The Ray Tree

When ray tracing a scene, reflected or transmitted rays may strike other reflective or transparent objects. Further reflected or transmitted rays will be spawned, and so on. Taken together, such a family of rays is termed the ray tree. Care must be taken to control the depth of this tree: If it is allowed to grow too deeply, one may spend a great deal of time computing rays that contribute little to the final picture; if it is not allowed to grow far enough, this premature tree pruning may be evident in the image.

provides two complementary methods for controlling the depth of the ray tree. One method sets an absolute maximum for the tree. The other allows one to adaptively prune a tree as it grows so that ``unimportant'' rays are not spawned.

$\begin{defkey}{maxdepth}{{\em level}} Do not spawn rays deeper than those at the given {\em level}. \end{defkey}$
Rays from the eye are of depth zero. The default value for level is 15. This depth may also be set from the command line through the -D option.

$\begin{defkey}{cutoff}{{\em threshold}} Do not spawn rays whose contribution to... ...n as a single floating-point value, or as a red-green-blue triple. \end{defkey}$
The default value is 0.002. This threshold may also be set from the command line through the -T option.