#781 Two triangles close to sloped wall mangled on export to obj

[Stephen]

So I have a sloped wall at 45 deg. with two triangular fixed windows following the slope. The windows are close enough that the non-window part of the rectangle go beyond the wall slope. When exported to an obj, the area is hollowed out. This happens in both blender (the example screenshot) and in Unreal Engine. I also include a test file with a number of tests which was used to generate the screenshot from blender.

[Emmanuel Puybaret]

Thanks for your report and test file. I successfully tried the exported OBJ file in 4 other software : in Sweet Home 3D itself where you can import the exported OBJ file as a piece of furniture with the Furniture > Import furniture menu item, in macOS Preview application, in Wings 3D and in Autodesk FBX Converter.
So I fear it's a bug in Blender (and Unreal Engine) and it would be kind from you to report this issue to their teams. Blender generally imports well OBJ files, but I noticed on my side that some normals generated by Sketchup exports are sometimes wrongly interpretated (like in this example).
In the meantime, you have two workarounds at your disposal:

• import the exported OBJ file with the Furniture > Import furniture menu item in Sweet Home 3D, and export the reimported object to OBJ format again. From my tests, Blender accepts that second import better, but a few normals are not set correctly (but this can be fixed in Blender afterwards).
• import the exported OBJ file in Autodesk FBX Converter, export it to FBX format, and reconvert the FBX file to OBJ format again. This operation seems also to generate some normals that Blender doesn't interpret correctly but the shape is correct.

I keep this bug open in the hope you'll give some feedback once Blender and/or Unreal Engine wil have fixed this issue.

[Stephen]

Hmmm. Strange. Two different methods with two different outcomes for me.

• The furniture library round-trip worked to fix the holes. Of course this will kill iterative workflow if I have to spend ages to export the scene as obj, import obj to library, import library, place "furniture", export scene to obj, load obj to Blender/Unreal, and then potentially find/fix normals in a fairly massive model.

• I downloaded Autodesk FBX Converter, and followed your instructions, but I cannot import that double-converted object into Blender, getting a stacktrace ending = ValueError: could not convert string to float: b'-1.#QNAN0' Not sure why it worked for you.

When I find a moment I'll try raising issues for the original exported problem file with Blender and Unreal, and feedback if I get any response.