High to Low Ambient Occlusion

Uly

Lately I've taken a few swings at projecting an AO Map/Dirtmap from a high poly prop for the low poly prop's texture. Stupid things happen, mainly raycasting issues.



Here's a pic of the resulting AO map generated by Max using Mental ray.

I'm projecting this using a cage, and the cage envelops the model as it should. Already generated a working normal map with the same cage, & without any raycast errors. (Also, this is what a certain component of the prop generated. Black space is from other components that weren't included in the projection.) Any tips are appreciated, thanks mans.

Castor

If you are having so much trouble rendering the ambient occlusion map off the high polygon model, try just rendering it out off your normal map. It is not as accurate and complete, maybe you can use the combination to archive the best result possible.

indian_boy

i believe xNormal can render AO maps? its a bit slow to render, but its results are good from what i've seen.

Joao Sapiro

yeah use Xnormal, i also had shitload of artifacts in max, and in xnormal besides beeing faster you can adjust easily the raycast distance and that my friend is a life saver !

Kevin Albers

Mental ray seems a bit error-prone in Max using render-to-texture. I've given up using the mental ray AO for now, and instead render out a lighting map using the scanline renderer, with a single white skylight in the scene. I'd like to use the mental ray AO more often...hopefully these issues will be resolved in the next version of Max.

vahl

use faogen

FatAssasin

Are there overlapping (coincident) faces between the high res and low res models in those areas? That will cause problems. If so, just apply a Push modifier on the high res mesh with a really small value to move the face apart a bit.

MoP

Also you could try turning off shadow casting on any meshes not directly meant to be casting AO (ie. any lowpoly meshes you're baking to - right click on them and look in properties, turn off shadow casting).

FatAssasin

Oh, and I just remembered, until Max 9.5, the low res mesh will be included in your ambient occlusion pass (it's a bug). There's a workaround which I'm sure someone has posted here before. That's most likely where your problem is.

j_bradford

Damn I love mental ray AO for RTT. You may want to try turning off the cage in the projection mapping dialog box. I do that but still adjust a cage depth anyway. It tends to get rid of a lot of the red artifact errors for me.

Uly

Thanks a lot for the tips guys. I'm gonna go through a few of the methods and post my results. Epic win.

Ghostscape

Mental Ray tends to screw things up with AO maps so I just bake using a skylight and the scanline renderer. I know I should be using xNormal because everyone loves it, but switching out to a separate program like that just slows down my workflow.

StJoris

I'm no Guru but perhaps doing an AO RTT on the highpoly model with auto-uv's and using RTT to bake that to your lowpoly model?

Asmuel

Can faogen do highpoly to lowpoly AO without UV's on the Highpoly? Tried it but gave up a while ago (too lazy to persist with it )

vahl

yes, using vertex colors