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creating tangent elliptical surface with two different shaped sections (rhino 4)


Hello all.

I really hope someone can help me for rhino.
I am creating a helmet or dished styled shape from three curves.
1.The outer perimeter is a rhino ellipse (labelled base ellipse in images)
and I want the helmet form created from two different shaped sections going along the
2.major axis ( section 2 in images)
3.minor axis of the ellipse. (section 1 in images)
With clean geometrical transitions in between.
I originally modelled using patch command, which gave fairly please results, but the surface was never tangent to the base ellipse.
I then rail revolved the minor axis along the base curve, to get one section nice, switched views and turned on control points on either side of the surface to eye up the section for the major axis. This worked pretty well but left me with a crease in the surface when I went to analyse it. I then chopped the crease out either side and blended the surfaces together, pretty pleasing result but again i loost the tangency of the base ellipse right on the side ob the blend.

I am sure the is something i am missing. I have also tried dividing into quarters and network surfacing, but that leaves me with more creases and an uneven surface.

Any suggestions would be amazing.


Here are the direct links to the images