Summary: The CurveOnSurface plug-in allows one to draw a curve on a surface by specifying a sequence of points to interpolate. The resulting curve is later editable using these defining points.
The CurveOnSurface Plug-in provides two commands. The CurveOnSurface command is a proposed replacement for the InterpCrvOnSrf command in Rhino 5. The CurveOnSurfacePtOn command turns on control points to edit this curve.
Unlike the InterpCrvOnSrf the curve created with CurveOnSurface is independent of the parametrization of the surface. The curve will tend to go in a straight or direct path instead of following the surface isocurves. In fact, when only two points are specified the curve is the shortest possible path (a geodesic), the same curve made by the ShortPath command.
The CurveOnSurfacePtOn will turn on control points at the interpolation points that defined the curve. These can then be edited individually, or in larger selection sets, to directly edit the curve. The points will be constrained to stay on the surface. Control point editing commands such as Nudge may also be used. The PtOff command turns off all control points.