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ZBrush <> Maya 2011 UV problem

ZBrush Usage Questions
#1

Has anyone run into this? I am making architectural models in Maya 2011, and texturing them in ZBrush. I am finding that about 75% of the time when I export an object from Maya to ZBrush the uvs are not usable and have to be remade in ZBrush.

When this happens I am stuck with a model whose texture can only be edited in ZBrush, as the uvs get tiled. This mucks up our pipeline as it renders the textures uneditable in Photoshop.

I have yet to find any consistency in when this happens, other than it happens when using .obj export, GoZ or .ma export. I suspect that something has changed in this version of Maya but need to test this hypothesis.

T

#2

Looking at this over the weekend I found at least one case where an object that is acceptable as a Maya or .obj mesh is not cool when brought into Zbrush, at least as far as the uvs are concerned.
When you combine more than one poly object together and export it, you will have an object that consists of more than one shell. This means that there are separate meshes within the object, and even though you may have acceptable uvs as far as Maya is concerned, Zbrush cannot handle them.

PS: After trying this a couple times I see a curious behavior. I can load the obj in, and put a texture on it, that works. I can go from texture to polypaint, but cannot go back from polypaint to texture. The uvs are still mucked up. You can see that by doing a texture from uv, so I have not solved it in every case yet.

#3

Thanks to Paul Gaboury at Zbrush Support for the solution to the problem. When I merged several objects into one, I merged the geometry shells into one, but the uvs were still in separate shells. These were overlapping slightly, and spanning the default uv range of 0-1. Zbrush needs the uvs to not overlap and span a range slightly less than 0-1, on the order of 0.001 - .999, so to that end I wrote a tool for Maya that merges the uv sets and scales them slighly.

You still need to combine objects into a single object, and use merge vertices to make a single geometric shell. I didn’t code these commands because the merge vertices command settings will depend upon the scale of your objects.

This is very simple and there is no error trapping, so use at your own risk.

///prep selected object for zbrush editing ///merges any uv shells, and scales uvs to slightly less than 0-1
$selected = ls -sl;
select -r ($selected[0] + “.map[0:1000000]”);
$selected2 = ls -sl;
polyMapSewMove -nf 10 -lps 0 -ch 1 $selected2[0];
polyEditUV -pu 0.5 -pv 0.5 -su 0.999 -sv 0.999 $selected2[0] ;
select -r $selected[0];
delete -ch $selected[0];