Rhino V-ray render black spots

[LCSarch]

I am trying to render a simple box or any geometry(polisurface not mesh) in rhino using V-ray, but for some reason when the scale of the box is "small" the rendering shows black spots at random places sort of the kind of black spots you see when you render two overlaping surfaces.
The box is only composed of 4 surfaces, no overlaps, simple as it gets. So there shouldnt be a reason why this would happen. When I increase the scale of the box like 400% then the rendering come clean.
Does anybody know why that would happen? does V-ray has a setting that changes the scale of the grain or something like that? Or does it has to do with the scale of the object?
any help welcomed.

[dalomar_cg]

Re: Rhino V-ray render black spots

Okay. I've been able to reproduce it here. It looks like its not a V-Ray issue as much as a rhino issue. If the object you're trying to render is smaller then the tolerance of you're file, then Rhino will have an issue trying to mesh the file. Since V-ray is working of the mesh that Rhino calculates, if there are issues with that, then vray can't do its thing.

Check your unit settings and make sure that you have that setup correctly. Alot of architects (which I'm assuming you are from you're avatar...sorry if thats not the case) tend to model in feet. Well if you want something to be accurate to within 1/16th of an inch (which I know is asking a bit much for the built product, but for modeling is good) then you will need a very high tolerance (something like .000001). By default Rhino's tolerance is between .01 and .001, so making small objects compared to the units has a distinct possibility to be smaller then that tolerance. So change units into inches and your tolerance to something respectable (I personally keep mine at .0001, which is a bit on the high side). As long as your model is within that tolerance, then you'll be fine.

[LCSarch]

Re: Rhino V-ray render black spots

Thanks. That helps alot. I am an architect. I have a question though, (since it is the first time I deal with tolerance). I am working in meters, and I see under document properties/units and tolerances model units showing meters then "absolute tolerance" of 0.01 and a "relative tolerance" of 1.0 I was wondering whats the difference between the two. When I change both or either one to 0.00001 nothing happens. also when I zoom in close the whole display is jagged-up, the forms are basically undistinct. I change from meters to millimeters and the same thing persits its all wacked!

[LCSarch]

Re: Rhino V-ray render black spots

ok, i am working on meters, so I scaled the object by 1000 and the changed the units to millimetes without scaling it again, and then changed the model back to meters scaling it, and it seems that that fixed the problem. It think it has to do with AUTOCAD 2007 and how it exports to rhino.
any other suggestions welcome.
L

[dalomar_cg]

Re: Rhino V-ray render black spots

Check this page out...and while you're there check out the loads of other stuff on the Rhino wiki

http://en.wiki.mcneel.com/default.as...olerances.html

[Micha_cg]

Re: Rhino V-ray render black spots

I'm not sure I understand the whole problem, but for better meshes I would use the mesh settings. The tolerance settings are used for modeling issues only or?

The simpliest mesh settings are anything set to 0 and play with distance edge surface. This is the maximum error between the NURBS and mesh. Other seetings canbe add for fixing mesh problems.

I think, Rhino works best, if you try to keep the numbers of your units in a range of 1..10000 or something.

[Travis Serio_cg]

Re: Rhino V-ray render black spots

actually as a tip for the render meshes. If you are using Rhino 4 you can set everything to 0 and Density to 1. Density will generate Quad Meshes instead of triangles which generate lightning fast and render super smooth.

[dalomar_cg]

Re: Rhino V-ray render black spots

I'm not sure I understand the whole problem, but for better meshes I would use the mesh settings. The tolerance settings are used for modeling issues only or?

Its not an issue of mesh settings, but whether that mesh is smaller then the tolerances of the file. If the meshes are smaller (and chances are if the object is right at tolerance, then the mesh will be less) then Rhino can't export the scene correctly.

[Micha_cg]

Re: Rhino V-ray render black spots

Thanks Damien, good to know.

@Travis: can Vray handle quads or do it triangulate it?

[LCSarch]

Re: Rhino V-ray render black spots

Yes, it is obiously an issue of the mesh in relation to tolerance and importing something from Autocad 2007 because when I scale the object up like 1000 times the rendering comes fine, its how rhino reads the CAD imported file as something minuscular. I will keep on playing with it.

Thank you Mr. Damien.

L.

[Travis Serio_cg]

Re: Rhino V-ray render black spots

Thanks Damien, good to know.

@Travis: can Vray handle quads or do it triangulate it?

It works great, vray loves them.

It's all I ever use now. occasionaly ill go even finer by setting density to 1 and max distance edge to srf at around .002. Give it a try. I think you'll love it. All of my default templates now use Density .4 to do design and 1 to render. It's rare that I have to bump them tighter.

[Micha_cg]

Re: Rhino V-ray render black spots

Thank you, I will try it.

[Micha_cg]

Re: Rhino V-ray render black spots

actually as a tip for the render meshes. If you are using Rhino 4 you can set everything to 0 and Density to 1. Density will generate Quad Meshes instead of triangles which generate lightning fast and render super smooth.

I try to get quad meshes only today, but dosn't seems to work on this way. The meshing is very fast, but there are triangle meshes too. Did I something wrong?

[dalomar_cg]

Re: Rhino V-ray render black spots

That will have Rhino generate mostly quad meshes (maybe all quads depending on geometry). There is nothing in Rhino that will force all quad mesh generation (hence the lengthy discussions on the Rhino Newsgroup), so just try to get as many quads in there as possible and go from there.