Is this possible ?
I realise that variations in thickness of the surface creates differences in fog multiplier, but is it possible to control the fog via a texturemap.
I was hoping to apply a gradient map so that the fog is high at the lower point on the mesh and only small amounts at the top…without having to alter the mesh itself.
Cheers
Been on the wishlist a couple of times already. So to say, a must have feature. Vlado said that 3d shaders would be necessary to map the fog, and it’s tricky to transform 2d maps to map the fog color. I however disagree on that, but hey, I’m not the one writing Vay. 
If you need a simple gradient, or the blend of just few colors, try using a VRayBlend shader and map the blend amount. Results will be exactly like mapping with 2D, bit cumbersome though.
Best regards,
A.
someone here on the forum mentioned to put the vray sky in the fog colormap, seems to work pretty well.