Experiences with Streaming Construction of SAH KD-Trees

A major reason for the recent advancements in ray tracing performance is the use of optimized acceleration structures, namely kd-trees based on the surface area heuristic (SAH). Though algorithms exist to build these search trees in O(n log n), the construction times for larger scenes are still high and do not allow for rebuilding the kd-tree every frame to support dynamic changes. In this paper we propose modifications to previous kd-tree construction algorithms that significantly increase the coherence of memory accesses during construction of the kd-tree. Additionally we provide theoretical and practical results regarding conservatively sub-sampling of the SAH cost function