Interpretation of Surface Intersection

Rhino Rhino for Windows
1

Video illustrates the challenge of interpretation by Rhino 7. It is causing a mess because parts are not intersecting as intended.
I am not sure if this is a tolerance issue, but any guidance in resolving this would be helpful.
TIA,
Darron

2

Hi Darron - can you please post a file with the two surfaces?

-Pascal

3

Rhino 7 issue - Intersection Interpretation - 121921.3dm (42.7 KB)

Pascal,
Thanks for the reply, see attached.
The scale of the surfaces are small, but necessarily so to accomplish our goal.
thanks
Darron

4

Hi Darron - I am not quite sure what I am looking for here - the edge of the purple surface seems to be not on but within tolerance of the green one, and the edge of the small triangular surface is essentially identical to the edge of the purple.

What intersection are you looking for?

-Pascal

5

What I’m struggling with is the difference between the result of ‘intersecting’ and ‘pulling’. When I intersect the blue/purple and green surface I do not get the same result as when I pull the edge of the blue/purple surface to the green surface. The variance is small, 0.001", but due to the angle of the surfaces connected to it things are thrown off heavily… nothing will join, trim, etc.

Is the 0.001" what I should expect as within tolerance? If so it will create quite a headache.

thanks

6

Go to Options>Units>Absolute tolerance. No feature should be smaller than 10 times the tolerance. (0.001 is generally good enough.)

Your surfaces may have bad edges. Use RebuildEdges command to fix the edges.

Another common problem is working far away from world origin (0,0,0). (Rhino cannot handle objects which are far away (millions of units) from world origin.)

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7

Hi Darron - set the file tolerance to .0001 and try.

-Pascal

1 Like
8

Pascal,
The tolerance solved the issue. With file size larger than 1GB I hesitate to do this regularly but expect bumping it to 0.0001 for these small entities, and then returning to 0.001, should suffice.
Thank you for your help
Darron

9

Hi Darron -

Changing the tolerance back and forth while modeling is generally a bad idea. You might get the intersection that you need at that point, but downstream operations might fail.
-wim

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10

Thanks for the feedback, that’s a good thought.
I may still do this, but will ensure that I join the surfaces with potential issues before reverting back to the lower tolerance. Not a perfect solution but may be needed with the large file sizes I’m using.
thanks
DR

11

Hi Darron - the problems will arise if the edges that join at .001 are no longer in tolerance at .0001, and need to be for some reason, so finish the job with tolerance at the larger distance.

-Pascal