Hi Stefan,

So here's a little setup that combine HF and COPS (Heightfield and image compositing).
I tried to add comments here and there.

The sub-d import method is probably overkill, especially if you want to get very dense detail.
I'm pretty sure it's possible to export an .igs nurbs surface directly from Houdini (but not with the apprentice :S). I will have a look at it today.

++