I seem to be having some trouble getting a MeshOutline of quite a few terrain meshes that have come across from sketchup - is it just my Rhino? Silhouette seems to pick up the edges still.
Yes, that definitely looks buggy to me… You have some non-manifold edges in there due to one overlapping face, but even removing that doesn’t help. Splitting it into the disjoint pieces doesn’t seem to help either.