Hi. I am a programmer who has a day job maintaining a specialist 3D visualization application. I have a personal license for Sketchup Pro that I use for hobby work, and I recommend it to colleagues to use for quick 3D modeling.
Anyway, a colleague recently pointed out to be that selection behaviour in my software is different, depending on the export format from SketchUp: if they select a face on an OBJ model, then the entire object (of which that face is a part) is selected. This is the intended behaviour.
On the other hand, if they export in 3DS or FBX formats, which my software also supports, then selecting the same face only selects that face, not the entire object.
I investigated, and I discovered that SketchUp emits duplicate vertices for some export formats.
Take a simple example: create a simple cube in SketchUp (draw rectangle, push/pull into a cube, double click to make a group), then export to OBJ and also to FBX (both are text files viewable in Notepad++). In OBJ format the cube has 8 vertices, which would please my old geometry teachers. In FBX format the cube has 24 vertices. This is very inconvenient, since my app is designed to load HUGE models, so adding a step to weld vertices (which I have tried before to deal with bad models) is potentially an O(n^2) task (O(n log n) if I optimize) and adds a lot to load time.