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0023400Community[OCCT] OCCT:Meshpublic2012-08-24 11:482014-11-11 13:01
Fabian Hachenberg 
normaljust a question 
[OCCT] 6.5.3 
[OCCT] 6.8.0[OCCT] 6.8.0 
bugs vis(004) bug23400
0023400: Triangulation of thin ring contains gap
Hi, I', wondering whether this behaviour is valid. I triangulate a thin ring using the following meshing parameters
deflection (relative) = 0.5
angular_deflection = 0.6

As you can see in the attached screenshot, a gap appears in the ring. I would have expected that the triangulation is always preserving the topology of the shape?
No tags attached.
related to 0024084assigned oan Open CASCADE Additional tool for resolving 2d loops on discretized wires should be implemented in BRepMesh 
related to 0025063closed bugmaster Open CASCADE Visualization - 2D objects are not displayed at some camera positions 
? thinring.brep (13,778) 2012-08-24 11:48
png thinring.png (11,114) 2012-08-24 11:49
png overlapping.png (3,727) 2013-03-07 17:24
Issue History
2012-08-24 11:48Fabian HachenbergNew Issue
2012-08-24 11:48Fabian HachenbergAssigned To => jgv
2012-08-24 11:48Fabian HachenbergFile Added: thinring.brep
2012-08-24 11:49Fabian HachenbergFile Added: thinring.png
2012-11-09 10:51abvCategoryOCCT:Modeling Algorithms => OCCT:Mesh
2013-03-07 17:24oanNote Added: 0023629
2013-03-07 17:24oanFile Added: overlapping.png
2013-03-07 17:24oanAssigned Tojgv => Fabian Hachenberg
2013-03-07 17:25oanStatusnew => feedback
2013-07-23 12:25oanRelationship addedrelated to 0024084
2014-07-09 12:49oanNote Added: 0030024
2014-07-09 12:49oanAssigned ToFabian Hachenberg => kgv
2014-07-09 13:42kgvRelationship addedrelated to 0025063
2014-07-09 13:57kgvNote Added: 0030027
2014-07-09 13:57kgvAssigned Tokgv => oan
2014-07-09 15:41kgvNote Edited: 0030027bug_revision_view_page.php?bugnote_id=30027#r7691
2014-09-12 10:04abvTarget Version => 6.8.0
2014-09-26 06:16abvNote Added: 0032179
2014-09-26 16:03oanAssigned Tooan => bugmaster
2014-09-26 16:03oanNote Added: 0032250
2014-09-26 16:03oanStatusfeedback => assigned
2014-09-26 16:04oanNote Edited: 0032250bug_revision_view_page.php?bugnote_id=32250#r8149
2014-09-26 16:24abvStatusassigned => feedback
2014-09-29 15:42bugmasterAssigned Tobugmaster => mkv
2014-10-08 20:32gitNote Added: 0032847
2014-10-08 20:46mkvNote Added: 0032851
2014-10-08 20:46mkvAssigned Tomkv => bugmaster
2014-10-08 20:46mkvStatusfeedback => tested
2014-10-08 20:46mkvTest case number => bugs vis(004) bug23400
2014-10-13 17:52bugmasterChangeset attached => occt master e2fd181c
2014-10-13 17:52bugmasterStatustested => verified
2014-10-13 17:52bugmasterResolutionopen => fixed
2014-10-21 16:42gitNote Added: 0033419
2014-11-11 12:43aivFixed in Version => 6.8.0
2014-11-11 13:01aivStatusverified => closed

2013-03-07 17:24   
Problem is not reproduced on OCC build based on the current master, ring appears without any gaps.

From the other side I suppose this case is caused by overlapping between the discretized representations of the inner and the outer circles forming the ring (please see the attached screenshot). In this situation when the square of an appeared loop is too small and the distances between the intersection points and a sampling point are within the deflection this loop may be replaced by a single link shown as a gap.

As a possible solution the angular deflection should be decreased to provide more precise sampling of the circles and avoid intersections.
2014-07-09 12:49   
Dear KGV,

I have faced a problem during visualization of the attached shape. Could you please investigate?

Steps to reproduce:
pload ALL
restore thinring.brep a
vsetdispmode 1
vdisplay a

# An exception was caught 00816588 : Standard_NumericError: FLT MULTIPLE TRAPS
#(possible overflow in conversion of double to integer)
# ** Exception ** 00816588 : Standard_NumericError: FLT MULTIPLE TRAPS
# (possible overflow in conversion of double to integer)
2014-07-09 13:57   
(edited on: 2014-07-09 15:41)
Dear Oleg,

>> I have faced a problem during visualization of the attached shape.
dedicated issue 0025063 has been registered for this regression (since it is irrelevant to this bug description).

Please do not set top view (vtop) as temporary workaround.

2014-09-26 06:16   
Oleg, could you please re-check the actual status of the issue?
2014-09-26 16:03   
(edited on: 2014-09-26 16:04)
Should not appear on current master. Current implementation of BRepMesh_Classifier tries to prevent appearence of such cases.

Moreover, detailed description of the matter is given in first note.

Dear Bugmaster,
please create corresponded test case and check.

2014-10-08 20:32   
Branch CR23400 has been created by mkv.

SHA-1: 022eaa5f1212f3f4bb9731ae992ea86813cf9c0a

Detailed log of new commits:

Author: mkv
Date: Wed Oct 8 20:32:16 2014 +0400

    Test case for issue CR23400
2014-10-08 20:46   
Dear BugMaster,
Test cases bugs/vis(004)/bug23400 is created and pushed to new branch CR23400 of occt git-repository.
Test cases bugs/vis(004)/bug23400 is OK.
2014-10-21 16:42   
Branch CR23400 has been deleted by inv.

SHA-1: 022eaa5f1212f3f4bb9731ae992ea86813cf9c0a