Hi Micha, for most mesh uses such as just rendering it for example, those "butterfly points" are not normally a problem, so MoI's mesher has not been designed to treat them in any special way or avoid them. They are not really what I would call an "error" in the mesh really.

But I would think it would be kind of unusual to get that situation, especially if you have a well formed fully closed solid it should not have any border edges at all in the generated mesh, so probably ensuring that all edges are joined and that you have a closed solid would be a good step to help avoid that kind of thing.

If you can give me an example that does generate one of those butterfly points, it would help me to understand the situation a bit more.

... Actually, if I understand the problem correctly, it may be that you have to avoid certain arrangements of geometry which are just not permitted by Unfold3D - for example how would you expect for me to avoid a butterfly point with a model that is set up exactly as the example shown in the Unfold3D page? I include an example file here - how would you expect for this mesh to be created without any butterfly points?

I suppose one possible solution is to have that butterfly point be a duplicated point instead of a shared point between the faces that touch there. Right now I have no provision for doing that, so if you need such a thing you should try exporting with welding turned off, then take that result mesh into a polygon processing program and weld all other points except for that butterfly point, that may eliminate it.

But it would probably be best if Unfold3D would just duplicate ("unweld") such points itself since it is sensitive to their presence...

- Michael