By Winfried Kurth
Among the techniques for the creation of photorealistic virtual organisms, particularly plants, and in scientific models of vegetation structure, rule-based specifications (formal grammars) play a prominent role. Lindenmayer systems (L-systems) are the most widespread formalism of this sort, but certain types of graph grammars, combined with standard object-oriented programming, offer even more possibilities to specify rule-driven developments of 3-dimensional arrangements, morphology of virtual organisms and underlying processes like, e.g., metabolic reactions. Examples of grammar rules and the virtual geometrical structures generated from them, all realizable with the open-source software GroIMP (www.grogra.de), are shown. This grammar-based approach is often not immediately used for the direct specification of a picture as a pattern of graphical elements in a plane, but for virtual 3-D scenes, which are then rendered visible using standard techniques of geometry-based computer graphics.