Geometric substitution: a tutorial

A collection of rewrite rules that transform simple polyhedral models (and polyhedral control meshes) into richer, more visually expressive models is presented. All are based on simple transformations that can be easily implemented and extended. The focus is mostly on techniques of cell replacement, where a unit of the structure (typically a polygon or polyhedron) is replaced by one or more variant units. Such replacements are encoded in rewrite rules. The approach presented helps a modeler who, having created a simple low-detail model, wants to amplify that shape´s complexity. Features of the substrate model (such as symmetry relationships and prominent surface features) are generally conserved and often echoed and enhanced in the amplified shape.<>