Reverse Subdivisions not working on meshes with UDIMs


Great app!
I can’t reverse the subdivisions on meshes with UDIMs it seems. After deleting the UVs, everything works perfectly. Other meshes work without problems.

The UVs needs to be reversed as well, are they the product of a subdivision as well?
If so you can send me the mesh and I can take a look.

It’s the Character Creator 4 standard geometry but subdivided in ZBrush. Then I brought it over to Nomad and tried to reverse subdivisions. Didn’t work until I deleted the UVs. Here is a link to the file.
Hope that works!


Yes, that’s because zbrush merges the UV during export, and it makes the UVs unreversable strictly speaking (not an UDIM issue).
If I try with blender (subdivide 13k->3.4M and export to OBJ) I don’t have the issue and reverse works in Nomad.

Nomad “reverse” algorithm will fail if the UVs cannot be reversed exactly.
For example if you take the default 98k sphere in Nomad and unwrap new UVs, it won’t reverse.

But with Blender or Zbrush “reverse” algorithm, it will work because they allow themselves to modify the original UVs. It can break the original UV though (in the example where the UVs were computed directly on the high res).

I’ll see if I can do something about it.

If I use Separate on your mesh, it’s interesting to see that both canthus are not exactly the same since their number of UVs differs. And so, one can be reversed correctly and the other cannot.
One has the same number of UV and position, but the other for some reason has a seam somewhere.
Canthus.obj (1.6 MB)