QuoteIm surprised this software doesn't have native solution.
Well, this is primarily 3d terrain rendering software, I think the developers are wise to concentrate on that and not make it an all singing, all dancing 3d application. Personally i think the way to go is to render hard surface objects in Maya and composite with terrain renders out of Terragen - let each software do the job it's best at.
Actually Terragen at the moment forces you to load an .obj for a mesh and .chan for animation separately, and I prefer that as it enables an animation update with having to re-import the object over. Having said that though, Alembic import would ideally, be the way to go.
I think OpenVdb import/export for volumes is on the road map for this year.