass or wood did not look good and took hours to compute. Effects such as shadows and reflections or additional objects such as trees and lamps were not used at all. Compared with today's technical possibilities it was rather low-level and very costly hardware was needed. Just the same, we became fascinated by the new possibilities and developed many ideas for improving the results and reducing the effort and expense for data acquisition. In 1989, when the required hardware was available, we translated one of these ideas into reality: To overlay a standard video film of the building site with computer-generated images of the building. The first operational version of the resulting software package moveX was completed by mid-1991. In the same year a video film produced with moveX won the video and slide contest of Eurographics '91 and was given an award at the International Prix Ars Electronica in Linz.
VIDEO MONTAGE WITH MOVEX moveX - - a video montage system - - combines the advantages of the photomontage technique and computer animation. A video f i l l of the building site is overlayed with computer-generated images of the proposed buildings - - thus the realistic surroundings and the 3D impression of the f i l l are maintained. Source data for moveX simply consists of a video of the building site and the plan or CAD data of the proposed building - - or buildings if different building designs will be visualized, moveX computes, for each frame of the video, the corresponding perspective of
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the new building and overlays the video frame with the computed image. For the viewer, the resulting film gives the impression of the new object already being in its position.
Working with moveX For creating a video with moveX, the following steps have to be performed.
Creation of the Source Video The first step is to create a video film of the building site. Depending on the size of the building project, this can be done by walking round or from a car or by using a helicopter. Computer Aided Design Construction of the Building Additional to the CAD model, the colors and materials of the new building have to be defined. Calculation of Video Parameters A standard video recorder stores 25 frames or 50 half-frames per second. In order to overlay a video film with computer-generated images: • the exact camera position, • the viewing direction, and • the zoom adjustment for every frame of the film have to be known. moveX reconstructs these parameters from the video frames by using "passpoints". Passpoints are special image points with known world coordinates. They should be easily distinguishable from the background and well distributed in the frame and must not lie in one plane. At least five independent passpoints for each frame are needed for calculating the camera parameters. Since the positions of the passpoints in all frames of the video film have to be known to calculate the camera movement, it would take too long to measure them manually. That is why passpoints are tracked automatically by applying pattern recognition and making use of the fact that the position of a passpoint does not change very much between consecutive frames. Thus passpoints have to be manually identified only in the frame in which they appear for the first time. For this process, all images of the video film are digitized and stored by means of special hardware.
Masking Objects such as trees or cars which should remain in front of the new object must not be overlaid by the image of the new object. In these cases the method of masking is applied. Only uncomplicated objects permit one to apply 3D masks, where we add a 3D representation of the object to the CAD description of the planned building. This is quite efficient because the position of the mask has to be specified only once. Complex objects such as cars are difficult to construct with CAD, therefore we manually digitize a 2D mask on screen. This has to be done every fifth to tenth video image. The 2D masks for the frames in between are interpolated using a third-degree polynomial.
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Both 3D and 2D masks give optically satisfying results. Sometimes we have to apply another technique if the objects to be masked are very complex. In this case we create binary mask images. To find, for example, branches of a tree, we use the same classification techniques as for passpoint recognition.
Rendering of the New Building As a result of the previous steps we know all the camera parameters necessary to compute the corresponding perspective view of the new building for every frame of the video film. Each digitized image of the video film is now overlaid with data from the computer-generated images of the building. The resulting images are again recorded on video tape.
"'Parkshop (14"; Vienna One of our first moveX projects was the visualization of a planned parkshop with a shopping center, offices and apartments on behalf of municipal departments for urban planning and for data processing in Vienna. "Parkhaus U4" is situated near an underground station of line 4. The already existing parking garage had to be incorporated into the new building design. Different video sequences approaching and passing the future building by car were recorded. To get an overview of the whole area a pan was filmed from the roof of the hotel directly opposite. Filming a building which does not yet exist is not as easy as it may seem and takes a lot of imagination. The cameraman has to estimate the dimensions of the building to chose suitable views and details. For "Parkshop U4" we filmed a lot of reserve footage to be sure that all required sequences were included. As we did not take care not to include foreground objects in our video, we ended up with quite a lot of masking work to do. We had to mask out cars, street lamps, traffic signs and bushes. We used 2D masks for cars, street lamps and traffic signs and binary masks for bushes. For calculating the camera parameters of the video we used streetlamps, windows of buildings, traffic signs, zebra crossings and other easily identifiable objects as passpoints. The world coordinates of some of these passpoints could be selected from the geographical information system (GIS) of Vienna, others had to be geodetically measured. In the first stage we created a film sequence of about 45 seconds which showed the new building in detail from different perspectives. This film was reviewed by the architect and the staff of the municipal departments. Some changes in the building design resulted from this meeting. Afterwards, the final version of the video was produced. It was computed on a SGI Personal IRIS using our own rendering software, the average computing time for one frame was about 3 minutes.
Administration Building, Deutschlandsberg, Styrla The animation of a planned administration building in a district town in Styria was done to inform the citizens in the vicinity of the proposed development. We encountered several problems when generating the source video: • From two sides the building site was not accessible, so these parts could only be filmed from the bird's-eye view. We used the crane on the neighboring site to shoot this video footage.
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• Adjoining sites were already under construction, which leaves an impression of incompleteness in the resulting video. For the rendering of the new building some nice effects were used. The material for most parts of the facades was planned to be glass, which is why we also filmed the houses across the street and used these images for the reflections in the glass facades. Part of the computer animation is a simulation of the interior. The facades of the houses across the street are used in this sequence to give a realistic view when one looks out of the office windows.
Advantages and Disadvantages of Video Montage The technique of video montage is especially well suited: • for the evaluation of different variants of a planned building, • for development projects, where the surrounding is of critical importance (e.g. in old town centers), and • because videos can be easily copied and can be shown virtually everywhere. Video montage is not the right technique to use: • if adjacent sites or the site itself are already under construction, • if there will be major changes in the surrounding terrain or a redesign of a whole area, and • if the view of the future building is obstructed by too many other objects, which remain in the foreground and have to be masked.
3D-CITY MODEL To be able to make changes to the surrounding of a proposed building and view the results from any viewpoint, one needs a 3D model not only of the new building but of the whole townscape. A 3D-city model (3D-CM) is a special computer representation of all fixed objects (buildings, vegetation, traffic ways and waterways) within a town. It contains all the information necessary to view each object from all sides and the main characteristics to make it recognizable. It is sort of a CAD model of the whole town. One of several pilot projects to test the applicability and potential benefits of a 3D-city model was the computer animation of the proposed "New Jakominiplatz" (Figure 1), which was produced on behalf of the municipal department for urban planning.
Project Jakominiplatz The animation shows Jakominiplatz, the busiest junction for public transport in Graz, as it will appear in Autumn 1996 after two years of rebuilding. The video takes the viewer on a walk around the new square, highlighting the different features of the architectural scheme as one walks along. Finally, one takes a virtual ride on the tram which is already running on its future rails. The layout of the source model for Jakominiplatz was taken from the digital city map. By using plans and photogrammetric interpretation a wire-frame model of the existing objects was generated. For the buildings to be identifiable, mere blocks with roofs are not
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FIGURE 1. Image of the
new
Jakominlplatz.
sufficient. We took a photograph of the fronts of all houses which look onto the square, scanned and rectified them and "glued" them digitally onto the facades of our digital model. Finally, CAD data of the proposed new objects was added to the model. We estimated that almost two thirds of the working time for the animation would have been saved if a 3D model of the Jakominiplatz had already existed and could have been used.
Applications of 3D-City Models 3D-city models can be used in many fields of urban planning: • Analysis o f the present situation. 3D visualizations give a better impression of the surrounding than 2D maps and help pinpoint problem areas where something needs to be done. • Planning and control. Interactive planning of buildings enables planners to show different stages of redevelopment. They can simulate redevelopment plans within seconds in order to compare the new plans with the virtual world around them. Different types of 3D products are necessary during the planning stage. Planners can start with a rather abstract model of the surroundings and add more and more details as the planning process evolves. There are many applications for other urban planning boards as well, e.g. road planners can review traffic signs by controlling whether they can be seen from all directions. • Decision support. Different designs of buildings can be compared directly in their future surrounding, the decision-making process is quicker and more efficient. • P r e s e n t a t i o n . Using the information stored in the 3D-CM documentations, perspective drawings, digital photographs and films of the present townscape overlaid with proposed buildings can be produced. Even virtual worlds can be created,
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enabling citizens to walk through future urban areas and have proposed changes explained to them.
Basic Information for the 3D-City Model Until now 3D-CAD has mostly been used for modeling single buildings or blocks of buildings. Since it takes quite an amount of interactive work to input the data, a 3D-model of a whole town seemed to be too costly. But much of the information necessary for a 3DCM already exist in the digital city maps. Vienna and smaller Austrian cities such as Graz or Linz started to build databases for the digital city map in the 1980s. By now they have stored all the basic layers, such as topography, road network, parcels, houses, parks and grassland, and have collected a lot of additional information as well. To collect or store these data once again in a different format for a 3D model would be inefficient. That is why GRINTEC developed the software package C,O-3DM (GIS objects to 3D models) which automatically converts GIS data into a 3D model. C,O-3DMcurrently reads D X F data and generates D X F 3D faces or 3D triangles. Figure 2 gives an overview of GO3DM. When the city of Vienna acquired GO-3DMin 1995, detailed specifications for collecting, structuring and storing all information necessary for the 3D-CM were laid down. These include information on the height of objects, roof-types or images of facades. The information is all going to be stored and managed in the database of the "Wiener Mehrzweckkarte" (Vienna multipurpose map, MZK). Thus the GIS will remain the central tool for data storage and data management. Changes made in the 3D model will not be saved over a longer period, instead the corresponding information will be edited in the M Z K database. GO-3DM and the specifications for data capture - - photogrammetry is used to collect heights and roof lines - - have already been tested in several new pilot projects and have achieved good results. Only minimal editing - - mostly to correct complicated roofs - was required for the automatically generated 3D model. By using this method, the city of Vienna can go on using the M Z K for its usual applications and have the base data ready for the 3D-CM. Currently about 20 employees of the city of Vienna are trained in the use of GO-3DM and of 3DSTUDIOTM, the software used for visualizing the resulting 3D models. Since Autumn 1996, 3D-city models for these areas of the town where planning projects are under way are being created on a regular basis. Datasets from the Digital City Map The following GIS information of the digital city map is used by
GO-3DM:
• Terrain data. The first step in building the 3D-CM is modeling the terrain. GO-3DM computes a triangulation network from elevation points or an elevation raster. The Department for Surveying already has elevation data in a 20 x 20 m 2 raster for most parts of the town. In some more hilly areas a finer resolution will be needed. • Building blocks. In addition to the outline of a building its height has to be known to compute the lateral surfaces. Given this information simple blocks with flat or sloping roofs are generated. Some of this information already exists, the remainder will be obtained using photogrammetric data collection.
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benefits of using a 3D-city model. The applicability of the study's findings has been tested in a pilot project in an area north of the castle hill in Graz. The size of the project area is approximately 40 hectares, and includes about 50 buildings and the surrounding greenland, roads and a sports ground. Another goal of the pilot project was to test virtual reality and interactive modeling software for their potential applicability in urban planning.
Source Data from the Digital City Map The first step of the pilot project was the automatic generation of the 3D-CM. The dataset in DXF format selected from the digital city map (DCM) database for the project area is shown in Table 1. GO-3DM was used to automatically generate the corresponding 3D faces. The terrain in the project area is almost flat, so a plane surface was used instead of computing a terrain model. The result of this process is a 3D-model of the test area without textures (see Figure 3). Interactive Modeling and Real-Time Visualization In the next step, the images of the facades were added to the model. 50 photographs of the sides of the houses which look onto the main streets were taken and scanned. The program ALDUS PHOTOSTYLERTM was used to rectify and retouch them. The DXF-data generated by GO-3DM was then imported into 3DSTUDIOTM. Additional geometry for objects such as the net of the tennis court or the streetcar was defined in 3DSTUDIOTM.
FIGURE 3. Overview of the 3D-CM of " L n g e Game".
M. Ranzinger and G. Gleixner
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Table 1. Selected Data for the Project Area DXF layer
Used for
DACH SATTELDA FLACHDA HOEHENLI
root'lines and lateral surfaces ridgelines brealdines height of buildings: line with 2 points with height information (first point on lower edge of house, second point on upper edge of house) traffic ways (borders of roads and sidewalks) tracks of streetcar outlines of sporting grounds and parks trees (stored as circles, diameter gives approximate size of tree) roadmarks (pedestrian crossings, parking lots, etc.)
VKRFL SPLNLAY SONSTPKT GRUEN1 LEIT
The most time-consuming part is to attach the corresponding textures to each object. Since, until now, textures have not been stored in the DCM, this has to be done manually. A view of the test area with the textures added is given in Figure 4. The virtual reality application was performed on a Silicon Graphics ONYX Computer using the software packages MULTIGENTM of MultiGen Inc, USA for interactive modeling and VEGATM of Paradigm Inc, USA for real-time visualization. The 3D model of the existing buildings and the models of the three proposed building variants were imported from 3DSTUDIOTM into MULTIGEN TM, again using the DXF format. The structuring and reducing of the data for the real-time visualization was carried out in MULTIGENTM which offers a v a r i e t y of powerful functions for this task. To test the possibilities we added two examples for "level of details": Details of an object are only faded in when the viewer is approaching the object and gets closer than a predefined
FIGURE 4. Diagram showing the "Lange G m e " in detail.
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distance. This method was used for the net of the tennis court and for the windows in the roofs. The results o f the study were presented in a press conference, during which the real-time visualization and interactive editing o f one of the proposed buildings were demonstrated as well. Editing tasks such as adding one floor to a building or changing the color can be performed in real time. Urban planners, politicians and journalists were invited to walk through the virtual "Lange Gasse" on the screen.
OPERATIONAL PROCEDURE This section describes how the department for surveying in Graz plans to proceed with the introduction of the 3D-city model. In the long run the following process will be applied: Storage of the up-to date, valid data: in the Digital City Map database Editing of existing and adding of new source data (e.g. images of facades): in the DCM database Selection of the required urban area and the correspondingdatasets from the DCM database to generate the 3D-CM: on a project-by-projectbasis optional into Software package for interactive modeling and real- PC--CADsystem: for redevelopmentplans and during time visualization the early stages of a planning process Transfer of the CAD-model data into a rendering package for images and animations Transfer of the new, valid objects of the 3D-CM back into the DCM database F o r the process to run smoothly, the dataset has to be continually checked and updated and missing data has to be added. In the course of time, additional hardware and software will be acquired to enable more people in different urban planning boards to take advantage o f 3D-CM.
Data and Software for 3D-CM Creation In Table 2 the required data layers depending on the level o f detail of the 3D-CM are summed up.
Software for Automatic 3D Modeling Several pilot projects showed that GO-3DM generally meets the requirements of automatically generating a 3D-CM from the above source data. In the course of time, the following functionality will be added: (1)
(2)
GO-3DMwill read the data directly from the database o f the D C M without using the D X F format in between. Since the GIS used by the municipal department for surveying in Graz is SICAD-OPENTM (Siemens-Nixdorf, Germany), SICAD's G D B format will be one of the first formats to be supported. GO-3DMwill support several output formats besides DXF. Data from GO-3DM can then be directly loaded into the respective software packages for modeling and visualization.
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M. Ranzinger and G. Gleixner Table 2. Details of Required Data Layers
Needed for
Digital GIS dataset
Remarks
Base model • Digital terrain model, overlaid with contour lines or elevation points or required accuracy (or density of elevation raster points) depending on the terrain • Houses with flat or sloped roofs outlines and height of buildings
only • Generalized representation of traffic border between greenland and ways and greenland traffic ways
outlines should be connected (no holes) to facilitate automatic region building
trees
Block model • Based on the base model • Houses with roofs • Trees and special objects • More details • More details
existing data has to be checked and corrected; photogrammetric data collection in remaining areas
information on roofs: rooflines, ridgelines and breaklines as specified tree and bush cadastre outlines of sidewalks traffic ways (roads, tram, train)
Detailed model • Based on the block model • With photo-realistic textures • More typical details added • Use of standard textures and materials
special objects (e.g. lamps, poles, traffic-line markings) images of facades
data planned to be collected
will be collected on a project-byproject basis; periodical checks not planned standard symbols and textures (for library of standard symbols and walls, trees, traffic signs, etc.) textures is part of GO-3DM code for color and material for used instead of or additional to objects where no images e x i s t photographs
(3) An "inverse" interface to transfer newly constructed data from the 3D-CM back into the database of the DCM will be implemented. GO-3DM will also be used to improve the quality of the DCM database, because, especially, errors from photogrammetric data capture are easily detected when building or by inspecting the 3D-CM.
Software for Interactive Modeling T h e software MULTIGENTM tested i n the pilot project h a d a rather impressive set o f f u n c t i o n s w h i c h meet m o s t o f the r e q u i r e m e n t s set b y the u r b a n p l a n n e r s . I n the first phase, a less costly C A D package for the PC, such as AUTOCADTM f r o m A u t o d e s k , U S A , is sufficient for w o r k i n g with the block model.
Software for Real-Time Visualization T h e software for real-time visualization a n d the m o d e l i n g software m u s t use the same d a t a structure so n o a d d i t i o n a l d a t a conversions are necessary. This is the case with MULTIGENTM a n d VEGATM where d a t a edited in MULTIGENTM are i m m e d i a t e l y accessible b y V E G A TM .
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Presentation Software For the presentation of the planning results, the proposed objects should be viewed in all details from realistic viewing points. The results will be shown to many different people at different places. That is why the final presentations will not be done by using the real-time visualization, besides in most cases this would be too costly. Perspective plots, digital photographs and computer animations are much better suited for this purpose. They can be produced with a low-priced PC-based system like 3DSTUDIOTM.
PILOT PROJECTS Several pilot projects have been carried out until now on behalf of the city of Vienna and the department for city planning in Graz. They should show the feasibility and potential benefits of using a 3D-city model. A short description of two of them is given below.
KMbernes Viertel, Graz The "K/ilbemes Viertel" is a historic quarter along the river Mur in Graz. The project calls for the integration of a modem shopping and office center and a new access to the river. The first step was the automatic generation of the terrain, from the castle hill in the background down to the river. The 3D faces of the buildings and other objects were then automatically placed on the terrain model. The result of this step was a 3D model of the area without textures. In the next step, the images of the facades were added to the model. About 80 photographs of the sides of the houses which look onto the main streets were taken and scanned. The program ALDUS PHOTOSTYLERTM was used to rectify and retouch them. The D X F data generated by GO-3DM was then imported into 3DSTUDIOTM and the geometry of the proposed building added to it. Additional objects such as new trees or lamp posts were defined in 3DSTUDIOTM. The most time-consuming part is to attach the corresponding textures to each object. Since, until now, textures have not been stored in the digital city map, this has to be done manually. The resulting video compares the computer animation of the proposed building with historic drawings of the area and takes the viewer on a stroll along the river and over the newly modeled bridge. A view of the resulting model of the proposed building and its surroundings is given in Figure 5.
"Nordbahnhor', A Railway Station Comes Alive, Vienna The aim of the project is to reuse part of a railway station as a new area for a living, shopping and business center. Most of the railway station is not used for trains any more so it is interesting to show how the future development of this part of Vienna could look in some years. Figure 6 shows the new planned buildings and buildings which already exist. The surrounding is shown as a 2D map. Just some very important buildings are modeled in 3D (see Figure 7).
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FIGURE 5. KYdbernes Viertel with proposed shopping center.
The work was done together with the staff of the city of Vienna. Many thanks to them. They have now been using GO-3DM for about 1.5 years and have performed a lot of projects on their own.
FIGURE6. Overviewof the
area "Nordbahnhof",
Vienna.
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FIGURE 7. Proposed redevelopment of the area around "NordbAhnhor',Vienna.
CONCLUSION Innovative techniques for the visualization and presentation of architecture and more efficient tools for planners and architects have evolved from the current progress in information technology and the improvements in computer hardware and software. The exploitation of these techniques has only just started in Austria - - but there are more and more people from different application areas getting interested. Especially, 3D city planning offers many advantages to citizens and planners alike: • Citizens get more involved in planning processes once they really see what is going to be built - - and they accept changes in their neighborhood more easily. • Planners like it because they can explain their ideas much more fully. They can speed up the planning process and are still able to test more variants. • Politicians feel more secure about their decisions if they have visualized all aspects of a new project.
Comput., Environ.and Urban Systems,Vol. 21, No. 2, pp. 159-173, 1997 © 1998ElsevierScienceLtd. All rights reserved Printed in Great Britain 0198-9715/98 $19.00 + 0.00 PII: S0198-9715(97)10005-9
GIS DATASETS FOR 3D URBAN PLANNING Monika Ranzinger and GOnther Gleixner ~ GRINTEC GesmbH, Gesellschaft for Graphische, Maiffredygasse 4/11, A-8010 Graz, Austria ABSTRACT. For decades urban planning was done by drawing plans and building elaborate models from wood and pasteboard. The Austrian Cities of Graz and Vienna are demonstrating that this is a thing of the past - - its threedimensional (3D) computer simulations derived from information of the digital city map are revolutionizing the planning process. The paper deals with the feasibility and potential benefits of a 3D-city model and covers the following topics:
(1) What is a 3D-city model? (2) What is it ased for? (3) Which data is needed for a 3D-city model and where is it derived from? (4) How can a 3D-city model be generated on a regular, operational basis? Results of projects carried out in Graz and Vienna will be shown to demonstrate the operational applicability of a 3D-city model. © 1998 Elsevier
Science Ltd. All rights reserved
INTRODUCTION F o r decades urban planners and architects have used drawings and elaborate wood and pasteboard models to convey their ideas.
Conventional Visualization Techniques Until now mainly non-digital presentation forms have been used in architecture and urban planning: • Model. Based on the drawings of the architect, a wood or pasteboard model of the
building is made. The disadvantage of this technique is that a good model with all realistic details is very expensive. There is also no possibility to see the building in a realistic perspective and making changes to the model is rather complicated and time consuming. 1Tel: 43 316 383706; Fax: 43 316 8370620. 159
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• Perspective drawings. Perspective views of the building are created either by hand or
by means of computer software. Normally only the vertices of a building are constructed. Details such as windows, doors and the surroundings are sketched freehand. The aesthetic impression depends very much on the skills of the draftsman. • Photomontage. A photograph of the building site is used as background for a perspective drawing. By including the actual vicinity of the building this technique gives a more realistic impression. All these methods generally have some drawbacks as regards realistic impression, easy adaption to changes or simple comparison between different variants. As citizens demand more influence in planning processes, new computer-based methods like three-dimensional (3D) computer simulations and animations are called for. We at GRINTEC have long-time experience in applying different digital techniques to "make the future visible". Motivation The origins of our work in this field date back more than ten years. Our first project, which was carried out on behalf of the municipal department for urban planning in Graz, was a computer animation showing different architectural proposals for a new building on F/irberplatz. The surrounding buildings and the simulated camera motion remained unchanged, with the proposed buildings faded in one by one. Existing and new buildings were only depicted as simple blocks with roofs, the display of materials like glass or wood did not look good and took hours to compute. Effects such as shadows and reflections or additional objects such as trees and lamps were not used at all. Compared with today's technical possibilities it was rather low-level and very costly hardware was needed. Just the same, we became fascinated by the new possibilities and developed many ideas for improving the results and reducing the effort and expense for data acquisition. In 1989, when the required hardware was available, we translated one of these ideas into reality: To overlay a standard video film of the building site with computer-generated images of the building. The first operational version of the resulting software package moveX was completed by mid-1991. In the same year a video film produced with moveX won the video and slide contest of Eurographics '91 and was given an award at the International Prix Ars Electronica in Linz.
VIDEO MONTAGE WITH MOVEX moveX - - a video montage system - - combines the advantages of the photomontage technique and computer animation. A video f i l l of the building site is overlayed with computer-generated images of the proposed buildings - - thus the realistic surroundings and the 3D impression of the f i l l are maintained. Source data for moveX simply consists of a video of the building site and the plan or CAD data of the proposed building - - or buildings if different building designs will be visualized, moveX computes, for each frame of the video, the corresponding perspective of
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the new building and overlays the video frame with the computed image. For the viewer, the resulting film gives the impression of the new object already being in its position.
Working with moveX For creating a video with moveX, the following steps have to be performed.
Creation of the Source Video The first step is to create a video film of the building site. Depending on the size of the building project, this can be done by walking round or from a car or by using a helicopter. Computer Aided Design Construction of the Building Additional to the CAD model, the colors and materials of the new building have to be defined. Calculation of Video Parameters A standard video recorder stores 25 frames or 50 half-frames per second. In order to overlay a video film with computer-generated images: • the exact camera position, • the viewing direction, and • the zoom adjustment for every frame of the film have to be known. moveX reconstructs these parameters from the video frames by using "passpoints". Passpoints are special image points with known world coordinates. They should be easily distinguishable from the background and well distributed in the frame and must not lie in one plane. At least five independent passpoints for each frame are needed for calculating the camera parameters. Since the positions of the passpoints in all frames of the video film have to be known to calculate the camera movement, it would take too long to measure them manually. That is why passpoints are tracked automatically by applying pattern recognition and making use of the fact that the position of a passpoint does not change very much between consecutive frames. Thus passpoints have to be manually identified only in the frame in which they appear for the first time. For this process, all images of the video film are digitized and stored by means of special hardware.
Masking Objects such as trees or cars which should remain in front of the new object must not be overlaid by the image of the new object. In these cases the method of masking is applied. Only uncomplicated objects permit one to apply 3D masks, where we add a 3D representation of the object to the CAD description of the planned building. This is quite efficient because the position of the mask has to be specified only once. Complex objects such as cars are difficult to construct with CAD, therefore we manually digitize a 2D mask on screen. This has to be done every fifth to tenth video image. The 2D masks for the frames in between are interpolated using a third-degree polynomial.
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Both 3D and 2D masks give optically satisfying results. Sometimes we have to apply another technique if the objects to be masked are very complex. In this case we create binary mask images. To find, for example, branches of a tree, we use the same classification techniques as for passpoint recognition.
Rendering of the New Building As a result of the previous steps we know all the camera parameters necessary to compute the corresponding perspective view of the new building for every frame of the video film. Each digitized image of the video film is now overlaid with data from the computer-generated images of the building. The resulting images are again recorded on video tape.
"'Parkshop (14"; Vienna One of our first moveX projects was the visualization of a planned parkshop with a shopping center, offices and apartments on behalf of municipal departments for urban planning and for data processing in Vienna. "Parkhaus U4" is situated near an underground station of line 4. The already existing parking garage had to be incorporated into the new building design. Different video sequences approaching and passing the future building by car were recorded. To get an overview of the whole area a pan was filmed from the roof of the hotel directly opposite. Filming a building which does not yet exist is not as easy as it may seem and takes a lot of imagination. The cameraman has to estimate the dimensions of the building to chose suitable views and details. For "Parkshop U4" we filmed a lot of reserve footage to be sure that all required sequences were included. As we did not take care not to include foreground objects in our video, we ended up with quite a lot of masking work to do. We had to mask out cars, street lamps, traffic signs and bushes. We used 2D masks for cars, street lamps and traffic signs and binary masks for bushes. For calculating the camera parameters of the video we used streetlamps, windows of buildings, traffic signs, zebra crossings and other easily identifiable objects as passpoints. The world coordinates of some of these passpoints could be selected from the geographical information system (GIS) of Vienna, others had to be geodetically measured. In the first stage we created a film sequence of about 45 seconds which showed the new building in detail from different perspectives. This film was reviewed by the architect and the staff of the municipal departments. Some changes in the building design resulted from this meeting. Afterwards, the final version of the video was produced. It was computed on a SGI Personal IRIS using our own rendering software, the average computing time for one frame was about 3 minutes.
Administration Building, Deutschlandsberg, Styrla The animation of a planned administration building in a district town in Styria was done to inform the citizens in the vicinity of the proposed development. We encountered several problems when generating the source video: • From two sides the building site was not accessible, so these parts could only be filmed from the bird's-eye view. We used the crane on the neighboring site to shoot this video footage.
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• Adjoining sites were already under construction, which leaves an impression of incompleteness in the resulting video. For the rendering of the new building some nice effects were used. The material for most parts of the facades was planned to be glass, which is why we also filmed the houses across the street and used these images for the reflections in the glass facades. Part of the computer animation is a simulation of the interior. The facades of the houses across the street are used in this sequence to give a realistic view when one looks out of the office windows.
Advantages and Disadvantages of Video Montage The technique of video montage is especially well suited: • for the evaluation of different variants of a planned building, • for development projects, where the surrounding is of critical importance (e.g. in old town centers), and • because videos can be easily copied and can be shown virtually everywhere. Video montage is not the right technique to use: • if adjacent sites or the site itself are already under construction, • if there will be major changes in the surrounding terrain or a redesign of a whole area, and • if the view of the future building is obstructed by too many other objects, which remain in the foreground and have to be masked.
3D-CITY MODEL To be able to make changes to the surrounding of a proposed building and view the results from any viewpoint, one needs a 3D model not only of the new building but of the whole townscape. A 3D-city model (3D-CM) is a special computer representation of all fixed objects (buildings, vegetation, traffic ways and waterways) within a town. It contains all the information necessary to view each object from all sides and the main characteristics to make it recognizable. It is sort of a CAD model of the whole town. One of several pilot projects to test the applicability and potential benefits of a 3D-city model was the computer animation of the proposed "New Jakominiplatz" (Figure 1), which was produced on behalf of the municipal department for urban planning.
Project Jakominiplatz The animation shows Jakominiplatz, the busiest junction for public transport in Graz, as it will appear in Autumn 1996 after two years of rebuilding. The video takes the viewer on a walk around the new square, highlighting the different features of the architectural scheme as one walks along. Finally, one takes a virtual ride on the tram which is already running on its future rails. The layout of the source model for Jakominiplatz was taken from the digital city map. By using plans and photogrammetric interpretation a wire-frame model of the existing objects was generated. For the buildings to be identifiable, mere blocks with roofs are not
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FIGURE 1. Image of the
new
Jakominlplatz.
sufficient. We took a photograph of the fronts of all houses which look onto the square, scanned and rectified them and "glued" them digitally onto the facades of our digital model. Finally, CAD data of the proposed new objects was added to the model. We estimated that almost two thirds of the working time for the animation would have been saved if a 3D model of the Jakominiplatz had already existed and could have been used.
Applications of 3D-City Models 3D-city models can be used in many fields of urban planning: • Analysis o f the present situation. 3D visualizations give a better impression of the surrounding than 2D maps and help pinpoint problem areas where something needs to be done. • Planning and control. Interactive planning of buildings enables planners to show different stages of redevelopment. They can simulate redevelopment plans within seconds in order to compare the new plans with the virtual world around them. Different types of 3D products are necessary during the planning stage. Planners can start with a rather abstract model of the surroundings and add more and more details as the planning process evolves. There are many applications for other urban planning boards as well, e.g. road planners can review traffic signs by controlling whether they can be seen from all directions. • Decision support. Different designs of buildings can be compared directly in their future surrounding, the decision-making process is quicker and more efficient. • P r e s e n t a t i o n . Using the information stored in the 3D-CM documentations, perspective drawings, digital photographs and films of the present townscape overlaid with proposed buildings can be produced. Even virtual worlds can be created,
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enabling citizens to walk through future urban areas and have proposed changes explained to them.
Basic Information for the 3D-City Model Until now 3D-CAD has mostly been used for modeling single buildings or blocks of buildings. Since it takes quite an amount of interactive work to input the data, a 3D-model of a whole town seemed to be too costly. But much of the information necessary for a 3DCM already exist in the digital city maps. Vienna and smaller Austrian cities such as Graz or Linz started to build databases for the digital city map in the 1980s. By now they have stored all the basic layers, such as topography, road network, parcels, houses, parks and grassland, and have collected a lot of additional information as well. To collect or store these data once again in a different format for a 3D model would be inefficient. That is why GRINTEC developed the software package C,O-3DM (GIS objects to 3D models) which automatically converts GIS data into a 3D model. C,O-3DMcurrently reads D X F data and generates D X F 3D faces or 3D triangles. Figure 2 gives an overview of GO3DM. When the city of Vienna acquired GO-3DMin 1995, detailed specifications for collecting, structuring and storing all information necessary for the 3D-CM were laid down. These include information on the height of objects, roof-types or images of facades. The information is all going to be stored and managed in the database of the "Wiener Mehrzweckkarte" (Vienna multipurpose map, MZK). Thus the GIS will remain the central tool for data storage and data management. Changes made in the 3D model will not be saved over a longer period, instead the corresponding information will be edited in the M Z K database. GO-3DM and the specifications for data capture - - photogrammetry is used to collect heights and roof lines - - have already been tested in several new pilot projects and have achieved good results. Only minimal editing - - mostly to correct complicated roofs - was required for the automatically generated 3D model. By using this method, the city of Vienna can go on using the M Z K for its usual applications and have the base data ready for the 3D-CM. Currently about 20 employees of the city of Vienna are trained in the use of GO-3DM and of 3DSTUDIOTM, the software used for visualizing the resulting 3D models. Since Autumn 1996, 3D-city models for these areas of the town where planning projects are under way are being created on a regular basis. Datasets from the Digital City Map The following GIS information of the digital city map is used by
GO-3DM:
• Terrain data. The first step in building the 3D-CM is modeling the terrain. GO-3DM computes a triangulation network from elevation points or an elevation raster. The Department for Surveying already has elevation data in a 20 x 20 m 2 raster for most parts of the town. In some more hilly areas a finer resolution will be needed. • Building blocks. In addition to the outline of a building its height has to be known to compute the lateral surfaces. Given this information simple blocks with flat or sloping roofs are generated. Some of this information already exists, the remainder will be obtained using photogrammetric data collection.
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benefits of using a 3D-city model. The applicability of the study's findings has been tested in a pilot project in an area north of the castle hill in Graz. The size of the project area is approximately 40 hectares, and includes about 50 buildings and the surrounding greenland, roads and a sports ground. Another goal of the pilot project was to test virtual reality and interactive modeling software for their potential applicability in urban planning.
Source Data from the Digital City Map The first step of the pilot project was the automatic generation of the 3D-CM. The dataset in DXF format selected from the digital city map (DCM) database for the project area is shown in Table 1. GO-3DM was used to automatically generate the corresponding 3D faces. The terrain in the project area is almost flat, so a plane surface was used instead of computing a terrain model. The result of this process is a 3D-model of the test area without textures (see Figure 3). Interactive Modeling and Real-Time Visualization In the next step, the images of the facades were added to the model. 50 photographs of the sides of the houses which look onto the main streets were taken and scanned. The program ALDUS PHOTOSTYLERTM was used to rectify and retouch them. The DXF-data generated by GO-3DM was then imported into 3DSTUDIOTM. Additional geometry for objects such as the net of the tennis court or the streetcar was defined in 3DSTUDIOTM.
FIGURE 3. Overview of the 3D-CM of " L n g e Game".
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Table 1. Selected Data for the Project Area DXF layer
Used for
DACH SATTELDA FLACHDA HOEHENLI
root'lines and lateral surfaces ridgelines brealdines height of buildings: line with 2 points with height information (first point on lower edge of house, second point on upper edge of house) traffic ways (borders of roads and sidewalks) tracks of streetcar outlines of sporting grounds and parks trees (stored as circles, diameter gives approximate size of tree) roadmarks (pedestrian crossings, parking lots, etc.)
VKRFL SPLNLAY SONSTPKT GRUEN1 LEIT
The most time-consuming part is to attach the corresponding textures to each object. Since, until now, textures have not been stored in the DCM, this has to be done manually. A view of the test area with the textures added is given in Figure 4. The virtual reality application was performed on a Silicon Graphics ONYX Computer using the software packages MULTIGENTM of MultiGen Inc, USA for interactive modeling and VEGATM of Paradigm Inc, USA for real-time visualization. The 3D model of the existing buildings and the models of the three proposed building variants were imported from 3DSTUDIOTM into MULTIGEN TM, again using the DXF format. The structuring and reducing of the data for the real-time visualization was carried out in MULTIGENTM which offers a v a r i e t y of powerful functions for this task. To test the possibilities we added two examples for "level of details": Details of an object are only faded in when the viewer is approaching the object and gets closer than a predefined
FIGURE 4. Diagram showing the "Lange G m e " in detail.
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distance. This method was used for the net of the tennis court and for the windows in the roofs. The results o f the study were presented in a press conference, during which the real-time visualization and interactive editing o f one of the proposed buildings were demonstrated as well. Editing tasks such as adding one floor to a building or changing the color can be performed in real time. Urban planners, politicians and journalists were invited to walk through the virtual "Lange Gasse" on the screen.
OPERATIONAL PROCEDURE This section describes how the department for surveying in Graz plans to proceed with the introduction of the 3D-city model. In the long run the following process will be applied: Storage of the up-to date, valid data: in the Digital City Map database Editing of existing and adding of new source data (e.g. images of facades): in the DCM database Selection of the required urban area and the correspondingdatasets from the DCM database to generate the 3D-CM: on a project-by-projectbasis optional into Software package for interactive modeling and real- PC--CADsystem: for redevelopmentplans and during time visualization the early stages of a planning process Transfer of the CAD-model data into a rendering package for images and animations Transfer of the new, valid objects of the 3D-CM back into the DCM database F o r the process to run smoothly, the dataset has to be continually checked and updated and missing data has to be added. In the course of time, additional hardware and software will be acquired to enable more people in different urban planning boards to take advantage o f 3D-CM.
Data and Software for 3D-CM Creation In Table 2 the required data layers depending on the level o f detail of the 3D-CM are summed up.
Software for Automatic 3D Modeling Several pilot projects showed that GO-3DM generally meets the requirements of automatically generating a 3D-CM from the above source data. In the course of time, the following functionality will be added: (1)
(2)
GO-3DMwill read the data directly from the database o f the D C M without using the D X F format in between. Since the GIS used by the municipal department for surveying in Graz is SICAD-OPENTM (Siemens-Nixdorf, Germany), SICAD's G D B format will be one of the first formats to be supported. GO-3DMwill support several output formats besides DXF. Data from GO-3DM can then be directly loaded into the respective software packages for modeling and visualization.
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M. Ranzinger and G. Gleixner Table 2. Details of Required Data Layers
Needed for
Digital GIS dataset
Remarks
Base model • Digital terrain model, overlaid with contour lines or elevation points or required accuracy (or density of elevation raster points) depending on the terrain • Houses with flat or sloped roofs outlines and height of buildings
only • Generalized representation of traffic border between greenland and ways and greenland traffic ways
outlines should be connected (no holes) to facilitate automatic region building
trees
Block model • Based on the base model • Houses with roofs • Trees and special objects • More details • More details
existing data has to be checked and corrected; photogrammetric data collection in remaining areas
information on roofs: rooflines, ridgelines and breaklines as specified tree and bush cadastre outlines of sidewalks traffic ways (roads, tram, train)
Detailed model • Based on the block model • With photo-realistic textures • More typical details added • Use of standard textures and materials
special objects (e.g. lamps, poles, traffic-line markings) images of facades
data planned to be collected
will be collected on a project-byproject basis; periodical checks not planned standard symbols and textures (for library of standard symbols and walls, trees, traffic signs, etc.) textures is part of GO-3DM code for color and material for used instead of or additional to objects where no images e x i s t photographs
(3) An "inverse" interface to transfer newly constructed data from the 3D-CM back into the database of the DCM will be implemented. GO-3DM will also be used to improve the quality of the DCM database, because, especially, errors from photogrammetric data capture are easily detected when building or by inspecting the 3D-CM.
Software for Interactive Modeling T h e software MULTIGENTM tested i n the pilot project h a d a rather impressive set o f f u n c t i o n s w h i c h meet m o s t o f the r e q u i r e m e n t s set b y the u r b a n p l a n n e r s . I n the first phase, a less costly C A D package for the PC, such as AUTOCADTM f r o m A u t o d e s k , U S A , is sufficient for w o r k i n g with the block model.
Software for Real-Time Visualization T h e software for real-time visualization a n d the m o d e l i n g software m u s t use the same d a t a structure so n o a d d i t i o n a l d a t a conversions are necessary. This is the case with MULTIGENTM a n d VEGATM where d a t a edited in MULTIGENTM are i m m e d i a t e l y accessible b y V E G A TM .
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Presentation Software For the presentation of the planning results, the proposed objects should be viewed in all details from realistic viewing points. The results will be shown to many different people at different places. That is why the final presentations will not be done by using the real-time visualization, besides in most cases this would be too costly. Perspective plots, digital photographs and computer animations are much better suited for this purpose. They can be produced with a low-priced PC-based system like 3DSTUDIOTM.
PILOT PROJECTS Several pilot projects have been carried out until now on behalf of the city of Vienna and the department for city planning in Graz. They should show the feasibility and potential benefits of using a 3D-city model. A short description of two of them is given below.
KMbernes Viertel, Graz The "K/ilbemes Viertel" is a historic quarter along the river Mur in Graz. The project calls for the integration of a modem shopping and office center and a new access to the river. The first step was the automatic generation of the terrain, from the castle hill in the background down to the river. The 3D faces of the buildings and other objects were then automatically placed on the terrain model. The result of this step was a 3D model of the area without textures. In the next step, the images of the facades were added to the model. About 80 photographs of the sides of the houses which look onto the main streets were taken and scanned. The program ALDUS PHOTOSTYLERTM was used to rectify and retouch them. The D X F data generated by GO-3DM was then imported into 3DSTUDIOTM and the geometry of the proposed building added to it. Additional objects such as new trees or lamp posts were defined in 3DSTUDIOTM. The most time-consuming part is to attach the corresponding textures to each object. Since, until now, textures have not been stored in the digital city map, this has to be done manually. The resulting video compares the computer animation of the proposed building with historic drawings of the area and takes the viewer on a stroll along the river and over the newly modeled bridge. A view of the resulting model of the proposed building and its surroundings is given in Figure 5.
"Nordbahnhor', A Railway Station Comes Alive, Vienna The aim of the project is to reuse part of a railway station as a new area for a living, shopping and business center. Most of the railway station is not used for trains any more so it is interesting to show how the future development of this part of Vienna could look in some years. Figure 6 shows the new planned buildings and buildings which already exist. The surrounding is shown as a 2D map. Just some very important buildings are modeled in 3D (see Figure 7).
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FIGURE 5. KYdbernes Viertel with proposed shopping center.
The work was done together with the staff of the city of Vienna. Many thanks to them. They have now been using GO-3DM for about 1.5 years and have performed a lot of projects on their own.
FIGURE6. Overviewof the
area "Nordbahnhof",
Vienna.
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FIGURE 7. Proposed redevelopment of the area around "NordbAhnhor',Vienna.
CONCLUSION Innovative techniques for the visualization and presentation of architecture and more efficient tools for planners and architects have evolved from the current progress in information technology and the improvements in computer hardware and software. The exploitation of these techniques has only just started in Austria - - but there are more and more people from different application areas getting interested. Especially, 3D city planning offers many advantages to citizens and planners alike: • Citizens get more involved in planning processes once they really see what is going to be built - - and they accept changes in their neighborhood more easily. • Planners like it because they can explain their ideas much more fully. They can speed up the planning process and are still able to test more variants. • Politicians feel more secure about their decisions if they have visualized all aspects of a new project.