Zbrush -> 3dsmax -> zbrush = broken UVs

Coding
#1

Hey guys!

We’re having a problem when transferring OBJs between zbrush and 3dsmax, where sometimes the UV coordinates end up broken.

The symptoms of the problem are as follows:
[ol]
[li]After exporting an OBJ from zbrush into 3dsmax and back into zbrush, the following message appears: “Mismatch points-order in the imported mesh was detected and auto-corrected”.[/li][li]Now when looking at the UVs, the Tverts are still in the right position, but the faces have a different corner-vertex order. (see image: http://imgur.com/RmuAk)[/li][li]When comparing the two OBJs, it turns out that the file exported from 3dsmax has the right vertex-Tvertex-pairs, but the corner vertex order of the faces is different. (see screenshot from diff: )[/li][/ol]

I assume that during “fixing” the alleged mismatching point order, Zbrush changes the vertex-Tvertex-pairs, which messes up the UVs. This happens very infrequently apparently and I haven’t found a lot of information online about this issue. We can make a script to fix mismatching OBJs, but it seems like a bug to me that rarely happens, so I assume there’s a way around this.

Btw: when doing the same thing with Zbrush and maya, the corner-vertex order stays the same within the OBJ and after importing into Zbrush.

Have you encountered this before and know how to avoid it?

Cheers!
-Sascha

#2

That was quick. :):
One of our artist knew this issue already.

Turns out that through converting the object to editable_mesh and then back to editable_poly, right before exporting the OBJ from 3dsmax, fixes the problem and the faces’ corner-vertex-orders are just like in Zbrush.

:):

#3

That’s interesting. I’ve had very similar problems when trying to export UVs to import to pre-sculpted models in Mudbox. It sounds like Max is somehow reording the Tverts. Sounds like a bug in Max. Perhaps it might be worth reporting it to Autodesk.

I’m surprised converting the model to poly fixes it. I’d have thought that would be more likely to mess it up.