Surface Restriction
On the Surface Restriction tab of the Surface or Solid from Profile form, you can specify a Top and/or Bottom surface in order to restrict the upper and/or lower extent of the extrusion.
To ensure the validity of the operation, theses surfaces should: have been created using the DTM function; have similar extents; and should not intersect each other. No check is made that the two surfaces intersect.
Clip to Top and Bottom Surfaces
Select the wireframes that represent the top and bottom surfaces. Enter (or double-click (F3) to select) the Type and Name of the wireframes you want to use.