Point Base and Brickmaps in RMSGIPtcLight

In the Renderman Studio there is an option to cache GI into Point Clouds or Brickmaps, using RMSGIPtcLight node.

There are three options for Bake Type.

Information about the Point Clouds and Brickmaps usage are the best of my knowledge at the moment.

1)  rmanRenderRadiosityPass
- this first method will simply generate a point cloud file (rmanRenderRadiosityPass.0001.ptc). This point cloud will store the direct illumination data and the actual indirect calculation(The last bounce) will still need to be calculated during the beauty render. Having a point cloud file allows Renderman to load the point cloud scene into memory and use it for indirect illumination calculation.

2) rmanPartialFilterApproxGlobalDiffusePass
- this second method will first output a rmanRenderRadiosityPass.ptc point cloud file, the same as the first method, then run a PTFilter command on this point cloud to generate the next point cloud, rmanPartialFilterApproxGlobalDiffusePass.ptc which store indirect illumination data in it. The name Partial might suggest that the last ray bounce will still need to be calculated at beauty rendering time. The benefit of this second rmanPartialFilterApproxGlobalDiffusePass is that it enable more than one bounce to be performed.

3) rmanMakeFilterApproxGlobalDiffusePass
- the third method will generate two point cloud files and a brick map file. As usual rmanRenderRadiosityPass.0001.ptc will be first generated. PTFilter command will run and process this point cloud file to generate the second point cloud file rmanFilterApproxGlobalDiffusePass.0001.ptc. This second point cloud file has more data, includes indirect diffuse, occlusion. Later, the next command brickmake will be run on the second point cloud file to generate a brickmap file.

So the question will be which method will be the best option for certain scenario. In a very early conclusion, brickmap method seems to be the best as it is more memory efficient as brickmap data has multi resolution level which can be loaded accordingly. For example the buildings far away in the background will use the first level, the most "light" version. However, there will be pre point cloud pass needed for brickmap generations. 

Point cloud file on the other hand is an unorganized data. A more efficient way to create Point Cloud file will be the use of Organize Point Cloud format, which storing its data in Octree. But then again, a pre pass point cloud file will be needed.

Full ray trace will be the more elegant solution then :)