Line despite being snapped to surface corner refuses to Intersect

what is wrong with the end of this drawn line, using line tool.

Running intersect, all lines bat two ends showed intersect, one did after a resnap, this one however refuses, despite turning on edit point, and snapping the edit point to the surface corner.

on a side note…I need to make a solid of this, an interesting corner shape formed from how a semicircle intersected with a curving partly flat surface will cause trouble no doubt. making a slid into a fine tip.

RefusesToIntersect.3dm (86.8 KB)


Geometry that shares a point may or may not intersect, it’s more a philosophical question than a math question…
Why your straight edges are composed of multiple segments?

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Well that is not correct.

should this declare intersect to be ok for creating surfaces ?

so far this item has shown naked edges and I cannot get rid of them, that corner is one !

I thought it was necessary to be sure all lines that meet do actually meet before using them for sweep etc.

Else naked edges nightmare occurs, and behold :slight_smile:

Straight lines were in fact one shape, a straight line, intersecting another surface.

nothing like a surface to add in some extra points !

If I de-point them I might get a naked edge on that surface, I’ll take a look.


Or, back here on planet earth, having all those points in your trim object is what is causing you problems. Look, if you untrim your surface, and use the KeepTrimObject=Yes, and then turn on your points for your trim curve, you get this:

Have you noticed this pattern where people are constantly saying your geometry is sloppy and needlessly complex? This is exhibit A. This should be a surface with two trims - one at each of those rounded corners.

The fact that you have so many segments in your lines means that anything you do with this surface (sweep, loft) will be needlessly complex as well. And so on and so fourth. Let me demonstrate - my version of your surface is on the right. I do a sweep1 around it, and it creates 5 surfaces, with breaks where you expect them to be. I do the same with your surface on the left, and it creates 12 surfaces. There is even some teeny tiny sliver surfaces for extra slop. Do you know what this means? It means the surfaces you are using to intersect/trim your surface are sloppy as well. This means when you to offset your surface or, or fillet the edges, or do anything similar, it just going to compound the mess you have.

So, to answer your question:

Sometimes. If your geometry is clean. Which yours is not.


FWIW, here’s what my surface looks like with it untrimmed, and the points turned on for the trim object:

The intersection is now fixed for v6.

That item , lets call it internal wall , IW1 was the result of simple surfacing cut into by another very simple surface, why it developed that measled mess is beyond me.

the following steps ideally require an image and a file, but until I get time for that, and working until 5am disallows just now, one can see that I used simple procedures. If things go measled everytime a simple surface from simple lines intersects another simple surface, is that me or rhino ? Only by stepping though the method used will we see where it went wrong.

  1. draw 4 lines and 2 corners using tan tan circle. result our back face edge call it Rail1a
  2. Post a thread on how best to find exterior tangent line on a 5mm dia pipe command made U shape, use result from answers for rail 2a, i see that InterpCrv projected onto pipe in top view gives the same curve so do that.
  3. create internal of that tangent on pipe line. using InterpCrv project method,… result rail 2b
  4. create a 5mm inset version of rail1, call it rail 1b
  5. create internal surface IS1 using NetworkCrv on rail1b and rail2b, line tool lines for the profiles at knots on start and end of corner curves between these.

Create a shape which is the curved front of this item, using line and circle tool.
Extrude that to make a surface. S1

Intersect S1 with internal surface IS1 to get front of this IW1

Select Rail 1a and Rail 1b and use planar surface command, get surface S2

Put lines (line tool) between S1 and S2 and perform sweep2, or I might have used NetworkSrf, probably sweep2.

I am a bit surprised that the result has developed measles.

As such I had not got as far as examining those lines as I didnt expect a mess.

I then selected this solid and ran Untrim command, it asks to select an edge, it wont let me.
select solid again and try for UntrimAll, item becomes deselected and asks for selection of faces, select all the faces, hit enter, nothing happens. KeepTrimObject=Yes each time.

What is wrong with my use of untrim, or untrimAll ? Preselecting or selecting after command makes no difference.

If I get time I will post the actual item in a step by step way to see just why basic simple steps create a mess.

does that mean there was a bug ?


I don’t think you can make such judgments…

The process you describe seems convoluted, involving projected and intersection curves.

Untrim works on surfaces, not on polysurfaces.

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Yes, there was a bug in that you came across a case that our code that intersects curves with trimmed surfaces did not handle. When the trimming is noisy and the intersection with the curve is not truly inside the active region of the trims, we have to do the best we can to think of all the ways this can happen, and write code to deal with each possibility. Your example is one that wasn’t handled, and hasn’t shown up as a problem until now. Thanks for the report.

Uhhhhhh no, what you describe sounds anything but simple. I can assure you, the five steps you outline sound like madness.

When you get a chance, post the file…