Volumetric

Heat Haze – Traces the ray changing direction according to the gradient of the Surface channel. A value of 1 corresponds approximately to the normal heat haze in the air caused by the temperature. If smoke or another channel is selected as the source, a larger value might be necessary to achieve a visible result. You can manually input values higher than 1. A value of 0 produces no heat haze. This parameter is available only when the Mode is set to Volumetric Heat Haze. See the Heat Haze example.

Volumetric Material ID –  Material ID color for the MateralID Render Element when rendering in any of the Volumetric Render Modes. When rendering in Isosurface or Mesh Render Mode, this will be taken from the assigned material.

Volumetric ZDepth – Used to generate a z-depth render element in Volumetric Render Mode.

Disable – Disables generating the render element.
Standard Element - The z-depth of the volume will be written to the V-Ray ZDepth render element.
Separate Element - The z-depth of the volume will be written to a new zDepth render element.

Volumetric Normals – Used to generate a render element with volumetric normals in Volumetric Render Mode. Since V-Ray does not allow volumetrics to write into the normals RE, the result is written to a separate RE.

Disable – Disables generating the render element.
Separate Element – The volumetric normals of the volume are written to a new Normals render element.