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IDProjectCategoryView StatusLast Update
0003065PartDesignBugpublic2021-02-06 06:43
Reporterabdullah Assigned To 
Status assignedResolutionreopened 
Product Version0.17 
Target Version0.20Fixed in Version0.17 
Summary0003065: Part::checkIntersection returns false negatives preventing functioning of PDN Mirror transformation when faces just touch
DescriptionProblem 1

Part::checkIntersection first uses first_bb.IsOut(second_bb) for a quick test. However, this function is known to fail in cases of touching (there is even a previous comment in the code). Mirror transformation explicitly asks that touching to be considered intersection. Therefore it is wrong to rely on this test.

Problem 2

The Extrema method implemented in Part::checkIntersection fails:

Case 1: When mirroring a feature that just touches, it sometimes fails because BRepExtrema_DistShapeShape returns BRepExtrema_IsVertex instead of BRepExtrema_IsInFace, so the manyfold detection mechanism fails to identify a non-manyfold case. In one example, instead of InFace it returns 4 Vertex: [0, 5.5, -2.5], [0,5.5,2.5], [1E-15, 13, -2.5], [1E-15, 13, 2.5] for Support1 and [0, 5.5, -2.5], [0,5.5,2.5], [-1E-15, 13, -2.5], [-1E-15, 13, 2.5] for Support2. I am unsure if this can be somehow reused.

Case 2: When doing a multitransformation to create a part out of a quarter like here:

The extrema method provides a separation (notable, in the order of milimeters) in operations with intersection parts. This may be a consequence of which parameters we are passing the to function.


Some related problems not directly related to the extrema method, but that seem to be related:
Steps To ReproduceEXAMPLE 1

1. Load the attached file.

2. Activate the first body

3. Select the pad and add a Mirror transformation (you can try directly the mirror, or a multi-transformation, vertical+horizontal to see the different cases)


1. Load the attached file

2. Activate the second body

3. Select the pad and mirror or multi-transform mirror the pad
Additional Information
TagsMirror transformation
FreeCAD Information



2017-06-01 23:08


Helix_Mirror2.fcstd (17,168 bytes)


2017-06-18 03:49

administrator   ~0009441

@abdullah should this be resolved now that FreeCAD Pull Request 816 has been merged?


2017-06-19 12:49

manager   ~0009454

Yes, this ticket is to be closed as fixed by that PR


2017-06-19 17:12

administrator   ~0009459

Thanks! Closed.


2017-06-25 09:36

manager   ~0009522

Last edited: 2017-06-25 09:36

The boolean check method fails in some circumnstances where the extrema method success. For example:

The result is that "the shape does not intersect support" is generated, when the real problem is OCE/OCCT can not make a proper fusion of those valid and perfectly intersecting objects.

IMO it is not ok to inform that something that clearly intersect does not. So this is a bug.

The final outcome in these cases should be: no error because it does intersect, and a resulting bad solid because it is what OCC gives back. This can be solved by a three phase checking (instead of a two phase one):

1.Quick check
2. Extrema
3. If Extrema says it does not intersect (sometimes because of the non-manifold detection failure), boolean check.

In case of OCC>6.9.0, this checkIntersection, as well as all the fusing in PDN should probably be upgraded to use generalFuse (same as Part boolean fragments fuse).


2017-11-20 10:08

developer   ~0010435

Last edited: 2017-11-20 10:10

How about avoiding the check altogether? I.e., mirror, then fuse, then check the result of fusion (it should remain a single solid; if it doesn't -> show the "does not intersect support" message to user).

Another option is to drop the single-solid limitation altogether. Then, the check can also be removed.


2018-01-02 17:56

manager   ~0010674


Good to hear from you :)

What we have currently in master seems to work well. I am not sure if I "fixed" this, or what exactly went on (I can not remember).

I have just updated the target version to 0.18 to get it out of the 0.17 roadmap, as this is no urgent matter.

I do not close the ticket. I will eventually come back to this and assess it again.


2019-04-06 19:15

administrator   ~0013009

Changing ticket status from 'feedback' to 'assigned'


2022-03-03 13:55

administrator   ~0016539

This ticket has been migrated to GitHub as issue 5704.

Issue History

Date Modified Username Field Change
2017-06-01 23:08 abdullah New Issue
2017-06-01 23:08 abdullah Status new => assigned
2017-06-01 23:08 abdullah Assigned To => abdullah
2017-06-01 23:08 abdullah File Added: Helix_Mirror2.fcstd
2017-06-01 23:08 abdullah Tag Attached: Mirror transformation
2017-06-18 03:49 kkremitzki Note Added: 0009441
2017-06-19 12:49 abdullah Note Added: 0009454
2017-06-19 17:12 Kunda1 Status assigned => closed
2017-06-19 17:12 Kunda1 Resolution open => fixed
2017-06-19 17:12 Kunda1 Fixed in Version => 0.17
2017-06-19 17:12 Kunda1 Note Added: 0009459
2017-06-25 09:36 abdullah Status closed => feedback
2017-06-25 09:36 abdullah Resolution fixed => reopened
2017-06-25 09:36 abdullah Note Added: 0009522
2017-06-25 09:36 abdullah Note Edited: 0009522
2017-11-20 10:08 DeepSOIC Note Added: 0010435
2017-11-20 10:10 DeepSOIC Note Edited: 0010435
2018-01-02 17:51 abdullah Target Version 0.17 => 0.18
2018-01-02 17:56 abdullah Note Added: 0010674
2019-02-23 20:30 wmayer Target Version 0.18 => 0.19
2019-04-06 19:15 Kunda1 Assigned To abdullah =>
2019-04-06 19:15 Kunda1 Status feedback => assigned
2019-04-06 19:15 Kunda1 Note Added: 0013009
2021-02-06 06:43 abdullah Target Version => 0.20