Visible seam in displacement with Mental ray – Tutorial
Number of people ran into this problem where you notice a tear in the displacement when rendered with mental ray.
If you take a closer look at the render you will notice that this tear appear at the UV border edges, and that is due to the fact that the sub-division approximation is smoothing the UV brooders, that’s why the displacement edges don’t match anymore.
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To fix this problem we need to disable this new method of approximation called the CCmesh, by running this MEL command
addAttr -ln “miExportCCMesh” -at bool mentalraySubdivApprox1;
where “mentalraySubdivApprox1” is the name of your approximation node.
However this comes with price, the CCmesh is much faster node to render and once you disable it. You will get a hit at render time.
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July 10th, 2009 at 6:47 am
HI, when i use the line of mel
addAttr -ln “miExportCCMesh” -at bool mentalraySubdivApprox1;
the next time i render, it appears to have disabled the smoothing so it renders the displacement map on my unsmoothed model, then if i uncheck the attribute and render again the smoothing is back on but with the visible seems again. I tried it on a plane and it worked fine. Can you think why this might be happening on my mud box model.
cheers
July 10th, 2009 at 7:59 am
Yes, this MEL will disable the CCmesh. as long as your approximation node is called “mentalraySubdivApprox1″
check the name of that node on your model. and make sure its the same. you might have it called “mentalraySubdivApprox2″ or 3. depending on your scene.
July 17th, 2009 at 11:21 am
can this also be overcome by leaving the ccmesh active and using the “smooth uv’s” option when baking in mudbox? will they smooth in the same way so as to line up? I’m going to give it a whirl i had a mesh with this issue a little while back, ill post back.
July 17th, 2009 at 12:05 pm
Unfortunately these are 2 different algorithms. You would still get the seams.
August 21st, 2010 at 9:49 pm
Hey, i found a pretty annoying but effective workaround for this problem, if i take my lvl 0 mesh from mudbox, export it to maya and smooth it to the correct subD to match my uvs in mudbox then use this smooth mesh as the target when exporting displacements from mudbox, it uses the smooth uvs to generate the displacement
August 27th, 2011 at 1:56 pm
Hi this command don’t work for me
I am rendering with MR too
// Error: Found no valid items to add the attribute to. Got a small displacement seam on my mesh. Help me if you can please ?
August 29th, 2011 at 2:49 pm
Sometimes the copy and paste can be wrong
try typing the actual command on your side
March 14th, 2012 at 10:24 pm
Works great! The only thing that I needed to change from the copy/paste was the quotes (“” instead of “”)