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International Journal of Computer Games Technology
Volume 2015 (2015), Article ID 808904, 15 pages
Research Article

Procedural Content Graphs for Urban Modeling

1Faculdade de Engenharia/INESC TEC, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
2Computer Graphics and Visualization Group, Delft University of Technology, Mekelweg 4, 2628 CD Delft, Netherlands

Received 22 April 2015; Accepted 28 May 2015

Academic Editor: Hanqiu Sun

Copyright © 2015 Pedro Brandão Silva et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Massive procedural content creation, for example, for virtual urban environments, is a difficult, yet important challenge. While shape grammars are a popular example of effectiveness in architectural modeling, they have clear limitations regarding readability, manageability, and expressive power when addressing a variety of complex structural designs. Moreover, shape grammars aim at geometry specification and do not facilitate integration with other types of content, such as textures or light sources, which could rather accompany the generation process. We present procedural content graphs, a graph-based solution for procedural generation that addresses all these issues in a visual, flexible, and more expressive manner. Besides integrating handling of diverse types of content, this approach introduces collective entity manipulation as lists, seamlessly providing features such as advanced filtering, grouping, merging, ordering, and aggregation, essentially unavailable in shape grammars. Hereby, separated entities can be easily merged or just analyzed together in order to perform a variety of context-based decisions and operations. The advantages of this approach are illustrated via examples of tasks that are either very cumbersome or simply impossible to express with previous grammar approaches.