This is a new one that cropped up today and is killing me.

I need to render ambient occlusion using render to texture. No problem so far. Ive done this a lot before so I know the steps.

Weirdly, my results today show black wherever the low res model intersects the high (?????!!!!) This would mean that mental ray is now including the low res mesh in its calculations. AAHHHHHHHGGGGGG!!!!!
Is this just me or is this now a critical bug?

I only know how to cast a GI map.. no idea how to do AO.. post yer process and Ill give it a run, and see if I get the same problem..

as it stands you cant use MR to render AO on a projected model, you have to use skylight + advanced lighting and output a lighting pass using max's scanline renderer instead of MR

Yeah...IM with these guys. I've never been able to do an AO bake in max using a projected model.

Just use skylight with lightracer

Render to texture works fine in Mental Ray. when you have it set as your default renderer, an ambient occlusion map(MR) is added to the types of maps you can render out as.

I'm pretty sure you must have tried resetting xforms/checking your normals, right?

Dave I got this same error before. Never got passed it. Drove me INSANE!!!

I have to say I generate my AO maps using a skylight and light tracer as well.

I seem to vaguely remember having the same problem with rendering AO maps with mental ray myself as well.

hmm I read of a workaround for this. something about changing material id stuff the in the mental ray shader. its on the UDN if you are an unreal engine 3 licencee

Yeah theres a workaround someone posted on UDN - baking the Mental Ray material into the diffuse slot or something...can't remember the exact steps but the results were almost identical to adding a skylight and lighttracer to your scene...only more unwieldy to set up!

You can exclude object-ID's with the AO-Shader, the Render To Texture dialog misses that option unfortunately. By putting an AO in the diffuse-slot of your source geometry and setting SelfIllumination to 100% you can bake an AO-pass and still be able to exclude single objects. That means of course that you can't bake diffuse and AO at the same time. Would be great if there's a better workaround like excluding objects from being visible to AO in general.

Same bug is in Max9, drove me crazy for hours.

OLD THREAD ALERT!
Question: Why is everyone using mental ray to bake AO when the skylight + advanced lighting solution works fine? You can set up all sorts of nice bounce lighting and tweak the settings in there for a nice fast and high quality bake, and it doesn't take ages to set up - just add a skylight, set its colour to white, turn on Adv. Lighting, set the rays down from 250 to 50 or something and bake it... I haven't had any problems with that.

Is there something mental ray does noticeably better or faster?

All I have to do is set the renderer to mental ray, and select the AO map to be rendered in the render to texture dialog.

to tell you guys the truth, i actually get much better results using an oldschool light dome setup.. there are several scripts for this.. choose the one you like the best, but for some reason i find the light dome results seem to catch the details better than the skylight.

yeah i got this and gave up on it really quickly. TBH amb occ maps suck anyway. trying to overlay one on you diffuse map is akin to painting charcoal edges on your colour work

Yeah, I totally agree. But the minute spent on the ao map helps me out greatly when I'm painting the texture in bodypaint in a fullbright environment.

I found that putting a negative push on the lo model before baking fixed it so it was beneath the hipoly, since the object id exclusion seems a bit dodgy

Or you could perhaps make the lowpoly invisible or non renderable?

Yeah, you could right-click on the low-poly, go to properties and turn off the cast shadows option? Works for me.

->Toomas-Jaco - you right
1-When bake Ambient Occlusion with mental Ray Occlusion shader for light(NOT Global Illum. like lightracer do, ITS DIFFERENT Things) in objects properties of your low-poly UNCHECK in Render control all radio buttons exclude Renderable(if ucheck- bake to texture will fall everytime)
Your low-poly will renderable but not visible in render frame window(is it bug of MR working with BakeToTexture?)
2- Ambient occlusion is procedurical shadow, its show places where light is attentuate(fall off?? Sorry my english Im from russia))) and its work something like dyrt, its not lighten deep places even light point directly cast light to it, GI instead can lighten deep places of your object.
AO generated by every part of your model? in max you can setup spread angle, the more rays casted from every point of your model hit surface- the more darkly this part of surface. Flat surface with spread <0.9 will bright, more 0.9 it will self shadowing(dont use more than 0.8
Thats why Ambient Ocllussion more preferable then GI type of light.

I forgot about this thread!

Ok, the way to do this is to use the G-Buffer.

Set your low poly objects G-buffer to, say, 15.
Then in your Ambient occlusion map set the include/excl. Object ID to negative 15 (-15).
This will then exclude the low poly from the shadow solution.

The previous suggestions about turning off object property renderable etc does not work.

Hope that helps anyone out there from pulling out their hair.

So do you use an actual mental ray shader with ambient occlusion in the surface slot to render your ambient occlusion map? I've never needed to use a material to render an ambient occlusion map using render to texture. Do you apply the material to the lowpoly or the highpoly? I've tried to render an ambient occlusion map this way but it just comes out blank.

i know this is really old, but i had the same problem and finaly got the answer to the problem...

the key is that the cage can not be reset. it needs a value over 0. OR you could use
an offset in the optons setup of the "render to texture" dialog.

here is a nice tutorial: http://www.ai-dallas.com/student/Hay...ion%20Maps.pdf
mabye this still is interesting for some people..
cheers