Animation and visualization in design of a new transportation system in existing urban environment using GIS and Virtual Reality

ABSTRACT

A virtual city was built to visualize how an aerial cableway may solve an increasing demand for public transportation in the city of Göteborg (Gothenburg). This model was made at Chalmers University of Technology, school of Architecture and was optimized for a 3D Cube environment.

The 3D model was created using Arc/Info 7.2 including the Grid submodul, ArcView GIS 3.1 and TerraVista 2.1 from Terrex Inc. (an Esri partner). The latter was used to generate the virtual reality model. The 3D Cube was used to present the scene in virtual reality, and makes it possible to take a tour with the virtual cableway.

It is believed that the integration of GIS and VR technology will become an indispensable tool for planners in the near future. A 3D Cube makes it possible to test and experience various planning alternatives, especially in an urban environment but also in other planning situations.

Keywords: GIS, Virtual Reality, VR, Aerial cableway, 3D-Cube, City 3D model

1. Introduction

The map in Figure 1 shows the existing and planned locations of Universities in Göteborg. The Göta Älv River separates the town in two parts. One of the new big knowledge nodes has started to grow on the north shore while the bulk of the existing University nodes are located south of the river. The nationally important transports on the river must not be disturbed and it needs headroom of at least 45 meters. New "bridging" has to be constructed adding accessibility to the existing tunnel and two bridges in the central area.

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Figure 1. The university locations in the center of Göteborg result in a demand of a good transportation system in the future.

2. A transport system proposal

The passenger capacity must exceed the level specified to other public transport systems, i.e. 2,000 persons per hour. With a great number of cablecars seating six persons will satisfy this requirement. Top capacity is calculated to be 4,000 persons per hour. With a car speed of 5 m/s the travelling time between the two nodes, main campus of Chalmers and Chalmers Lindholmen, will be just above 15 minutes, independent of when the trip starts (Figure 2). The system is specified to stand for a wind speed of 28 m/s, equivalent to the existing bridges.

The cableway system will most likely be leveled high to reduce the number of pylons and when crossing the river exceed the required headroom of 45 meters. The transport system will if possible operate automatically to a great extent.

To design and implement a new transport system in an existing urban environment requires extensive information and establishing support for the idea. The possibility to study and experience the system in a virtual reality gives unique prospects for agents to influence and participate in the design process. It is an example how new technology may be crucial for the development and implementation this type of innovative proposals.

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Figure 2. The proposal to the aerial cableway connects the universities.

3. Creating the 3D scene

The input data has been imported to Arc/Info and was prepared in order to suit the model generator, TerraVista. The virtual reality (VR) model was adapted for presentation in a 3D Cube. This device is a room with the dimensions 3x3x3 meters, having 5 projectors that display up to 50 million polygons per second on the walls and on the floor (Figure 3). A 64-processor Silicon Graphics Onyx machine with high potential graphics equipment drives the 3D Cube.

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Figure 3. A Silicon Graphics Onyx II Computer, equipped with three separated graphic pipes run all five projectors. Each pipe has two graphic channels thus enabling the system to run six projectors. Each projector shows the image in stereo, so when wearing synchronized "Shutter Glasses" the viewer gets a completely immersive stereoscopic view of the world. An electromagnetic field in the 3D-CUBE corresponds with sensors on the person, to track his or her position. Certain "peripherals" such as gloves and pointers then make interaction with the environment possible. The separately running Lake sound system simulates distance, direction and character of the sound to give a complete illusion.

The TerraVista software version 2.1 (November 1999) was not ready to create 3D buildings out of 2D polygons GIS data. The partnership with Esri had however the intention to develop better treatment of 2D GIS data, even for the buildings data type. An extension, Automatic Culture Generator (ACG), was under development and for this project we had the opportunity to use an early beta version to be able to rise the buildings to the height above ground, which was stored as an attribute to these polygons.

4. Source data

-Digital Terrain Model (DTM), from points in a 12 meter grid (ASCII file).
-Roof lines having elevation value (AutoCad vector file).
-Water polygons without elevation (Shape file).
-Streets and railways without elevation (Shape file).
-Orthophotos, resolution: 0.25 meter (georeferenced TIFF image).
-Aerial cableway, 3D linear features digitized in ArcView GIS (3D Shape file).

In our situation we had to focus on a generalized scene that should cover a big part of the city. The reason for this was that the objective was to create a possibility to experience the aerial cableway from a virtual journey within the cablecar it self, as well as watch it from any optional location.

The 3D model was built in a manner so that the buildings had flat roofs and random textures on the outside walls. The shapes of the buildings were limited to have flat roofs because their origin of 2D GIS data. That means that a roof as easy as a rectangle in shape is build as a box. The height of the box is determined from the roof's height value and calculated from it's lowest point in the terrain.

The TerraVista software is very tolerant software regarding its treatment of input data and how it should appear in the terrain. There was however some modifications needed to be able to put the buildings on the terrain.

The principle used is to drape features on the digital terrain model to produce 3D plots (just as was possible in early version of Arcplot) . Some features such as buildings must have relative heights, which means height above ground level, while other features such as the cableway (3D linear data) must have absolute heights. Streetlines were widened to one width for all, because the real width was not in the database. These features were draped on the DTM without any special respect to horizontal appearance of the streets, which however is possible. The preparation of the datasets included:

1. In Arc/Info, the DTM is imported to a Grid and exported as an ASCII Grid file, which can be imported to TerraVista.

2. Buildings had to be built from roof polygons, and polygons had to be created from the rooflines. Arc/Info's CLEAN command produces the polygons very easy. Then the roof heights were estimated from one of the lines describing the roof. Buildings in Sweden sometimes have flat roofs, but (unfortunately in this case) this is not the prevailing type. There are also many smaller machine rooms for fans, elevators etc. on the roofs that must be removed. The roof heights were retrieved from the lowest line around the roof. This gave us the walls in real heights and most buildings have a very realistic size appearance. There are of course some buildings with large non-flat roofs that has to be modified in the 3D model, in order to recognized. These buildings are often churches. One particular building close to the cableway, the Fish Church ("Feskekörka" in the local dialect) which is a fish market in a well known building, needed to look real (Figure 4). Elevation values had to be recalculated from absolute heights to relative heights above ground. The relative heights were calculated from the absolute heights minus the lowest ground level, which was found in the DTM Grid. The roofs are cleaned from all features but tall chimneys. The tall buildings and chimneys are not common in our city, but is very important as landmarks when moving in the model or viewing a 2D perspective of the city. Adjacent roof polygons were dissolved if their height was approximately the same. This is an important step to do, because when the 3D buildings are build, all linear features get a wall down to the ground and the number of such walls must be minimized to increase performance when traveling in the VR environment in the 3D Cube. All the roof preparations were done in Arc/Info. Then the roof polygons were converted to shape files.

3. A water polygon does not need any elevation values. TerraVista makes water surfaces from the lowest elevation found in the DTM in the area that are occupied by the water polygons.

4. Streets and railways are draped on the DTM. A uniform width was assigned to these features. In this operation, it would have been preferable if a width attribute had been available.

5. The aerial cableway was digitized in ArcView GIS as a 3D linear feature, having elevation values of absolute heights.

When the 3D scene is build, you can work with single objects in 3D-design software, such as Multigen Creator [Infoga Referens]. This was important here to be able to refine the model. Building the city in the way we did, gave us a huge model in very short production time, but there are no details like phototextures on the walls or modeled complex roofs.

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Figure 4. The well-known Fish Church is a fishmarket. More detail needs to be assigned to such special landmarks. Even if most buildings are generalized to boxes, the model will become much more realistic for a viewer if certain features look relatively "real".

5. Conclusions

7. Acknowledgements

References

Reneland, M and Hagson, A (1996). PRT System in Swedish Towns - Conditions given by and consequences for town structure and townscape

Terrex Terrain Experts Inc. (1999). TerraVista User's Manual V2.0

Internet

www.arch.chalmers.se

www.medialab.chalmers.se

Jan Bjurström
Department of Urban traffic and Land use
School of Architecture
Chalmers University of Technology
SE-412 96 Göteborg, Sweden
phone: +46 - (0)31 772 2429
fax: +46 - (0)31 772 2394
e-mail: jan.bjurstrom@arch.chalmers.se

Jonas Tornberg
Department of Urban traffic and Land use
School of Architecture
Chalmers University of Technology
SE-412 96 Göteborg, Sweden
phone: +46 - (0)31 772 2433
fax: +46 - (0)31 772 2394
e-mail: jonas@arch.chalmers.se

Presented by Jonas Tornberg, M.Sc.C.E at the 2000 Esri User Conference

Chalmers University of Technology
SE-412 96 Göteborg, Sweden
Phone: +46 - (0)31 772 1000
Fax: +46 - (0)31 772 3872