Thanks for your tip, I'll go into it and try.
On the other hand I would like to add those details to the skin of the heigthmap itself...

I fixed the link in the second question.

(somehow I can't get the img-tag working in my posts)
[img]http://www.stadrhenen.nl/beeldbank/main.php?g2_view=core.DownloadItem&g2_itemId=902&g2_serialNumber=1[/img]