The Render Manager > mental ray (Global Renderer)
The Render Manager > (expand a pass) > mental ray
Set the current pass and choose Render > Render > Renderer Options from the Render toolbar.
Tab: Accuracy [Properties Reference]
Options: Map File and GI and Caustics.
The final gathering map is a file that stores the final gathering information calculated before and sometimes during rendering. The final gather points recorded in earlier frames are reused in subsequent frames, saving a great deal of computation time.
The final gathering map records the final gathering accuracy value when the map is first generated. If the accuracy value changes, such as between two renders of the same scene, the map is ignored, the final gather points regenerated, and a new final gathering map is created.
To generate a final gathering map
Specify a name and path for the final gathering map in the Map File text box. The current path is displayed in the Resolved Map File Path text box.
Select one of the Map File Settings to define how the final gathering map file is used. Choose one of the following modes:
Overwrite file with generated FG points computes final gathering points at each frame and stores the results in a final gathering map file that overwrites any existing map file. In other words, the final gathering map is rebuilt at each frame.
This is a good setting for scenes where lights or objects change frequently, or where the camera moves to a point where objects that were visible in earlier frames are no longer visible.
Append generated FG points to file uses an existing final gathering map file or calculates one for the first rendered frame. If mental ray computes additional final gathering points for subsequent frames at render time, these points are appended to the map file.
This is especially useful in the case of small camera movements because final gathering results depend on the camera's position.
Generate FG points only if file doesn't exist uses an existing final gathering map (or calculates one for the first rendered frame), but does not append any new points computed at render time. After the initial computation, the map file is only modified if you change the final gathering Number of Rays value. This is useful for render farm setups where several machines may use the same final gathering map.
Final gathering calculations are based on the position of the pass camera. If you are using this setting, make sure that the map file contains sufficient final gathering data for all camera positions in the rendered sequence.
Creating Per-Object Final Gathering Maps
Each object in a scene can have its own final gathering map. When you create a final gathering map for a single object, the object's sampling points are no longer included in the scene-wide map.
At render time, per-object maps are computed along with the scene-wide map, according to the Map File Setting specified in the Render Manager.
