Virtual Cities

------------- Introduction

This project aims to explore new interaction possibilities with virtual cities, including, for example, the changing of the urban geometry or the navigation within the city.

We performed our research using a VRML model of Lisbon, which we kindly obtained from Jose Dionisio, Instituto Superior Tecnico, DEM/SAE, Lisbon.

The VR software "VirtualDesign II" by Vrcom running under Linux is used for visualization.

The software can be extended by plug-ins, carrying out the interaction with the virtual city.

As input devices a spacemouse, a data glove (Immersion), a head-mounted display (Virtual Research), and a electromagnetic tracking system (Polhemus) are used.

See below for a few videos

------------- Plug-Ins:


With the plug-in lineup, new objects can be integrated in the scene and can be placed along a straight line. Therefore, first of all a ray is sent from the virtual hand into the scene. The first object is placed on the point of intersection of the ray and the terrain.

More objects are created by moving the ray. This extends the line on the terrain, and the plugin dynamically adds more objects along the line. It is possible to vary the number of objects interactively, allowing for example to quickly equip a road with streetlights.

The objects are automatically adapted to the height of the surroundings.

With the plug-in findpath, the shortest path within a city can be calculated and visualized.

As virtual city models generally don't include any information about the course of the streets, we extract a street graph from the VRML geometry.

To that end, the floor plans of the houses are calculated first (red).
Second, a generalized Voronoi diagram is computed from these 2D polygons with the help of the software VRONI. (blue)
The result is a coherent graph, representing the course of the streets. Using Dijkstra's algorithm, which has been implemented with a Fibonacci-Heap from Shane Saunders, the shortest path can be searched in this graph (green).
The way viewed from the street. The green balls mark the Voronoi nodes.
The plug-in "multimove" is used to change the geometry of the city.

A house is marked by a ray and moves along the point of intersection of the ray and the terrain.

It is possible to select more than one house. These houses then move along the ray, depending on their distance to the firstly selected house.

A relative placement of the selected houses is also possible.

Consequently, the buildings are able to approach each other or to remove from each other -- better demonstrated in the video (below).

------------- Videos:

Lineup (also showing the interaction utilizing the above mentioned VR devices. 5 MB).

Findpath (5 MB).

Multimove (5 MB).

Gabriel Zachmann
Last modified: Sat Sep 10 16:00:44 MDT 2005