basic: keeping outline of a shape at 0 height while soft editing surface?
ideally keeping it creased with the horizontal plane.
subd?
looks like a subd workflow for me:
left to right
draw initial curve
_planarSrf
_quadremesh, convert to Subd, interpolate
manual optimize the subd, edit it without editing the outer edges / CVs
if you want to do it with nurbs - it s hard to impossible to CV-Edit a trimmed surface.
- looks like your surfaces is a patch ?
what s the next step, what do you need the data for ?