Connectivity compression for irregular quadrilateral meshes

Applications that require Internet access to remote 3D datasets are often limited by the storage costs of 3D models. Several compression methods are available to address these limits for objects represented by triangle meshes. Many CAD and VRML models, however, are represented as quadrilateral meshes or mixed triangle/quadrilateral meshes, and these models may also require compression. We present an algorithm for compressing such quadrilateral meshes, and we demonstrate that in general they may be encoded with fewer bits than triangle meshes with the same number of vertices. By preserving and exploiting the original quad structure, our approach achieves encodings 30-80% smaller than an approach based on randomly splitting quads into triangles. We present both a code with a proven worst-case cost of 2.67 bits per vertex for meshes without valence-two vertices and entropy-coding results for typical meshes ranging from 0.3 to 0.9 bits per vertex, depending on the regularity of the mesh. Our method may be implemented by a rule for a particular splitting of quads into triangles and by using the compression and decompression algorithms introduced in [Rossignac99] and [Rossignac&Szymczak99]. We also present extensions to the algorithm to compress meshes with holes and handles and meshes containing triangles and other polygons as well as quads.