SurfaceEdges with multiple curvepoints after splitting it with a line

Hi all,
I have an issue here. When I split this surface with a line, the surface edges behave kind of strange.

The result is gonna be a curve with 4 controlpoints.
I am familiar with all principles that Rhino works with, but I am asking myself how that can happen as the surface is planar and the curve I cut it with is linear.

The solution of course will be to project the curve to the surface and then trim it with it. And that’s working fine.

This is kind of strange, because in some cases it works, in some it doesn’t.
Is that some kind of setting I made or is that just the way it get computed and I will not be able to control that?

Thanks in advance

What degree is the line and how many control points does it have? You can check it using the What command.

My guess is the line is degree 3 with 4 control points. Try changing it to degree 1 with two control points, untrim the plane, and then redo the split or trim.

It looks like the degree and number of control points of a split or trimmed edge depends on the degree and number of control points of the trimming line or curve, though not always quite a directly as might be thought.

Yes, I already did check the properties of the curve…

Valid curve.
start = (49280.832,-74922.397,0.000)
end = (50828.453,-58831.962,0.000)
domain = -2295.101 to 13869.590
line length = 16164.691

So this seems pretty okay-ish, right?

I tried it again and it’s very strange.
The lines are 100% lines and not nurbs curves or polylines
See the result. I really do not know what’s happening here, as I’ve done that plenty of times so far.

Can you upload the .3dm file with geometry which does this.? Either drag the file to where you type your post, or click on the vertical arrow icon above where you type your post.

@davidcockey here you go!
TestSplit.3dm (48.9 KB)

Hello - I do not think this has ever been different - v5 behaves the same way with these. Can you describe why this is bad?


@tobias.stoltmann I am now as confused as you. You can always use Rebuild, or ChangeDegree with Deformable=Yes to convert the degree 3 curve to a degree 1 curve with 2 control points.

@pascal - okay. I mean it seems sensible.
I am using these curves to process them and therefore they need to be lines. The strange thing is it has never happened before or at least I never ran into that problem before.
Oh yes, that’ll do!

Thanks you all. :slight_smile:

Hi Tobias - once you have the curves, SimplifyCrv will make them into lines if they are linear.


It is seemingly inconsistent, though I know Rhino does not have a random number generator controlling results.

I’ve done some experiment splitting planes with lines. The edges are sometimes degree 1, sometimes degree 3. I’ve tried but cannot determine the determining factor. If it is important one of the developers will need to look into it.

Hi @pascal,
okay. Thanks for your and @davidcockey’s help.
Our team just decided that in the future we will just project the cutting edges before processing the surfaces.