Bug Rhino7 Mesh.CreateBooleanIntersection

Rhino Developer
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1

Hello

I came across what appears to be a bug in Rhino.Geometry.Mesh.CreateBooleanIntersection. I am running the attached Python code on the two meshes in the attached file. One of the meshes has two vertices very close to each other at a distance of about 0.08, this is correct.

MeshBoolean200321.3dm (39.5 KB) MeshBoolean200321.py (791 Bytes)

import rhinoscriptsyntax as rs
import Rhino
selectedA = rs.GetObject(‘mesh a’,32)
selectedB = rs.GetObject(‘mesh b’,32)
for offsetX in [0, 200, -200]:
if offsetX:
meshA = rs.coercemesh(rs.CopyObject(selectedA,[offsetX,0,0]))
meshB = rs.coercemesh(rs.CopyObject(selectedB,[offsetX,0,0]))
else:
meshA = rs.coercemesh(selectedA)
meshB = rs.coercemesh(selectedB)
booleansAB = Rhino.Geometry.Mesh.CreateBooleanIntersection([meshA],[meshB])
booleansBA = Rhino.Geometry.Mesh.CreateBooleanIntersection([meshB],[meshA])
print offsetX, ((‘AB closed’ if booleansAB[0].IsClosed else ‘AB open’)if booleansAB else ‘AB failed’)
print offsetX, ((‘BA closed’ if booleansBA[0].IsClosed else ‘BA open’)if booleansBA else ‘BA failed’)

In Rhino 6, all booleans fail. In Rhino 7 curiously, I get the following result:

0 AB open
0 BA failed
200 AB open
200 BA failed
-200 AB closed
-200 BA closed

The same applies if done manually in Rhino 7: If I copy or move the objects by -200 along the x-axis they boolean fine, otherwise not.

As it might take time to fix the Rhino code, is there any quick fix I can do, such as rebuilding the mesh or similar? Thank you very much!

3

Hi @Ano,

As you assumend, this seems to be a problem with Rhinos internal MeshBooelan Code. Curiously running _MeshIntersect on your two test meshes yields a perfect closed Curve lying on both meshes, so its quite wierd thast the boolean fails. I Tried this in R6, definitely something for @piac to look at as an example for his rewrite of the Mesh Intersection code.

To maybe fix your immediate problem in the meantime:
Since your meshes are rather simple, I would convert them to Polysurfaces via the _ToNurbs command and do the boolean operations on those, as that code is more robust. You can then make a Mesh out of the result again via _Mesh

image
image1382×723 37.9 KB

1 Like
4

Hi Chris @Ano

yes, there’s no new code for MeshBoolean in V7 WIP, yet – it’s the same as in V6 right now. The commands that have new code are listed on that page.

I created report RH-57533 so that this does not get lost.
Thanks,

Giulio

–
Giulio Piacentino
for Robert McNeel & Associates
giulio@mcneel.com

1 Like
5

Hello Lando and Giulio @lando.schumpich @piac

Thank you for looking into this. The other ugly thing I did was moving my geometry around by random vectors until it found a position where it worked.

@piac, it does not seem to be true that V7 uses the same code as V6. In V6 the booelans always failed, in V7 they sometimes work.

Best,

Chris

6

Oh you are right! I think the previous team added some tweaks to make it more robust. It’s still the old code, with some tweaks.