Problem EdgeSrf.3dm.zip (26.3 KB)
See subject.
The arc has a superfluous knot. Remove that knot using RemoveKnot (which changes the arc by less than absolute tolerance) or create a new arc which can be within 4.E-12. EdgeSrf using the simpler knot is a simple surface.
I don’t know why EdgeSrf created a polysurface witht the seam located at the extra knot in the arc. Probably something to do with how EdgeSrf handles input curves.
How would splitting a circle create knots?
You have a degree 2 curve, but with 5 CVs. The curve has a kink. Hence you get a polysurface. Check your curvature graph, very odd. How did you draw this curve? Better use proper NURBS curves.
Not sure exactly what you are asking. Every multi-span curve has a knot or multi-knot between the spans. Normally if you use Split to split a curve/arc the result is two curves, which can be joined into a polycurve.
Technically the curve has a multi-knot of multiplicity 2. In a degree 2 curve that is a fully multiple multi-knot which can result in a kink (discontinuity in tangency) but this curve is G2 continuous.
If an input curve to EdgeSrf has a multi-knot EdgeSrf creates a polysurface rather than a surface with a multi-knot.
Arcs in Rhino are proper rational NURBS curves.