Intersecting surface problem

[cairn]

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

IntersectProblem.3dm (95.0 KB)

[Willem (Willem Derks)]

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.

-Willem

[encephalon]

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

[Willem (Willem Derks)]

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

[encephalon]

@Willem

I disagree:

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.

[cairn]

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

[spb (Steven Burzinski)]

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

[cairn]

@spb

change the model tolerance

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

[pascal (Pascal Golay)]

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

RH-65567 SSX: short

-Pascal

[encephalon]

how did you create the trim curve then?

[norbert_geelen]

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

[encephalon]

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

[martinsiegrist]

No problem with these two…

torus_intersection.3dm (522.0 KB)

I’d assume this depends on tolerance settings

[encephalon]

@martinsiegrist

I’d assume this depends on tolerance settings

maybe, but messing with that does not always help.

[spb (Steven Burzinski)]

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)

[raba (Info)]

rebuild the smaller surface

[spb (Steven Burzinski)]

This script creates an intersection that can be used to trim both surfaces:
https://github.com/CADacombs/rhinopython/blob/master/xIntersection_surfaceSurface_PullTween.py

[cairn]

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