Why does Maya LT create alternate UV sets? How to stop?

[javor_alex]

This is an issue I face on almost every model I create but I cannot find an answer to. 

I unwrap and layout the UV's for a model. I start by making a camera projection of the entire model, then individually cut out the shells. I do this the same every time. Usually I assign material ID's per mesh island, but most of the time the entire model is with one material. 

After finishing the layout, exporting as FBX, and importing to Substance Painter, I usually realize that some parts of my model belong to a second UV set, and I have to return to Maya to sort that out. And it's not easy to sort out either. I cannot figure out what is the default UV set : diffuseUV or uvSet1? It seems whichever is the extra one somehow always gets created and random parts of my mesh get assigned to this alternate UV set. Sometimes all I have to do to solve this is copy the UV's over to the original set, but other times, like today, while I am still working in Maya the difference between the sets causes my geometry to explode and the program to crash. Today I lost 5 hours of work and I want to leap headfirst out of the window. 

Sorry, had to vent. Is this a workflow mistake I am making? I've read all of the documentation, and I still can't make sense of the UV sets, how they get assigned, etc. Any help is majorly appreciated.

[javor_alex]

Further troubleshooting : 

Here is the crux of the issue. 

There is two UV sets. I believe one is default created by Maya, and perhaps the second one is coming from Zbrush? On the currently selected mesh, it's not a problem because I can access both of the UV sets, as you can see in the picture above. So I can select the UV's and copy them to the other map. No problem. 

However, if I select any other part of the mesh, I only get access to one of the UV sets at a time. I simply cannot copy the UV's to the other set. I cannot delete either of the sets either, leaving me with only one. 

[sean.heasley]

Hi @javor_alex

UV sets shouldn't be getting created randomly. By default they are only created when transferring UVs to another set for something like light maps.

You may want to check your workflow and/or hotkeys to make sure you aren't accidentally creating another UV set.

Also, when you go to UV map you can check your UV sets and make sure there aren't any other maps hanging around so you can work solely on your UVs.

That said, if this occurs again or you have steps to reproduce this issue please let me know!

[sean.heasley · Accepted solution]

Hi @javor_alex

Just saw your other post. Zbrush is most likely the culprit with the second UV set however you should be able to transfer the UVs from one set to the other and then delete the Diffuse UV set since the map1 is the default set that can't be deleted.

[javor_alex]

That would make sense, but I am not doing any UV work in Zbrush whatsoever. However, exporting from Zbrush does assign a new material ID, so maybe there is some kind of exchange happening in there that is messing things up. 

Anyway, although I am not sure exactly how to keep this from happening in the first place, I have developed a way to easily segregate and delete that unwanted UV set. For whatever reason, if I select the meshes that have the alternate map01 set, the default diffuseUV set does not appear in the UVset Editor, so I can't copy and paste. However, if I just combine all the meshes into one, then I can copy their UV's and delete the extra one, then separate the mesh parts back out. 

[sean.heasley]

Hi @javor_alex

Wow that's a pretty interesting workaround. Are you using the color painting at all in Zbrush? If so it's possible that's what's causing the second uv set to be created.

If not, it may be an odd change with Zbrush causing this functionality which sadly I can't fix.

[javor_alex]

No vertex painting with zbrush. I am only subdividing to create a sculpt for baking, but the only thing happening to my original export from Maya is that the vertices get moved around some. 

Parts of the mesh do carry texture maps that I had assigned earlier in Maya. Perhaps Zbrush is re-configuring these somehow, breaking the link in the FBX. In the future, I'll try assigning a default Phong material to those parts so that they don't carry the textures into Zbrush and see if that helps.

[sean.heasley]

Hi @javor_alex

That's most likely the cause so yeah I'd recommend having only the default lambert material on the character before exporting.

[buunpde160503]

I have this same problem lately so I did some experiments and I think I figured it out.

If you import a model that already has UV from Maya to Zbrush, when you bring it back to Maya, the UV Set name will change from "map1" to "diffuseUV". This is the default UV set. The second UV set called "map1" was probally created when you transfer UV from the original mesh to this new one. Since the original mesh's UV set name is "map1", the naming mismatch happens and Maya will create a new UV set in the new mesh.

To solve this problem, you can delete all the UV before exporting the mesh from Maya to Zbrush, then undo to get the UV back.

Another solution is to change the new UV set name back to "map1" before transferring UV so Maya wouldn't create a new UV set.