Help needed with finding centre line through 2 curves

Experimental drawing.3dm (2.6 MB)

Hi, Could anyone advise on how to find the precise mid curve between these 2 curves?

Much appreciated,


First of all. select curves. Rebuilt it to some good amount of points. Loft two curves. Select Surface. Use command extractwireframe. Dis-select mid curve that you want. Delete rest. Delete surface and you will have the curve. Experimental drawing 1.3dm (44.0 KB)

Thanks, just tried that, got the mid line which looked ok then divided it into 10mm incriments and bisected it and the distances are not exact.

In Rhino for Windows I would use TweenCurves with the SamplePoints option. Does Rhino for Mac have TweenCurves?

It does but doesn’t seem to work for this task, at least I can’t make it work

Use _MeanCurve command instead TweenCurves.
Rebuild properly your curves is also a good thing to do.

Also just tried tweens for these curves. It’s not pretty, and sample point usually deviates from the original curves to begin with (same with rebuild). In my opinion refit should work but it’s ugly. I got exact results by first using fitcrv (to degree 3 angle tolerance 1) on each curve. Then tweening with refit match method.

Tween.3dm (74.5 KB)

again, un even results with meancurve method

Thanks Micheal, looks to be a kink in this area

Is there a kink? Looks like that is just the dimension line.

Your quite right sorry…cleans glasses :slight_smile:

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Not working for me for some reason, tween curves is giving all sorts of odd results

that which I sent was with tween curves. The process is as such.

  1. Use the FitCrv command on each curve - set to degree 3 and Angle Tolerance 1 (Make sure to delete original curves or put the newly fit curves on a separate layer so you don’t select the old curves on accident when tweening. )

  2. Tween the new fit curves using tween with settings of Number 1 and match method as refit.

That is exactly what I did on your file and got the results I posted.

still not getting exact results on putting a bisector line in.

Everything is depend on curves that you have. If you refined it enough, it will give you required result. TweenCurves was on my find, but I didn’t knew if it works in Mac or how much precision you want. So refine your curve. If I have to do this, I will do it in grasshopper to the extent of precision which is required.

Ok, i do keep rebuilding but curveanalysis keeps showing irregularities in the curves, how do i get them perfectly smooth?

Well averages of curves are not really an exact science. there is not 100% answer like say averaging some points. A lot has to do with curve degree, kinks, control point distribution, weights, knot vectors ect. So more than likely the results will always be an approximation within some tolerance.

Your curves have different control point structures and distribution as they are now. You could try to rebuild each to the same control point count (although this will change the curve shape to some degree) the more points you have the more accurate it should be.

Yes, and that’s why I mentioned grasshopper. I can divide the two curves in say 1000 points, then make a line between them and then find out there center and then interpolate a curve between them, I can increase this to say 10,000 in a click in grasshopper. So, it will be precise enough. But input curves has to be refined in first place.

Thanks for your help folks, would this be considered smooth enough?

Yup, try TweenCurves or my method. It should work.