Hello everyone.
I’ve noticed some UV bug when exporting hi-poly meshes (problem almost gone when exporting lo-poly meshes). For example, I created an object and convert it to hi-poly mesh. Then, I import exported object back into Rhino (or any other 3d software) and see some strange “stratched” verticles (hilighted lines) in the UV map.
Problem appears on both Rhino 5 and Rhino 6 beta.
Hi @k.lukyanov,
Are the UV’s correct if you save and load your model as 3dm instead of exporting + importing?
You used Unwrap to generate the UV’s right?
HI!
I should say, that when I unwrapping mesh created in rhino in other 3d-softwere everything in fine, even when I import unwrapped mesh back into rhino.
I would like to take a look at that model to see which part of the mesh those highlighted parts come from. Could you @k.lukyanov upload the file here?
I’ve logged this issue. It may be related to UVW map exporting to FBX.
This happens when texture coordinates are set on the mesh object using the custom object mapping. After applying texture this problem is visible already on the “Good” mesh object where the sphere bottom meets the box:
This becomes visible in UVEditor only after mesh is imported back to Rhino because at this point the custom object mapping needs to be re-created from the texture coordinates that are set on the mesh (texture coordinates are imported and exported but the custom mapping object is not).
Well, thank you so much for helping me figure it out. Now, when I apply texture I see this issue.
Hope, this bug will be resolved.
RH-32866 is fixed in the latest Service Release Candidate
RH-43051 is fixed in the latest Service Release Candidate
I’m affraid, that it’s not fixed 
Again, after export and import back in Rhino, some vertices at wrong places.
So, after a year and a half, I was able to figure out how to avoid this problem.
Let’s look at this step by step:
1. Create simple object (mostly this bug appears in spherical shapes)
2. Create custom mapping (I’ve unwrapped objects by cutting it every seam)
3. Create custom mesh and export it
4. Import back this mesh and check UV mapping
Now, you can see the problem.
From this point starts most interesting things…
I’ve noticed, that created UV island not matching mesh shape (before exporting).
So, I’ve decided to setup mesh settings in the preferences first.
Then you need to recreate your UV mapping and export mesh (this is important) with the same settings as the settings in the properties.
In the end we can have perfect UV map:
Summarizing all the above:
before we create our custom UV mapping we need to setup custom Render Mesh Quality in the Preferences and after that we need to create or export mesh with the SAME SETTINGS as the Render Mesh Quality settings in the preferences. After that no UV problem will be appears. Mesh displayed in the UV map should be identical with the export mesh.
I’ve re-opened the YouTrack item.
Hi @k.lukyanov, I’m replying to this rather old thread to inform you about the recent fixes in Rhino 7.
That’s correct. That is the best practice although we are trying to remove this limit.
As you also noticed the Unwrap command had problems uncoupling UV islands correctly - that has been addressed and Unwrap works more reliable in Rhino 7 SR3.
Handling of texture coordinates for OBJ and FBX export has been improved. But in many cases it requires the object to be re-unwrapped with the fixed Unwrap command.
One of the bugs associated with this topic: RH-43051 is fixed in Rhino 8 Service Release 7 Release Candidate. Please give it a try.
