Hello guys, I’m a concept artist learning about the matte painting world. Recently I started this project so I draw my sketch, builded the 3D geometry, texturized and lighted in Maya using Mentalray, now I want to render the image, and i want to know how to generate the “depth alpha” or a way to select using a mask (black and white) with information about how far are the elements from the camera. The same way I would like to see the occlusion mask, lighting and shadow to adjust it in photoshop.
For this image I’m following the tutorial from Raphael Lacoste (Gnomon) but he skips on the technical side of this step (he uses 3dmax and the tutorial is focused in the Photoshop side of the work).
Any help, tip of direction will be of great help, thanks a lot 
Rizo