Hi,
Is it possible to create a curve using this tool but lock certain points that the curve should always go through when modified?
I am connecting some points with a smooth interpolate point curve, but for example if i want to insert an extra knot to add some detail and i want all my other points, which i have manually clicked, to keep position. Otherwise i always have to do it over when something is modified…
Thanks
Hello - no, at least I can’t think of a good way to do that with a single curve.
-Pascal
Thank you for reply.
I noticed that in rhino during the input of interpolated curve the knots are created where you click but once you finish the curve is transformed into “curve through point” with control points and the curve completely forgets about the points it is designated to be passing through.
What is your opinion about this? In my opinion there should be an option in rhino to have it the way autocad has it, which is more logically expected behaviour for “fitting curve through points” and its possible further modifications.
Try turning on EditPoints…
It is a really good question. grasshopper provides two curve method. “interpolate curve” by definition must go through all control points. “Nurbs Curves”, on the contrary, usually doesn’t go through control points. But in some case, control points are on nurbs curves. As I know, where curvature = 0, and at start and end point of a nurbs curve.
I usually increase a knot weight to pull curve close to a control point. Changing knot vector should also do similar work.
I feel ashamed, Yes thats exactly what i was looking for and it even works when you insert extra edit points. i was confused because Pascal replied it is not possible and I did not know edit points were different from the points which are displayed when clicked on the curve
Thank you
Well you need to remember that the edit points are really a sort of artificial construction and the ‘real’ controls of the curve are still the control points. Also, if I remember correctly, the edit points may not be exactly where the points that you clicked on to create your interpolated curve - depends on the degree and the number of points… If you move one edit point, the curve still passes through the other edit points - however that does not mean the curve has not changed between the other edit points.
This is what Pascal was explaining - you can’t really edit a NURBS curve locally and not expect it to change further along - all that depends on the curve degree and the number of points etc. In the situation of your first post, what I would do is split the original curve somewhere on either side of the control point you want to edit, then edit the middle split section only. Then try to merge the edited section back into the original curve (match first). That’s the only way I know of to edit a section of a curve without affecting the rest.
You also might want to read up on how the different degrees and spans of NURBS curves work, and how far along a curve each control point ‘controls’…
