Procedural Urban Streets in Real-Time Stefan Greuter * Nigel Stewart † Geoff Leach ‡ Abstract Cities are popular settings for computer game levels and flight simulators. The creation of a virtual city model poses a distinct set of chal- lenges to the designers. The design of a virtual city often starts with the creation of a road net- work. The road network subdivides the virtual space into smaller areas that are surrounded by streets. These areas can be further subdivided to create areas for buildings, parklands etc. We present a procedural approach to generate urban street networks for virtual cities in real-time on desktop computers with graphic accelerators. A street grid layout for the viewing area is gen- erated based on local information and a small set of parameters. As users travel through the world the street grid is incrementally extended as needed. From the street grid, road geome- try and lot shapes can be generated. The lot shapes can be used in a subsequent step to gener- ate the content of the lot such as buildings. This approach facilitates the generation of extremely large cities consisting of lot shapes varying in size and shape. Keywords: procedural generation, virtual real- ity, games, architecture, real-time, deformable models * School of Creative Media RMIT University stefan.greuter@rmit.edu.au † School of Aerospace, Mechanical and Manufacturing Engineering RMIT University nigels@nigels.com ‡ School of Computer Science and Information Technology RMIT University gl@cs.rmit.edu.au 1 Introduction Many popular games are set in city or urban en- vironments. New generations of computer hard- ware allow developers to create increasingly large and detailed game worlds but the size and detail of game worlds is limited by time and production resources as well as technical and performance limitations. To create large game worlds artwork such as models and textures are often used repetitively. Clever placement of ob- stacles such as fences, mountains and rocks pre- vent the player from leaving the confines of the level. However, players become aware of the confines of the game world and notice repeti- tious use of models and textures. We believe that it is possible to use a procedu- ral texturing and modeling approach to generate extremely large game worlds without the need to reuse artwork repetitively. In our virtual cities project [1] procedural generation techniques are used to generate a ‘pseudo infinite’ city consist- ing of buildings each with individual geometry. Initially a regular square street grid was used. Here we detail a procedural pseudo-random ap- proach to improve the variation and reduce the repetition of a regular street grid. This paper is divided into six sections. Sec- tion 2 overviews related work. Section 3 de- scribes our real-time road network generation approach. Experimental results are presented Section 4. Section 5 discusses broader applica- tions of procedural generation techniques. Sec- tion 6 concludes the paper with final remarks.