Getting BIM data into Unity (Part 0 - Introduction)

This post reflects on work that I carried out, elaborated during my guidance of a few Master thesis students, to better integrate BIM models into Unity.
This will be a multi-part post. This makes each article a bit shorter to read, but allows more in-depth information overall. Hope you like it. Please comment with feedback and further improvements.
Basic methodology
Unity can import geometry from FBX and Collada (DAE) files primarily. There are a few other formats, but these are the preferred ones. When integrating CAD or BIM files into a realtime environment, you have to convert the geometry.
During my Unity teaching and the writing of the book Unity for Architectural Visualization (buy from Packt), I’ve come up with a basic diagram explaining geometry exchange between CAD and BIM software and Unity.
Throughout these posts, we’ll go more into detail. We start with ArchiCAD, but will tackle Revit in a follow-up post. Promised!