Streaming meshes

Recent years have seen an immense increase in the complexity of geometric data sets. Today\´s gigabyte-sized polygon models can no longer be completely loaded into the main memory of common desktop PCs. Unfortunately, current mesh formats, which were designed years ago when meshes were orders of magnitudes smaller, do not account for this. Using such formats to store large meshes is inefficient and complicates all subsequent processing. We describe a streaming format for polygon meshes that is simple enough to replace current offline mesh formats and is more suitable for representing large data sets. Furthermore, it is an ideal input and output format for I/O-efficient out-of-core algorithms that process meshes in a streaming, possibly pipelined, fashion. This paper chiefly concerns the underlying theory and the practical aspects of creating and working with this new representation. In particular, we describe desirable qualities for streaming meshes and methods for converting meshes from a traditional to a streaming format. A central theme of this paper is the issue of coherent and compatible layouts of the mesh vertices and polygons. We present metrics and diagrams that characterize the coherence of a mesh layout and suggest appropriate strategies for improving its "streamability". To this end, we outline several out-of-core algorithms for reordering meshes with poor coherence, and present results for a menagerie of well known and generally incoherent surface meshes.