Oh I see, but then if the rock or lattice are rendering black it means there is no texture on the rock or lattice, so even if you boolean with it, the cut edges will render black. 

The best idea then is to have the same material on the rock or lattice as you have on the terrain you're trying to cut into.

For the lattice and for the terrain the 'set to solid' option is in the terrain editor, which you access by clicking on the E, and then on the little black arrow on the top right corner of the "terrain canvas".

Plus the terrain must be set to positive and the rock or lattice must be set to negative, then group.

Measure your mind's height
by the shade it casts.
Robert Browning (Paracelsus)

Fran's Freestuff

http://franontheedge.blogspot.com/

http://www.FranOnTheEdge.com