Spherical mapping Nurbs + SubD render differently

I get different results when rendering in VRAY when i compare the render viewport with the vray render.

The nurbs (rectangle) shows the correct mapping in the render view, but in the vray render the mapping is incorrect.

When i try the same on a Subd plane (LH square) the renderview and vray render is correct.

When i convert that shape to Nurbs, the renderview and vray remains correct.

Whats going on the the Nurbs???

Hi @Tangers

Spherical mapping has discontinuity at poles. SubDs are rendered with fairly high tessellation and therefore discontinuities often show very small artifacts. A planar nurbs surface instead is rendered with a very sparse tessellation and therefore the discontinuity causes a very large artifact. When you convert the SubD into a polysurface the result will not be a single planar nurbs surface and therefore it will often render with denser tessellation which again makes the texture mapping discontinuity artifacts appear smaller.

Rhino’s Rendered and Raytraced display modes do spherical mapping per pixel and therefore tessellation density does not cause issues there.