This page provides information on the Volumetrics overrides rollout in the render settings.
The Volumetrics section allows you to use an environment volume in your scene, or enable probabilistic sampling for volumetrics.
||Render Settings window|| > Overrides tab > Volumetrics rollout
Use environment volume – When enabled, V-Ray overrides the default Maya environment and renders with the Environment volume loaded below.
Probabilistic volumetrics – If enabled, the volumetrics will select a few samples along each ray based on the smoke density, and evaluate the volume lighting at those points. If disabled, the volumetrics will evaluate the lighting at each step of the raymarching algorithm. The probabilistic mode is particularly useful when using the progressive sampler in V-Ray, as well as when using complex lighting on the volume. This mode only applies to the Volumetric Grid (VRayVolumeGrid) currently.
Num. prob. samples – The number of probabilistic samples to use when Probabilistic volumetrics is enabled. For best rendering performance, use higher number of samples for transparent smoke, and lower number for dense smoke. With very high number of samples, the sampling will basically converge to a standard ray-marching.
Num. GI prob. samples – The number of probabilistic samples to use for GI rays. The number of samples depends on whether the volumetric has emissive component. Brighter emission requires more samples, while pure smoke can work with fewer.