Maya supports three types of geometry: polygonal (Polygon Mesh), free-form objects (NURBS curves/surfaces), and subdivision surfaces.
Free-form NURBS curves and surfaces in Maya are supported by mental ray for Maya. These surfaces, which can have a boundary and several holes, are expressed as trim and hole curves in the NVIDIA surface definition.
Maya polygonal meshes are exported as NVIDIA polygon objects and support features like vertex sharing, holes, and displacement refinement. Displacement mapping can be applied to meshes. The special displacement properties for polygon surfaces are controlled in much the same way as NURBS surfaces.
Polygonal meshes that consist only of triangles or quadrangles can be exported as a subdivision surface base mesh for mental ray rendering.
To export a polygonal mesh for rendering, you must create and attach a Subdivision approximation node to the mesh. This node lets you further control the subdivision process and quality. Additionally, you can create and attach a Displace Approximation node to support the displacement of the mesh.
If mental ray for Maya encounters a Subdivision approximation node, it is exported as a NVIDIA subdivision surface base mesh (including textures and motion vectors, but without normals) instead of a simple polygonal mesh.
If the conversion fails (because other than triangles/quadrangles were found), an error message is printed and the mesh is exported as usual.
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).