If I right click on the sample-line and choose "sample line group properties" it comes "material list" than I would like choose the exist ground and roadmodell-terass. But I can only choose exist ground why?
I was having the same problem--only the existing ground surface was an option in the Compute Materials dialog box.
It's possible you did the following:
created a corridor -> created a sample line group -> created the corridor surface -> attempted to compute materials
You should have done it in the following order:
created a corridor -> created the corridor surface -> created a sample line group -> attempted to compute materials
If you created a sample line group before creating the surface, try deleting the sample line group and recreating it. That worked for me. I can now select my corridor surface in the Compute Materials dialog box.
I thank the other posters who emphasized the importance of sample lines.
I'm not sure if this is a recently added feature since the majority of this discussion has taken place, but when I have created a new surface or pipe network, etc. and need to add these objects to my existing cross sections I do the following.
Select Sample Line > Right-Click Sample Line Group Properties > Sections Tab > Sample More Sources... (button at upper right corner of window) > all available sources should be listed on left side of window > select desired surfaces or objects from Available Sources and click Add>> to include in Sampled Sources.