I was looking at some of the assets for the Matrix demo and they have an interesting Dirt Map on their assets. It is part of the Red channel in the texture. It looks like a procedural map since all the assets have something similar.

I have tried 'Grouping' the primitives, 'Keep By Normals' with a -1 in the Y Direction, Spread Angle of 45. Add a Color, Blur the Cd Attribute. In the end it doesn't seem right. This post helped a bit with using Edge Angle. Select primitives or edges by angle [www.sidefx.com]

I tried an approach of using particle emission based on an Occlusion Map as a Wet map. Not the best results.

Instead of recreating this type of texture map using VEX/Cops, I ended creating a texture baker setup using Python, Labs Quick Material, and Labs Maps Baker. That takes the original maps and transfers them to new UVs.

Glen