Reducing Ray - Object Intersections
First - hit Speedup
As mentioned in the section on adaptive depth control, by using that technique the average depth of the ray tree may be less than two. This means that a large percentage of the work is performed in finding the first intersection.
Weghorst has suggested using a modified Z-buffer algorithm to determine the first hit. The scene would be pre-processed, with the resultant z-buffer storing pointers to the objects intersected. Then the ray tracing would proceed from that point.
He showed that incorporating the above three techniques (adaptive depth control, hierarchical bounding volumes, and first-hit speedup) approximately halved the intersection computational time for complex scenes. Note that he use spheres as the bounding volumes. In general the computational improvement was inversely dependent on scene complexity.