4. Is that ArchiCAD terrain scaled to meters? I'm getting these weird circles all over it. And it looks like it's rotated 90° too. Making this program compatible with all these different OBJs is going to be more difficult than I thought.
Yes, meters, so the circles will be your rayepsilon being too low. ArchiCAD terrain (topography) is very large polygons (might be 10m x 5m x 7m).
It's not rotated, but in a different axis system. ArchiCAD, Revit, Inventor, Rhino, plus anything else that design people use have the Z axis up/down rather than the Y axis. I have worked out how to convert the translation and scale parts of the transform between the 2 axis systems, but not been able to convert the rotation part.
Potentially the easiest solution would be to have a "Z axis is up" checkbox when you load an obj - then have you code generate the transforms accordingly. So for Z up, you need to generate in the X/Y plane, but pack the transform in the Octane (Y up) axis system.
If you want to test this out....download the ArchiCAD 16 demo (you can install it and run it in demo mode where you cannot save a scene), then download the OctaneRender for ArchiCAD demo, and you can export topography, generate your transforms and load back into the plugin to render and test. What works for ArchiCAD will work for the Revit and Rhino plugins.