Skeletal mesh importer cuts mesh over UV seams

Development Rendering
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1

Can someone confirm that the UE4 cuts skeletal mesh over UV seams? Why it does that and is it possible to avoid this problem?

A simple way to check it is to export a skeletal mesh from UE4 and open it in an external application, then you will notice that vertices are not welded on seams

2

Did you ever find an answer to this?

3

Still seeing this issue exporting from UE5.4 to default fbx 2013 and importing to blender and seeing the skeletal mesh torn along UV seams… If you do not fix this and reimport back into unreal you will then notice the normal distorted along the UV seam.

4

Actually you can kind of “fix” this in unreal with the reimport dialog and make sure to tick import normals and tangents instead of letting unreal calculate them.
Use this to force the dialog for import.

However this doesn’t fix the issue that unreal creates in an editor like blender or maya where the skeletal mesh is now needing to be rejoined by distance because its now torn along its UV islands after export to fbx. Sadly this all but destroys normals in some cases making it really difficult to work with any fbx exports from unreal.

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5

I’ll outline a little dance you can do to work around this until a fix is found.

Use gltf exporter for the skeletal mesh
this will preserve the mesh edges from being torn/ripped
then export the fbx and use the armature from it to reparent to the mesh from gltf exporter
because gltf import in blender and many other applications wants to adjust bone rotations instead of leaving them alone.
Reparent the working mesh from gltf to the fbx skeleton (using armature deform to keep current groups/weights) and test the pose/weights and reexport using fbx to go back to (UE4.26-UE5.4.1)

This issue doesn’t appear to happen in UE4.25 and below.

Cheers,

6

To circumvent this issue, I

  1. Double click the Skeletal Mesh to open in Editor and click the “Make Static Mesh” button at the top. Then save as a new StaticMesh.
  2. Right click the new StaticMesh and “Convert to Skeletal Mesh”
  3. Open up the new Skeletal Mesh in editor and click the “Editing Tools” button at the top.
  4. Click Mesh Processing>Weld.
  5. I put the “Tolerance” up to 100 and switch “Split-Attribute Welding” to “On Full Mesh”. then hit the “Weld Edges” [Accept] button below the model. ( don’t know if that make a difference or not, but that’s what I did.) You may need to lower these settings, i dunno.

And there, I now have a seamless Skeletal Mesh.

For some reason, “Weld” won’t work for me unless I do this ridiculous ritual…

Hope it helps.