I have run into a problem with exporting an object with changing topology, it seems to create unique faces.

When I export a static object and open it in maya, the normals are all as expected and it works well.

However, when the topology changes, there seems to be no way to import that fbx file (into either houdini or maya) with out the faces being unique. I can fuse and recalculate the normals in both packages but it gets quite slow.
(I have tried to fuse on import in maya and it crashes - that's another question for others later)

Is this a limitation of the fbx format?

MD

Is this a limitation of the fbx format?

Yes.

In fact, the FBX format doesn't support animated meshes with variable vertex count at all, only those where the number of vertices stays constant for the duration of the animation.

We, however, thought that it might be better to at least export this kind of geometry in some kind of form, and found a workaround which you have very precisely described.

Note that if an animated object has a constant vertex count throughout the animation, the FBX exporter will not triangulate and unique its faces, but will keep it “as is” instead.