Mental Ray Rendering Problem - Please Help

[JPollack]

For some reason mental ray started acting screwey: It was rendering fine until I tried to change the material of a polygon, then all of a sudden when I rendered it, a bunch of the materials had switched, despite their accuracy in the actual model. Within the model itself, all of the materials are correct, and it looks fine. I even turned mental ray off, rendered it in Maya Software, and they're all right that way too. It's only when I render with Mental Ray that the faces reference the wrong material, and I have no clue how to fix it. I don't use render layers, and I know there aren't two surfaces on top of one another.

 

I've uploaded an image that shows a frame rendered in Maya Software, with a small region (in red) rendered in Mental Ray.

 

I'm trying to render an architectural model for work, so if anyone could help I'd really appreciate it.

 

Thanks

[shaneis]

Duplicate the model and apply Lambert1 (default lambert). Then re-apply the materials to the appropriate faces. You shold also select the polymesh and then check the hypershade to see which shadingGroups are applied to it Make sure to disconnect any unneeded shadingGroups (including lambert1).

 

NB: I'm assuming that the offending faces are all part of the same mesh.

 

PS: Hi, and welcome to CGA, fellow Maya user.

[JPollack]

shaneis,

 

Thanks for the help, I was worried it would come to that. I was hoping there was a quick-fix, like a maya equivalent to an AutoCAD purge or something. I guess I'll get to work going through the surfaces and updating the shaders

 

You were spot on that all the faces are part of the same mesh. I've been trying a new technique by working with imported Sketch-Up models, and haven't quite figured out how to make the objects come in as separate elements.

 

And thanks for the welcome. I'm actually the only person at my 75+ person firm who uses Maya, which sucks because I don't really know anyone that knows the program as well as I do. You can bet I'll be on here next time I get stuck.

[HamburgerTrain]

Aren't they just lamina faces? If you just merge all verts then do a cleanup on the mesh with "lamina faces" selected, Maya should delete the overlapping face.

 

It all depends on how well the model was drawn in SketchUp though. A program like Maya is very strict about polys wheraes I've found that SketchUp doesn't really give a stuff how the mesh is constructed, which causes problems in the rendering stage...as you've found out!

 

But like all programs sharing models with exporting and importing there is a lot of manual work involved in cleanup. But FBX is usually the best.

 

The program I use to draw the buildings doesn't have FBX export so I use 3DS...So after importing into Maya I use a little script that does this:

 

- Merge Verts

- Conform Normals

- Quadrangulate

- Merge Border Edges

- Delete History

 

I run the script three times...I don't know why three, but it still fixes things the 2nd and 3rd time round then I find I'm left with a pretty damn good model left. I wish I could write MEL but anyway, it works!

 

Hope that helps you out somehow!

 

Edit: If you want the model to come in as seperate objects, you might like to try doing it with material colours...say walls dark grey, glass light grey etc...in Sketchup. That way when you import into Maya all you have to do is select by material in the hypershade then break apart the mesh. That's what I do and it's very reliable that way if I use SketchUp to Maya.

Edited February 9, 2009 by HamburgerTrain

[Chog Burley]

i find using different materials on individual polygons within the same object really causes problems for Mental Ray.

 

try separating out the polys that need to be diffrent materials.

[Dragonearl]

I see another Maya user has found out that Maya likes to throw its toys out the pram for not reason at all

 

there may be an easy fix for this, give this try if you have not yet fixed it.

 

For some reason Maya likes to mess up its SG's and geometry. First duplicate your whole model and move this above your original, now combine both models together to form 1 mesh. Once you have done this select face mode and delete all of the faces from the duplicate mesh so now all you have left is your original model and then try rendering this.

 

With sketchup when you export make sure that you choose the options and un-check the double faces export as this will save you a lot of problems with overlapping and non manifold geometry.

 

I hope this works