Intersecting surface problem

Two surfaces clearly seem to intersect, but won’t trim one to the other. Any ideas?

IntersectProblem.3dm (95.0 KB)

Hi Cairn,

One surface has a degree of 7 in V direction
If you rebuild that to be a degree 3 the intersection goes all the way.

Still this looks like a bug.

Also @pascal I like to report a bug in the rebuild tool with this surface.


they do not fully intersect afaics, when you extend the cutting surface on the bottom by 1 it will trim/intersect.

I disagree:
Increasing the isocurve density, clearly shows they do interscect beyond the point where the intersection was found

right. but it still trims when you extend, problem solved, at least i hope so. rhino generally has problems with intersections, not going down a bottomless rabbit hole. also sometimes geometry may be slightly wonky, difficult to say.

also one should not have to rebuild constantly, changing input geometry just for tools to work is a no go when i think about it.

Yup, thanks all. the Extend trick is another workaround. The one I used was to create a trim curve, and then the surfaces join just fine.Def a bug not to find the intersection

Another workaround is to change the model tolerance from 0.001 to .0005 just for the _Intersect.

Yes you seem to be right, but take care as I have run into glitches in the past when changing tolerances while modeling…

Yeah, this looks like it needs a tune up. For now, extending the linear surface first gets the right curve-


RH-65567 SSX: short


how did you create the trim curve then?

This seems to happen from time to time (even with clean and relatively simple surfaces) for no apparent reason.

yup, unfortunately it fails pretty reliable on simple conjunctions like these where 2 pipes with the same radii meet each other.

No problem with these two…

torus_intersection.3dm (522.0 KB)

I’d assume this depends on tolerance settings

maybe, but messing with that does not always help.

I moved the 2 surfaces and discovered that picking them in the same order but in different locations for _Intersect can produce different results. The GIF below shows a result of 3 curves and another of 2. Why do selection points matter for an SSX?


IntersectProblem_MovedSrfs.3dm (104.4 KB)

rebuild the smaller surface :wink:

This script creates an intersection that can be used to trim both surfaces:

Ah, blended from the end of the intersection curve and a line known to be tangent to the surface edge… :grin: