Geometry Coding and VRML

The Virtual Reality Modeling Language (VRML) is rapidly becoming the standard file format for transmitting 3D virtual worlds across the Internet. Static and dynamic descriptions of 3D objects, multimedia content, and a variety of hyperlinks can be represented in VRML files. Both VRML browsers and authoring tools for the creation of VRML files are widely available for several different platforms. In this paper we describe the topologically-assisted geometric compression technology included in our proposal for the VRML Compressed Binary Format. This technology produces significant reduction of file sizes and, subsequently, of the time required for transmission of such files across the Internet. Compression ratios of up to 50:1 or more are achieved for large models. The proposal also includes combines a binary encoding to create compact, rapidly-parsable binary VRML files. The proposal is currently being evaluated by the Compressed Binary Format Working Group of the VRML Consortium as a possible extension of the VRML Standard. In the topologically-assisted compression compression scheme a polyhedron is representedusing two interlocking trees: a spanning tree of vertices and a spanning tree of triangles. The connectivity information represented in other compact schemes, such as triangular strips and generalized triangular meshes, can be directly derived from this representation. Connectivity information for large models is compressed with storage requirements approaching one bit per triangle. A variable length, optionally lossy compression technique is used for vertex positions, normals, colors, and texture coordinates. The format supports all VRML property binding conventions. CR