Interactive generation of cities for real-time applications

Cells created from the division of the city by the primary road network form units of area upon which the secondary road generation component can operate. A technique similar to that used in the CityEngine [2001] based on L-systems can be applied for secondary road generation. The algorithm will be applied within each cell to create roads that service the land area by providing access to and from the primary road network. Global and local parameters for each cell can control the operation of the secondary road generation. Our system aims to provide an environment in which these parameters are easily accessible and a live preview is available. Buildings can be placed on the lots created by the enclosed regions from the secondary road generation. Building geometry will be constructed using L-systems taking several different building usage types into account including commercial, industrial, and residential with these usage types either stochastically assigned by the system or explicitly assigned by the user via the interactive interface. Real-Time rendering is possible in our design via the provision of a number of optimization features: city cell paging, level of detail and real-time geometry generation. City cell paging is a concept similar to terrain paging systems, the primary road network forms a skeleton for the city containing the generation parameters for the entire city partitioned into cells. The secondary road networks within each cell are paged andcan be pre-emptively generated and loaded on demand. Building structures stored as L-system strings can be parsed at run time to generate geometry. This provides a substantial reduction in memory usage by storing simple strings rather than complex geometry and also enables variants of buildings to be constructed depending on the parameters used for instantiation. A range dependent level of detail implementation can be constructed by including a parameter to specify the distance from camera to building and adjust the number of L-system iterations used accordingly. The implementation of our design is currently in progress. The interactive application has been built and the primary road generation component is complete, we expect to complete the final stages of the prototype in the next 6-8 months.