Mental Ray issues.

[shinobix]

Hey Guys,
The other night I was trying to render out some Ambient Occlusion maps in Max using mental ray.
Usually when I do render to texture AO maps, I just throw a skylight into the scene and use lighttracer to get my map.
But I would like to experiment with mental ray maps. Problem is, is that when I do the RTT, it looks correct in the render viewport, but the exported map is actually pure black.
I've looked into this and keep getting the same results. I'm obviously missing a step or two ;)
Can anyone help me out please?? I've been trying to find good tutorials on this, but have come up somewhat empty in my searches.

Cheers!

[Mark Dygert]

First off ignore whatever it puts in the render preview window, this can not be trusted, ever. It is a full render of the object and normally contains scene lighting which in most cases is the viewport lighting. If you move your view around to another spot on the model it will render differently, don't trust it, just ignore it, even if it "appears to look right".

2nd there is a lot that can go wrong. And a lot depends on the object.
Are you baking AO from a high poly to a low?
If so are you using a projection cage or ray depth?
Have you unwrapped the model? In RTT is it set to "Use Existing Channel" and the channel is set to the correct channel?

Try these settings: http://dl.dropbox.com/u/2336353/RTT.jpg
These are probably helpful:
http://www.laurenscorijn.com/articles/ambient-occlusion-baking
http://wiki.polycount.com/AmbientOcclusionMap?highlight=%28\bCategoryTexturi ng\b%29#A3ds_Max_Baking_Methods

[shinobix]

Hey Vig,
Currently its just a low poly geo (an environment assets). I've got the uv's set in channel 1 for the dif, spec, norm, and would like the 2nd uv set for the AO. The engine we're using here doesn't bake in lightmaps and stuff 'in engine' like unreal, so I have to do it all in Max. Wee.
I'll take a look at those links and see if they help out. I'll let you know what happens :D

Thank you!

[shinobix]

Oh my god...
Vig, I am grateful for your help! Turns out I was having an ID10T error ;)
I had the mental ray shader with the Ambient/Reflective Occlusion material applied to my object, which renders out black. As soon as I put a default shader on it, it worked :D
Thanks again for your help, and I've bookmarked those links you posted. There's some awesome info / tips in there :D