Location:
The Render Manager > mental ray (Global Renderer)
The Render Manager > (select a pass) > mental ray
Set a current pass and choose Render > Render > Renderer Options from the Render toolbar.
Tab: Irradiance Particles
Options: Rebuild Map and Photon Global [Properties Reference]
Sometimes you do not want to rebuild the entire particle map at every frame. Instead, you want to write the particle map to disk once and reuse it. For this case, you can use the irradiance particles map which works in the same way as do photon or final gather maps.
If the file specified in Particle Map File textbox exists on disk and Rebuild is off, then mental ray reads the map file instead of computing a new particle map.
If mental ray cannot find the map file, it computes the map and saves it under the given name.
If you turn Rebuild on, mental ray always computes the particle map.
