Being in an internet era, the rapid transmission of 3D mesh models is getting more Important and efforts toward the compression of various aspects of mesh models have been provided Even though a mesh model usually consists of coor-dinates of vertices and

Being in an internet era, the rapid transmission of 3D mesh models is getting more important and efforts toward the compression of various aspects of mesh models have been provided. Even though a mesh model usually consists of coordinates of vertices and properties such as colors and normals, topology plays the most important part in the compression of other information in the models. Despite the extensive studies on Edgebreaker, the most frequently used and rigorously evaluated topology compressor, the probability distribution of its five op-codes, C, R, E, S, and L, has never been rigorously analyzed yet. In this paper, we present probability distribution of the op-codes which is useful for both the optimization of the compression performance and a priori estimation of compressed file size.

STEP is the international standard for the computer-interpretable representation and exchange of product data. STEP physical file as the implementation method of STEP generally has a large file size which may be an obstacle of efficient use and seamless transition through network. Therefore, the compression of STEP physical file has been interested recently. In this paper, we present the compression algorithm of STEP physical file. STEP physical file is compressed by LZ77 with an appropriate search buffer size for STEP physical file and Huffman coding is applied to the result of LZ77. The proposed algorithm obtains the significant compression ratio.

Since transmitting various files around Internet is one of common activities in everyday life, the compression is important technical issue in these days. Shape models are also frequently transmitted and therefore its compression has also been studied. Considering the large portion of shape model can be normal vectors, a new scheme was recently presented to compress normal vectors using clustering and mixed indexing scheme. Presented in this paper is a mathematical investigation of the scheme to analyze the probability distribution of normal index distances in Normal Index array which is critical for the compression. The probability distribution is formulated so that the values can be easily calculated once the relative probabilities of C, R, E, S, and L op-codes in Edgebreaker are known. It can be shown that the distribution of index distances can be easily transformed into a few measures for the compression performance of the proposed algorithm.