Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
It's complicated. The -ab parameter sets a hard limit on the number of indirect diffuse bounces, so you should set this to some large number if you are concerned. That said, rcontrib (and rfluxmtx) do use Russian-roulette sampling by default (-lr -10 from "rcontrib -defaults"), and follow a path-tracing protocol when it comes to the indirect diffuse component. If you set -ab 10, then Russian-roulette will decide ray termination in most cases in an unbiased fashion. The -lw setting together with -ad will decide how many ray paths are followed, and lw*ld should be > 1.
Since rcontrib and Russian-roulette sampling are more recent additions, Rendering with Radiance does not cover them.
I hope this helps
| | 2 | No.2 Revision |
It's complicated. The -ab parameter sets a hard limit on the number of indirect diffuse bounces, so you should set this to some large number if you are concerned. That said, rcontrib (and rfluxmtx) do use Russian-roulette sampling by default (-lr -10 from "rcontrib -defaults"), and follow a path-tracing protocol when it comes to the indirect diffuse component. If you set -ab 10, then Russian-roulette will decide ray termination in most cases in an unbiased fashion. The -lw setting together with -ad will decide how many ray paths are followed, and lw*ld should be > 1.
Since rcontrib and Russian-roulette sampling are more recent additions, Rendering with Radiance does not cover them.
Regarding the -av setting, this is used as a "remainder" in the infinite series once the finite number of terms corresponding to your -ab setting has been computed. It should roughly equal the average radiance in your scene in any direction, but can be safely set to "0 0 0" for unknown conditions.
I hope this helps
