Observer Rules for Box-Split Grammars

Grammars are well-suited for the generation of structured content, such as text. Some specialized grammars, such as Shape Grammars, can even be used to generate 3D structures inside a game world like Minecraft. However, the top-down nature of grammars present limitations when it comes to modeling structures that should be connected to or utilize given geometry. In this paper, we describe an extension to an existing grammar model, called Box-Split Grammars, that extends it with the ability to observe existing geometry during the generation process, in order to incorporate it propertly into the generated structures. This modification also requires the addition of back-tracking in order to handle states in which certain geometry was (not) observed. We demonstrate the utility of this extension by showing how it can be used to place support structures for bridges and tunnels in a way that fits within an existing landscape