Trimming Curved Surfaces - Possible Bug v8 SR22

Rhino Rhino for Windows
1

Version:
Version 8 SR22
(8.22.25196.13001, 2025-07-15)
Commercial

Surface Trim Issue.3dm (177.1 KB)

There may be a possible bug or additional code that need to be implemented to make trimming curved surfaces actually work. Can someone tell me how to trim a curved surface in this file by simply selecting the cutting surface?

When trimming rectangular objects, Rhino works perfectly like this…

1-Trim with Rectangle
1-Trim with Rectangle523×406 10.8 KB

2-Trim with Rectangle Result
2-Trim with Rectangle Result407×368 5.2 KB

Now let’s look @ trimming this area:

3-Curved Area to Trim
3-Curved Area to Trim1173×585 22.5 KB

If I select the surface that will be the trimming/cutting object like this:

4-Object to Trim
4-Object to Trim520×421 12.6 KB

and select the object where the arrow is, NOTHING HAPPENS.

However, if I select the surface edge of the previously selected trimming object rather than the surface itself, the trim works perfect.

5-Select Surface Curve
5-Select Surface Curve678×484 14.6 KB

Why is this? It should not matter if I select the surface edge versus the surface itself. I realize that if I select a surface for trimming, Rhino might only trim if that surface is completely within another surface. Is this how Rhino is supposed to work?

If so can there be a feature request where if the edge of the selected surface is used for trimming and it’s against another surface then Rhino will trim the selected surface?

If not, then it seems like this is a bug.

2

Maybe it’s because the surface you’re trying to trim is totally mangled (look at the isoparametric curves and CPs)?

Skärmbild 2025-07-25 23.10.09
Skärmbild 2025-07-25 23.10.091920×1110 73.5 KB

3

If that were the case, then selecting the edge of the surface that I want to use as the cutting object wouldn’t work either because the edge is part of that trimming surface. Furthermore, selecting the edge of the trimming object works perfectly fine, so selecting the trimming object itself should work as well, just like it does with the rectangles.

4

As part of trimming the intersection between those two surfaces is calculated. In this case where those two surfaces meet they are tangent to one another. This is a known limitation for our intersectors and the calculated intersection can be incorrect or fail. I opened RH-89032 to get this fixed. In the meantime you’ll need to trim with that edge curve since it isn’t calculating the intersection between the two surfaces there.

1 Like
5

Thanks so much for your help!