Compositor and certified Nike Trainer, Erwan Leroy thinks some things in Vray are easy. Yet, some other things, might be a bit convoluted, and needs more of your attention. You can find plenty of tutorials that cover creating custom render passes in VRay. There aren’t a lot of tutorials that cover creating a (Pref) position reference pass.
As a compositor, Erwan used position reference passes all the time. The only mystery seemed the “how” with Vray.
Position Reference Passes
A popular render pass is the Pworld pass. It can also known as Position World Pass, XYZ, or Point Position. What ever it’s name, a Pworld can be for relighting or pt make position based mattes. The Pref, or Position Reference can look a lot like the Pworld, but the colors “stick” to moving objects.
Check out Erwan Leroy’s article that shows how you can Create Position Reference (Pref) Pass in Vray for Maya.