As a follow-up, I did the 3DM > DWG > SKP route. This worked, but required a substantial amount of tweaking as follows:
The DWG files exported from Rhino could not be directly imported into SKP. They came in all wonky when they came in at all: geometry reoriented in different directions and other weirdness. Also many problems with non-closed curves.
Opening the DWG exports in AutoCAD and resaving them fixed that problem. Those resaved files import to Sketchup fine. However, Sketchup faceted all the curves with 96 segments each, something which I could not reset on either the DWG or SKP side. This multiplied the geometry so crazily that the resulting SKP file was 1.4GB. Not good.
The workaround was for me to go back into Rhino and use Grasshopper to divide all those curves/circles and then redraw them as closed polylines, essentially doing the SKP faceting by hand so it would turn out the way I wanted it to. It was a kludge, but it worked. All the circles were converted to 12-sided polygons, exported as polylines to DWG. Opening them in AutoCAD, I discovered that my closed plines had all been re-opened as part of the export, so I closed them all manually there and resaved.
Importing these files into Sketchup, I noticed two things:
- the reduction facet geometry dramatically reduced the file size (Yay!)
- The closed polylines are all exploded as individual segments (Boo!)
- The circle patterns I had done building wall face as groups in Rhino are all now reoriented in weird directions in Sketchup, despite being correct in AutoCAD (WTF?)
The exploded plines thing is a pain, but not a deal killer. The geometry reorientation thing is bizarre, but I can fix it since the circle/polygons have retained their relative orientation to one other by wall face, even if they don’t even remotely line up with the wall orientations any more.
So, that’s the rest … of the story.