Cleaner trace curves

The tools used are Curve, BlendCrv and CurvatureGraph. 
You'll see BlendCrv initially tries to  go to the ends of the
curves but you can pull the base control point  back along the
curve to any point that looks good, and adjust the other  points
to make a nice looking blend.  At the end I compare it to your
curve which is a little lumpy for  building clean surfaces.

Pascal Golay pascal@mcneel.com www.rhino3d.com

http://screencast.com/t/cwpZxZ5lmH8