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On a mesh imported into Blender from a specific format with a conversion plug-in, I get duplicated vertices in the same positions, and the different faces of the mesh aren't connected to each-others.

As far as I can tell, this would be solved by the "Remove double" function, however using it deforms the mesh.

What can I do to merge all the duplicated vertices in the mesh, but without deforming it ?

(This mesh was under PMX format, in order to be used with MikuMikuDance. I imported it in Blender to rig it.)

Faces aren't connected to each others :

Faces aren't connected to each others

Normal mesh :

Normal mesh

Deformed mesh :

Deformed mesh

AlexAngc
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    Most likely removing doubles corrupts imported normals. If after deleting custom split normals and re-adding them with e.g EdgeSplit modifier object becomes the same then you can use that solution. If not then maybe manual cleaning will be needed. – Mr Zak Jun 07 '17 at 18:37
  • You were correct about the normals : deleting the "Custom split normal data" corrected the issue appearing with "Remove double"; however, the body edges that looked smooth now look sharp. I tried to use EdgeSplit like you advised but couldn't make any difference :-/ – AlexAngc Jun 07 '17 at 19:51
  • Ok this is quite confusing but simply pressing "Add custom normal data" solved the issue perfectly. I have no idea how Blender decided what normals to generate though. – AlexAngc Jun 07 '17 at 20:00
  • When I pressed the "Add custom split normal data" button I was expecting it to ask me for some kind of input, the fact that it restored the normals to their original "appearance" by itself is quite confusing. In any case that solved my problem, can you make your comment as answer so I can mark this question as solved ? – AlexAngc Jun 07 '17 at 20:11

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When removing doubles from the imported mesh the normals split in a custom way aren't preserved, making some dark patches to appear. Probably some of split normals were saved while others weren't because removing doubles doesn't choose to preserve given vertex just because it stores some custom data.

In anyway if removing doubles make sure to remove imported normals as well. That will make model lose its look as it was done before exported though.

If the lost shading is important and irretrievable possible solutions can be to manually join double vertices to control which vertex goes where (long way) or recreating shading as it was before removing normals (may be even longer).

Another way would be to duplicate the object before removing custom split normals, remove doubles, work with it and once done use Data Transfer modifier to copy normals from one mesh to another.

Adding another layer of custom normals with "Add Custom Split Normals Data" in the Geometry rollout can eliminate the problem but this solution doesn't seem to be stable as it works somehow differently for different objects.

Mr Zak
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  • I guess I was simply lucky that in my case, adding the default custom split normals data was enough to restore the original appearance. Thanks for the help ! – AlexAngc Jun 08 '17 at 12:04