ABSTRACT Early-Split Coding of Triangle Mesh Connectivity.pdfVIP

Early-Split Coding of Triangle Mesh Connectivity Martin Isenburg UC Berkeley isenburg@ Jack Snoeyink UNC Chapel Hill snoeyink@ ABSTRACT The two main schemes for coding triangle mesh connectivity tra- verse a mesh with similar region-growing operations. Rossignac’s Edgebreaker uses triangle labels to encode the traversal whereas the coder of Touma and Gotsman uses vertex degrees. Although both schemes are guided by the same spiraling spanning tree, they pro- cess triangles in a different order, making it difficult to understand their similarities and to explain their varying compression success. We describe a coding scheme that can operate like a label-based coder similar to Edgebreaker or like a degree-based coder similar to the TG coder. In either mode our coder processes vertices and triangles in the same order by performing the so-called “split op- erations” earlier than previous schemes. The main insights offered by this unified view are (a) that compression rates depend mainly on the choice of decoding strategy and less on whether labels or degrees are used and (b) how to do degree coding without storing “split” offsets. Furthermore we describe a new heuristic that allows the TG coder’s bit-rates to drop below the vertex degree entropy. CR Categories: I.3.5 [Computational Geometry and Object Mod- eling]: Boundary representations Keywords: Connectivity compression, label coding, degree cod- ing, split offsets, Edgebreaker, TG coder, Cut-border Machine. 1 INTRODUCTION A number of schemes for coding the connectivity of triangular meshes have been proposed [3, 11, 14]. All these schemes grow a region on the mesh by including triangle after triangle into a bound- ary and encode a sequence of symbols that documents this process. The Edgebreaker scheme [11] and the Cut-border Machine [3] are label-based approaches. They encode for each triangle how its in- clusion changes the boundary using one of five labels. The TG coder [14] is a degree-based approach. It only enco