Mask of contact shadow using VRay Dirt ?

[doark]

http://youtu.be/xYYrlxwB7Eg?t=26m16s

Can anyone tell me, how he managed to calculate the shadow only of the ground? I can only calculate the AO for the entire scene! This type of mask is made by ID? I do not have an idea.

Thanks for the help!

[Morbid Angel]

He uses max, in there vray dirt has an exclusion list (where the dirt gets put on and where not). In maya there is a similar list called set include/exclude how it works is you create a simple maya selection set with objects you want to exclude from ao, so lets say in his case its everything but the ground where the car is. Then you connect the set to the vray dirt in section "useBy" and check it on.

And here is another thread about this too:

http://forums.chaosgroup.com/showthr...from-occlusion