Just thought I'd tell everyone we found no fix as such, but someone else on the team has the pro version of SketchUp and that has the export options we needed.

I don't understand the incompatibility between all these programmes but at least I have my problem sorted.

Maya hates double faces. I don't know any modelling programme that likes them. There's meant to be an option to remove them but it's not working. I'll go to their forum or maybe PolyCount and see what can I find out. I'll let you (and the world) know when I know.

I've never had much of a problem with ngons in Maya or UE4, unless animating (and of course UE4 will triangulate on import, but it seems to do it well). When I triangulate in Sketchup, unless this is a mistake I'm making for having done it so many times with so many settings, it seems to make far more triangles than necessary. One time I had it in Maya with about 20K tris, and now after triangulating in Sketchup it's 60K. Now, this could be for the error of the doubled faces, and the fact that I don't think at that time (when it was 20K in Maya) I had the faces with holes appearing. If that's the trouble then Sketchup's triangulating fine.

Whatever happens I'll post back here. And something will happen. I'm working on this since January and it's for a game I'm making, so I'll have this sorted one way or another.

Thanks a lot, my friend. I'll have a go from the Maya side of advice. I don't think it's a bug, though. I've always been warned against modelling faces with holes. I just thought that was for when a model would deform in animations, but it seems that was a misconception on my part.
I'll talk to them anyway, and if it's a bug I'll find out.

Thanks for all your help.

If I export single-sided as .dae Maya just almost can't even reckon the model (portions of it don't display depending on the camera view, and I can't check at the moment but I believe that was one of the settings that had Maya import single faces as tripled and quadrupled causing Z-fighting all over it), and of course the faces with holes don't import, as you'd expect. If I try to open this single-sided file in Open3Mod it gives an error and won't open it.

They're all doubled, and they display funny (I'll describe that in a second), so when I tell Maya to display face normals it appears as though every single face, including those that shouldn't be, has its normals facing outwards.

The first image is the way the .obj file looks normally in Maya (once 'display face normals' is on).

The second is what happens once I click on the model.

The third is what happens once I deselect the model.

The fourth is what happens once I move the camera in any way, reverting it back to the way it looks in the first image.

Now, what's happening is every face is doubled, and the face that's immediately visible is facing the correct way, which I found by deleting faces and watching the normal indicator disappear, whilst the doubled face is orientated the opposite way, as if to represent what in SketchUp is by default the blue material.

Wow, it certainly helped. Thanks.

So, now in Maya, all faces with holes appear, but every face in the model is now doubled. I have to tick 'export two-sided faces' in Sketchup or it won't load in Open3Mod. Does Sketchup always export the faces doubled or is this another importer problem? If so, perhaps I ought to find a Maya forum.

Thanks. Here it is.

Thanks, I've downloaded that one now and it's lovely.

Any advice in that case on getting this file into Maya or UE4 looking the way it does in Open3Mod? (I'm really, really happy that it's not exporting the way I thought it was, you've no idea.)

EDIT: Hadn't realised this thing was a converter as well. Trying that now.

Thanks very much.

What programme is that? I can't get it into Maya or UE4 without looking like a right mess. But the exporter says no-thing about it.

About the ngons, how do people normally do windows? especially rounded ones?