Placing control points equal either side of a mirror line

Hi Rhino Users, A bit embarrassed in asking but I am wanting to make a nice curve that the control points are of equal spacing in X and Y on either side of a center line. imagine a horseshoe line with a a center line through it. Just want want symmetry of points on both sides of that verticle center line. The way I would do it is set point in one direction. Then manually measure them in the other. Am I wrong in that method? thanks and Merry Christmas! —Mark

Could you include a picture or the file itself? I’m not quite clear on what you’re trying to accomplish. If you don’t want to share your file or show it you could maybe create a simplified example showing your problem/question.

Yes sorry of course a picture is needed. It is aligning the control points both horizontally and vertically to the coresponding one on the other side of the center line. Set point does the horizontal part. Just wondered about the distance part from the center line. thanks,Mark

Create half the curve. Line up the top two control points at the same height. Mirror the curve. The top two control points at the same height will insure tangent and curvature continuity. Join for a polycurve, or Match with the Merge option for a single curve…

Another method.

Mirror the entire curve with Copy+Yes

TweenCurve with Number=1 and experiment with MatchMethod

Rebuild if the result has too many control points.


Thanks David, I will try that.

Hi Mark - just in case it helps, there’s a ‘CurveSymmetry’ script here:


Hi Pascal, I loaded some of your scripts.I also tried the one I needed and it worked very well. have a great Christmas!—Mark

You can make one half of the curve and then use Symmetry command to finish the curve.