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Fixing Invalid Meshes in Blender

10

If you import models from external sources, you may run into the 'double face' problem, where three or four vertices don't define one, but two faces. Blender has no UI tools to fix this, but hidden in Python there's a powerful function to help you out. Daniel Salazar shows us how.

About Author

Bart Veldhuizen

I have a LONG history with Blender - I wrote some of the earliest Blender tutorials, worked for Not a Number and helped run the crowdfunding campaign that open sourced Blender (the first one on the internet!). I founded BlenderNation in 2006 and have been editing it every single day since then ;-) I also run the Blender Artists forum and I'm Head of Community at Sketchfab.

10 Comments

  1. This is the 'missing link' for the models that I have to import.... which show exactly this sort of behaviour. Previously I had to select the face(s) in wireframe mode, delete Only Faces then rebuild the faces using the F2 tool for speed. This tip will save me tons of time!

  2. Would recalculate normals then give the expected result once this command is given?
    And by the way, why on earth this command is not in the mesh->cleanup menu??

    • Yes and dunno, probably because this shouldn't happen. Do you have a simple test obj file that we could investigate? Also some people have reported getting this FROM BLENDER by using multires modifier.. it's kind of a mystery why this happens.

    • Nope. As shown in the video there are no overlapping vertices. There are though multiple faces generated by the same vertices. As to say, take four vertices and form a face, then take three of them and make another. Three other and make another. It sounds like crazy but it happens often with imported meshes. I have nightmares importing big files from nurbs software: often the tesselation process generates such situations. Can't wait to test if this command will solve those too

    • nah, they covered that in the video. the faces in question actually share all the same verts but likely just don't face the same way so since there are no duplicate verts to remove remove doubles doesn't do anything for this.

  3. Actually, there is a pretty bad condition co-planar face condition that can be created by accident within Blender. If one creates a triangle polygon using 3 out of the four vertices of a quad, then we have a condition of two absolutely coplanar faces sharing the same render plane in space. The render will, of course, show tearing and artifacts where the two faces are rendered. The Python command presented above will not detect this condition. In fact, I couldn't find any utility (within the interface) that would allow me to do so. Besides simple inspection (tedious), does anyone know how to fix such a thing automatically?

    • i don't know anything about fixing it automatically but unlike the full two faces sharing 4 verts like in this video mesh lint does find things like that since the edges and verts will end up being non manifold in that case.
      if you're in edge or vertex selection mode it will select the triangle face as well (because you've selected all it's sides/verts and you can just delete > face(s) to remove it it.

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