Hi all this might have been asked, but I can’t find it in the forum after searched for an hour 
Can someone explain to me these weird accerlation bend, like the Maths reason behind?
They are not created by control point weight, which is the same
I understand knot and control point, and show edit point and remove knot doesnt help
I know the whole curve can fix by makeuniform, but how do you fix it manually on spot
Is it curve degree or something, or still something with knot? Thanks
How was the curve created?
Run the command List, select the curve, and post the results.
Or upload a .3dm file with the curve.
Sounds like a strongly non-uniform knot distribution (in parameter space) combined with the control point distribution. But without the curve or List results that is speculation.
test.3dm (78.4 KB)
I mean it happens all the time, not specific to this file.
I just never know how to properly fix the issue beside makeuniform
@lmnoc1 As I speculated above, the cause is a strongly non-uniform knot distribution (in parameter space) combined with the control point distribution. ‘MakeUniform’ will change the curve to uniform knots but also change the shape of the curve. ‘Rebuild’ also results in a curve with uniform knots but also changes the shape.
How was this curve and other similar curves created? Is it a segment of a larger curve?
Common ways of creating curves with non-uniform knots include:
InterpCrv or CurveThroughPt with option Knot=Chord or Knot=SqrtChord. Those commands and options result in non-uniform knots Usually don’t result in a curve such as the example without subsequently moving a control point.
InsertKnot. Inserting a knot will result in non-uniform knots but does not change the shape of the curve until a control point is moved.
RemoveKnot Removing a knot wil result in non-uniform knots. It would require removing may knots from a curve with uniform knots to obtain a curve with knots as non-uniform as the example.
Extracting an isocurve from or duplicating an edge of a surface with non-uniform knots. There are multiple ways surfaces can have non-uniform knots including Sweep1, Sweep2 and NetworkSrf.
Describe the steps which result in a curve like this, including any input geometry.
Thanks for the reply. Do you know can we manually edit the knot (which I know prob different from CurveEditPoints) besides insert and remove? like how can i visualize it when not in RemoveKnot mode and can I move the knot around to manually distribute them?
I think my question is less about the creation process, but at times of this scenario arise
how can i manually edit something rather than an automatic MakeUniform or Rebuild
There is something wrong in the curve creation process. I don’t know about boat and ship hulls, but in industrial design 3D surface modelling, you only ever need single span degree 2 - 7 curves, where you never fumble with weights, etc. at all. Normally, you start with a degree 2 curve, and then raise the degree, step by step, if necessary, to draw the intended curve as minimal as possible. Exception would be a blend, where you take an end-to-end degree 5 curve right out of the box, so to speak, because you need 6 control points.
Rhino cannot display the knots of curves so as to make them editable like the control points.
Rhino 9 WIP has a test command TestShowKnots which displays knot locations in curves and surfaces. Hopefully it will become a standard command. It can be very useful for more knowledgable users.
InsertKnot and RemoveKnot are the only tools In Rhino which I know of for direct control of knot locatons on a curve or surface. I don’t know of any tools which allow direct control of knot parameter values.
“Curve edit points”, also known as Greville points, are based on the knots but in general do not coincide with knots. They are used for editing curve shapes because they result in a diagonally dominant set of equations which are generally easier to solve and more robust than the equations resulting from using knots. However it is possible to use knots to edit points; however McNeel has not implemented that capabiliity in Rhino.
Rhino should implement toggling the display of knots (and other curve/surface properties) like in Alias, etc. In fact, an Alias-like “Control Panel” would be really good.
