Out-of-core encoding of large tetrahedral meshes

• Authors: Shyh-Kuang Ueng
• Venue: VG '03 Proceedings of the 2003 Eurographics/IEEE TVCG Workshop on Volume graphics
• Year: 2003

In this paper, an out-of-core data compression method is presented to encode large Finite Element Analysis (FEA) meshes. The method is comprised with two stages. At the first stage, the input FEA mesh is divided into blocks, called octants, based on an octree structure. Each octant must contain less FEA cells than a predefined limit such that it can fit into the main memory. Octants produced in the data division are stored in disk files. At the second stage, the octree is traversed to enumerate all the octants. These octants are fetched into the main memory and compressed there one by one. To compress an octant, the cell connectivities of the octant are computed. The connectivities are represented by using an adjacency graph. In the graph, a graph vertex represents an FEA cell, and if two cells are adjacent by sharing a face then an edge is drawn between the corresponding vertices of the cells. Next the adjacency graph is traversed by using a depth first search, and the mesh is split into tetrahedral strips. In a tetrahedral strip, every two consecutive cells share a face, and only one vertex reference is needed for specifying a cell. Therefore, less memory space is required for storing the mesh. According to the different situations encountered during the depth first search, the tetrahedral strips are encoded by using four types of instructions. When the traversal is completed, the tetrahedral strips are converted into a byte string and written into a disk file. To decode the compressed mesh, the instructions kept in the disk file are fetched into the main memory in blocks. For each block of instructions, the instructions are executed one by one to reconstruct the mesh. Test results reveal that the out-of-core compression method can compress large meshes on a desk-top machine with moderate memory space within reasonable time. The out-of-core method also achieves better compression ratios than an incore method which was developed in a previous research.