When It Makes Sense to Use Uniform Grids for Ray Tracing

Commonly used hierarchical data structures such as bounding volume hierarchies and kd-trees have rather high build times, which can be a bottleneck for applications rebuilding or updating the acceleration structure required by data changes. On the other hand uniform grids can be built almost instantly in linear time, however, they can suffer from severe performance penalty, in particular in scenes with non-uniformly populated geometry. We improve on performance using a two-step approach that combines both approaches: first we build a uniform grid and test its performance. Second, using an estimate on the number of rays to be queried we either continue using the grid or build a hierarchical data structure instead. This way we select a more efficient data structure given a particular implementation of the algorithms which yields with high probability an overall smaller computational time. We evaluate the properties of this method for a set of 28 scenes