...there is a Google Earth to C4D plugin available, quite reasonable priced..

http://www.archiplug.com/EN/GETerrain.aspx


Maperative is a free solution based on OpenStreetsMap

http://maperitive.net/

provides 3Dexport to .cae (Collada)

3dm wise..there is a rhinoplug

http://www.rhinoterrain.com/

imports all sorts of things..DEM, Pointclouds, Google Earth..but really a bit of an overkill for just 1 or 2 projects..