Problem with DR, Dirt AO and simple planes

[dlparisi]

I'm trying to render out a AO pass of an exterior I'm working and am having trouble with DR nodes rendering simple surfaces as flipped. In the two examples below- the one on the left is with DR (with 64 pixel grid overlay), the one on the right is no DR. As you can see parts of the railing are rendering flipped in all of the non-local DR buckets. The AO material is a standard material set to 2-sided with a dirt material in the self illumination slot and white in the diffuse.

The railing is modeled in autocad as regions and linked into Max 9 64bit. All nodes are 64bit as well with the same SP1 version of Vray. Other than the usual "don't model in AutoCAD", what's going on here? It renders just fine as long as I don't use DR. I also tried initiating the DR render from one of the render nodes and got similar results (the local node buckets were fine, the DR buckets were flipped) so it's not related to the machine I think. Granted, I can fix this whole thing pretty easily by just rendering locally or shelling the railing pieces by a small amount but I'd like to know if there's something I'm missing or have set up wrong.

Thanks.

[Neilg]

Why are you using a standard material, is having the 2 side distinction important?

Just use a vray material.

[instinct]

Did you try raising the Secondary Ray bias (to 0.002 or something similarly small)

Regards,
Thorsten

[dlparisi]

Using a vrayLightMtl results in the back faces being completely black. It does however fix the problem of flipping faces during DR but I'm stuck with pure black faces now in some spots. "Emit light on Back side" doesn't help either with that.

What I don't really understand in my setup is why it's just the DR nodes that are flipped and not the local ones - kind of seems like a bug to me.

[dlparisi]

Did you try raising the Secondary Ray bias (to 0.002 or something similarly small)

Yeah I tried that too - no help.

[Neilg]

Using a vrayLightMtl results in .

I said vray material, not light.

[dlparisi]

I said vray material, not light.

But them I'm stuck adding in either dome light or other lights to get the white parts to show up since there's no self-luminance in the standard vray mtl. Not exactly what I'm shooting for since I just want to accentuate the recesses in most places.

[MoonDoggie]

Standard Material, set to 2 sided option, diffuse->VRay dirt
100 self-illuminated,

and don't render with GI/lights does this work?

-Colin

[dlparisi]

Thanks but that's exactly the setup I have above which leads to the flipped faces.

[vlado]

What kind of geometry are the problematic objects? Do they have any modifiers?

Best regards,
Vlado

[emptyvoxel]

I often have this problem too, and I've found it's because of flipped normals. The only solution I know is to flip the faces or give them thickness, like with a shell modifier.

Does seem like a bug with the dirt material to me too...

~Michael

[dlparisi]

The geomertry is linked from an autocad file. In the acad file it's a region (a 2D planar area) so after linking it's not really defined in Max since it just says "linked geometry". It behaves basically like an editable mesh/poly and that's what I usually just add on top of the "linked Geometry" to make any edits. In this case though there is no modifiers on top although I've tried "Normal" (tried both check boxes), and putting an Edit Mesh as well. Both with no luck.

[vlado]

Well, beyond that it's hard to say without the actual scene to look at... if you can send at least a part of it to vlado@chaosgroup.com I can check out what is wrong.

Best regards,
Vlado

[dlparisi]

Sent. Thanks.

[dlparisi]

Vlado: Just checking to make sure you got the email. Have you had a chance to look at it if you did?