FBX export reverses normals with block symmetry



there is a problem with symmetric block instances

  • Make 1 cube and create a block definition with it.
  • Then use the _Mirror command on this block.

  • Export to FBX and re-import the FBX. We get this:

The normals of the symmetry block are reversed.

This is the exporter, because with FBX Review and Unreal engine, I have the same result.

(I use Rhino Version 6 SR14)

Thank you .

  • jmv

Not sure, the _ExtractRenderMesh has the same effect …

Hi @kitjmv,

Did I understand correctly that this works in an older version of Rhino 6? If so, which one? @tim Are you the FBX guy? I assigned the thread to you.


Hello @DavidEranen !

You put me doubt !!
That i know, (I built this scene visibly in March 2018)

Maybe I’m going wrong by saying 6. (12), but in this scene I have a lot of blocks and I had no problems.


Do not listen to me !!

@wim sent me the link to install Rhino v6.12.

the result is identical, the inverted normals on the symmetric block.
It’s surprising, but maybe I’ve never done symmetry on export blocks…


I need to look into this some. I don’t think it’s FBX export itself that’s the problem. If you make a plane and make a block out of it. Mirror the block. Mesh the results. Run SelMesh then Dir. You’ll see the normals are flipped there too.

FBX doesn’t export blocks or components or whatever they might call them. It exports the transformed mesh as an individual object. So what you see in the test above is essentially what FBX is using as geometry to export.

I’ll post here when I know any more.


I think this is a long standing bug with symmetry and it used to occur with mirroring as well. I have a custom view mode which shows backfaces and before I export I make sure all normals are pointing correctly. Try using the flip command on those symmetry objects and then see if the export works if not then there is something broken in the exporter.

Here is a YouTrack issue you can look at to track progress. As it stands now this will not be fixed in the V6 timeframe. https://mcneel.myjetbrains.com/youtrack/issue/RH-51561