Join and Match effects on knot vector

Rhino Rhino for Windows
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1

I just discovered that when _Join (or RhinoCommon’s JoinCurves) or a position-only _Match is applied to a NURBS curve with internal knots whose curve end point needs to be translated to match the curve to match, the internal knot values may change in the process. Case in point with
JoinSkewsCrvKnotVector.3dm (38.8 KB):

The knot vector of one of the NURBS curves is
Before join: 1 1 1 2 3 3 3
After join: 1 1 1 1.9999941914531612 3 3 3

Are there advantages in skewing the knot vector versus only translating the control point, thus maintaining uniformity?

_Rebuild can be used afterward to regain uniformity, but it may unnecessarily reshape the curve.

2

When yanking the end of curve A to match curve B, the closest point on curve A to the end of curve B is found. A is trimmed back to that point, and then yanked. The trimming changes the knot value at the end of A. The final step is to change the domain of A back to its original values. In your case, it looks like the start of your curve was trimmed off. Trimming like this prevents wiggles and hooks in many cases.