Insert knot - same control points different curve?


often I run in the situation that I add knot to a curve and the curve looks kinky. Than I create a new curve based on the control points of the kinky curve and than I got what I want - I can move the new curve control points and the curve stays smooth. So, finally I have two different curves with the same control points - one smooth and one with a kind of kink. Why is the curve with added knot not smooth? How to avoid the “kink” behavoir?


Here I moved the same control point of both curves to better show the difference

hi, might be a degree or weight difference. did you check those?

I found no difference. Here an example file.

KinkyCurve.3dm (697.9 KB)

The black curve has different knot values than the red curve (this can be seen by selecting the curve and running the List command). This difference in knot values influences the shape, because the knot values determine the speed at which the curve parameter changes as the curve is drawn by interpolating the control point positions.

OK, so we no the theory behind. So stay the question how can I avoid this issue and add a knot to an exist curve so that it looks like I had created it with the knot?

I think by running MakeUniform on the curve you can make the knot distribution uniform (i.e. with the same knot value difference between each control point pair).

What I don’t understand, however, is that the shape of the curve changes. The InsertKnot command should never change the shape of the resulting curve.

often I run in the situation that I add knot to a curve and the curve looks kinky

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Thank you Menno, MakeUniform solves the problem.

The questions is, why this command is needed? Shouldn’t the inserted knot work like I expect it? Is the current behavior useful?

I didn’t explain it right, it’s kinky after I start to manipulate the curve.