Drape question

Hello all,

I am very new to Descartes, the version I have is SS5, I have point cloud data of a railway cutting with a tunnel and I'm attempting to drape an element on to the surface. The thing is I have been given all of the point cloud data on one level and cannot separate out the vegetation. Hence when I drape I get tree lines mixed with terrain.

My question is can I drape from underneath to get the profile of the ground?

All the best,

Michael