RapidRay is a raytracing acceleration system built specifically for Sitni Sati's 3ds Max plug-in DreamScape. (DreamScape enables you to create dynamic natural scenery in 3ds max, such as realistic skies, clouds, terrains and ocean surfaces.)
RapidRay is also used in AfterBurn 4.0 to accelerate intersections with objects during HyperSolids reflection/refraction effects.
Max. Depth - This parameter represents the maximum depth of grid nesting. Higher values might result in shorter rendering times, but nested grids will occupy much more RAM.
Max. Faces/Voxel - Each cell of a uniform grid is called a "voxel." When a voxel contains more faces than specified by this parameter, this cell will be subdivided until the Maximum faces per voxel or Maximum depth limit is reached.
Max. Width - Each grid is subdivided into a number of smaller voxels, where this parameter limits the number of grid dividing voxels.
Raytracing Max. - The maximum number of bounces the ray can do.