Geometry coding and VRML

Abstract

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 represented using 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.

Compressing the property mapping of polygon meshes

“…Our predictive compression scheme results in bit-rates between 0.1 and 2 bpv, which improves by a factor of 2 to 10 over previous methods [18,5,8].…”

Encoding normal vectors using optimized spherical coordinates

“…We demonstrate the performance of our method by comparing it to several other methods including Healpix [3], octahedral subdivision (Octa) [6,7,8,9], octahedral normal vectors (ONV) [4], sextant encoding (Sextant) [5], and the sphere1 covering (Sphere1) [9]. As test data, we use normal vectors generated from the polygons of common surfaces found in Computer Graphics.…”

“…The most well-known and popular method for encoding unit vectors is based on octahedron subdivision [6,7,8,9]. The method begins with an octahedron and alternates linear subdivision and projection back to the sphere to build a point distribution.…”

Recent Advances in Compression of 3D Meshes

“…The early works usually quantize uniformly the vertex positions for each coordinate separately in Cartesian space [Dee95,THRL98,TG98], and a more sophisticated vector quantization has also been proposed by Lee and Ko [LK00]. Karni and Gotsman [KG00] have also demonstrated the relevance of applying quantization in the space of spectral coefficients (see [GGK02] for more details on this approach).…”

“…The early work employed simple delta coding [Dee95] or linear prediction along a vertex ordering dictated by the coding of the connectivity [THRL98,TG98]. The approach proposed by Lee et al [LAD02] consists of quantizing in the angle space after prediction.…”