FBX Import - Missing Tris - Maya

Hi all,

Ok, this is a really weird issue, I will be posting in the Maya forum also, but I’m hoping that perhaps someone here may have experienced this and be able to give me a point in the right direction.

In Maya I’ve created a cube, 1x1x1, then scaled it 1200x800x20. Added subdivisions, 60x40 - so it creates a nicely chopped up large flat rectangular object.

Switching to vertex mode and enabling soft selection, grab some verts pull them up, push some down - the object here is to create a piece of tileable seabed.

All good so far, no problems.

Exported as an FBX, all the usual settings I’ve used for other imports into Unreal. Everytime I import it there are random tris missing from the geometry, on both the top and bottom of the object - although not lined up.

Initially I thought this was going to be flipped normals, but I’ve checked that and its fine.

Through a lot of testing, the only thing that I can do consistently which seems to cause it is the soft selection tool - if I don’t use that, no problems.

Another fix, seems to be setting the object to be triangulated on the export. If I do this, the object appears within Unreal absolutely fine.

I’m not entirely certain what’s going on here. This is a very simple object, with very simple geometry. Nothing is overlapping, or poking into another part, in fact, using the soft selection tool raised/lowered the underside in symmetry with the top side, so nothing was getting pinched. I’ve used the “Clean Up” options to look for problems with the geometry in Maya, no problems found. I’ve done a merge on the verts in case for some reason there was some broken geometry, nope, not at all.

In Maya it looks perfect, imported it becomes swiss cheese - there are no ngons.

Any one have any thoughts?

Please be aware, due to being new here I am currently under moderation and my replies to your replies will be delayed - sorry :frowning:

Thanks in advance for your help/suggestions :slight_smile:

(I can’t seem to add any images, probably locked down because I’m a new user).

Maybe it is some tris this is inverted on your model


i have the same problems on some meshes with morphs. Its a unreal import bug. Cause UE4 Triangulate the mesh too if it is quad and there the devs made some convert bugs. So to stay on the save side. Always triangulate the mesh by your self in the scene befor export it.

I thought that might have been the case initially too, but the geometry appears correctly in Maya, it’s also been checked, cleaned up, and had various other things like merges done just to be sure there’s no rogue verts…

The only thing which seems to be consistent is the use of the “soft selection” tool. If that isn’t used, the problem doesn’t seem to occur. Equally, if the mesh is triangulated as part of the export, it doesn’t occur either.

Best guess at the moment is that the use of the soft selection tool places some normals in positions which Unreal Engine is having problems with.


Thanks for the reply.

Yeah, the triangulating before-hand makes sense, although mildly frustrating that, in this specific use-case that has to be done and not in others.

Out of curiosity, do you know when the assets would be normally triangulated by the engine? Is this upon import, or, is this as runtime?

If the latter, than it would invariably make a lot more sense to do this as part of workflow from Maya. If on the import, it doesn’t really make much difference (other than to fix this problem) - from what I can tell, e.g. I’m not saving the engine any work that really matters.

I’m guessing it’s probably on the import, as then it would only need doing once, not everytime the game was run.

Yeah i know your frustrating. Its a real pain. And its of course by the importing procress. To triangulate it per runtime would not make any senses :slight_smile: