Well, the house design is in Sketchup.   When I import the scp file, I get that single object, including the house itself, elevation, etc.   All I want from HD is to be able to landscape that design.  Because the scp file has all the elevation data and is viewable in 3D in HD, I wanted to just add plants and stones, etc.  Not start over with designing the house.  I'm guessing you can't place objects on that surface?