Grid creation paper

Here is a pdf file of a new paper by Thiago Ize, Steve Parker, and myself. It will appear in Ulm at RT07 It does some theory on how to build grids within grids. It is a follow-on to the classic Jevans and Wyvill paper. Its main practical result is that for a two level grid of small triangles, use N**(1/5) subdivisions in each dimension, and then in occupied cells use M**(1/3) where M is the number of primitives in that cell. For single ray code this seems to work quite well. There is also some analysis for long-skinny triangles (like you might get subdividing a cylinder) which says grids are bad at such scenes. That being said, BVH with AABB and k-d are probably even worse!