Rulesurf is good, but as you say, I'm still left with 3D faces, not a solid. I can extrude 3D faces into 3D solids but they have to be co-planer 3D faces. Rule surf produces 3D faces with four vertices which do not extrude. In order to get 3 vertice 3D faces between structure contours I have to do it by hand, one face at a time; or generate a mesh (which I do in SketchUp using the sandbox from contours command).

Let me ask the question in a different way. Is there a way combine a group of 3D faces that enclose a 3D space into a 3D solid? Say I created a cube using 3D faces. Could I turn that into a solid with newer versions of AutoCad? I guess I should talk to my AutoDesk Dealer.

How much does that Solid Works cost?

I've been playing with SketchUp to solve this problem. I took a polymesh representing a topography. I then placed a 3D solid cylinder that intersected this mesh. Using the Intersect With Model command I was able to create a cylinder that had a top that is topography. But when exported back to CAD, I have a set of 3D faces, not a solid. And I'd like to have a solid, because then I can use the slice command to create cross-sections that have a face along the section plane.

Still, the SketchUp approach worked pretty well. As the final product is a SketchUp presentation, I may just have to use SketchUp to create and manipulate my objects.

Thanks for your help, Tom.