Refitting to a specified number of control points


#1

Hello to all.

When working with computer generated coordinate data, the resulting curve often does not make good geometry. ‘Refit to tolerance’ is effective, but I would like to know if I can ‘refit’ to a specific number of control points. Is this possible?

Many thanks.


(Pascal Golay) #2

Hi Steven - use Rebuild for that.

-Pascal


#3

Yes! Many thanks to you Pascal


#4

With permission, I’d like to revisit this topic.

If I use the ‘Rebuild’ command on the imported ‘Before’ curve, the result does not match the original curve at all.

Just looking at it, I know I can manually trace the curve in 4 coordinate points and get very close to the original, as depicted in the ‘After’ curve.

I’d like to know if this manual process is automated in Rhino in some way; that is:

  1. Command Rhino to rebuild a curve in ‘x’ number of points.
  2. Observe the result of Rhino tracing the curve with the declared number of points, adjusting the weight of the coordinate points as/if required, knowing the result will not be an exact match.

Many thanks.


(Pascal Golay) #5

Hello - Rebuild makes a curve with evenly spaced control points - there is no calculation that I know of that tries to jiggle the curve to meet the input. I don’t say this is a bad idea, but I would be surprised if anything automatic could make anything close enough to what you want as a final curve to be worth it - i.e. you’d still need to adjust. With so few points it’s hard to see how you would save much effort in real life… my 2 piasters worth.

-Pascal


#6

Many thanks for responding quickly. It’s most appreciated.

I was just going to append the post to say I know of the ‘Smooth’ command, but this does not fit the ask.

Super computer generated data looks like a saw blade under Rhino curve analysis. By tracing to an extremely close approximation, I actually best the originals results, but I’ve been wondering if the process is automated in some way. Refit To Tolerance is an aid, but the imported curve must be converted to a Rhino native curve first.

Your put is appreciated Pascal. Many thanks to you.


(Pascal Golay) #7

Hi Steven - if you want clean curves for surfacing, refitting is not the way, I would say- you’ll get a non-uniform curve out the other side, often if not always. Rebuild to the structure you like or draw a new curve. Rebuild is really about getting the degree and point count you like - it’s less about shape, so consider it a new curve, I would say, that has nice parameterization.

-Pascal


#8

I agree with you Pascal, and again many thanks for your feedback.

Even through the use of RefitToTolerance, manual correction to final is still required to make the ideal aero surface sent to a machine.

This at least proves my search within Rhino is time not wasted.

Many thanks for your prompt and detailed feedback.