my mental ray doesn't like me... help please

Krisonrik

I was modeling this car that I designed and I used sub-d. Here comes the trouble... when I render it with Maya Software renderer, It looks fine. But when I try to use mental ray render, you can see the edges of the model has very screwed up edge (as I marked on the images). Please tell me how to fix it... thanks in advance.

fogmann

I believe it's because mental ray has some troubles rendering SubD model that doesn't originate from all quad mesh. You can either refine subdivision and then try, or just use polygons instead of SubD by applying poly smooth to low poly model, or alternatively, convert the subd to poly and then render.

Krisonrik

doh... doesn't that defeat the purpose of sub-d? I mean the partial increase and full crease are what made sub-d so unique. Any other way I can get that HDR image lighting effect out of other renderers? I mean Mental ray has final gather, but maya software doesn't. Anyway to get around that?

fogmann

Well, the geometry needs to be tessellated (converted to triangles) before it is rendered, and each renderer has its own way of tessellating geometry, so that's why it happens. I think you should be concerned with nice renders once you're done modeling and at that point you can fix the SubD surface so that it's possible to render it. It's not the reason to five up on mental ray. Here's what Maya help has to say:

[ QUOTE ]

Maya’s subdivision surfaces are supported in mental ray for Maya as long as the base mesh is made up of only quads.

The support for subdivision surfaces includes hierarchical edits, hierarchical material assignments, edge and vertex full creases only, uncreases, texture reference objects, deformation motion blur, and derivatives (for bump mapping and texture filtering). Unlike Maya, however, mental ray for Maya can handle only quadrilateral base meshes (a number of Maya standard subdiv shapes are therefore rejected), and UV coordinates can only be specified on the base mesh (level 0).

To get quads everywhere in a rejected subdivision surface

1. Select Subdiv Surfaces > Collapse Hierarchy > [ ].
2. Set Number of levels to 1.
3. Click Apply.



[/ QUOTE ]
And then render. Undo when you're done to get back where you were and continue working if you're not done modeling. Otherwise, you can just duplicate the SubD and collapse hierarchy for rendering, in case you want to keep your uncollapsed mesh around. Or go to Modify > Convert > SubDiv to Polygon [ ] and just render the mesh as poly - it will keep the look of all your creased edges in high poly (level 2 or 3 in convert settings) mesh.