Possible Bug. Sketcher issue when applying tangent to two arcs

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Karl1459
Posts: 9
Joined: Sat Nov 04, 2017 8:41 pm

Possible Bug. Sketcher issue when applying tangent to two arcs

Post by Karl1459 » Sat Dec 21, 2019 8:14 pm

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.4 (GitTag)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 980bf9060e28555fecd9e3462f68ca74007b70f8
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)

New Drawing.
In Part design create new body, then new sketch.
In sketcher,
Making two arcs with one point on each arc coincident to each other.
Then attempting to apply the tangent constraint.
Coincident constraint is BROKEN. Tangent is not applied.

Workaround.
Apply tangent constraint First.
Make arcs points coincident Second.
Attachments
SketcherBug1.FCStd
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SketcherBug2.FCStd
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SketcherBug3.FCStd
(4.97 KiB) Downloaded 4 times
SketcherBugStep1.jpg
SketcherBugStep1.jpg (107.33 KiB) Viewed 246 times
SketcherBugStep2.jpg
SketcherBugStep2.jpg (108.71 KiB) Viewed 246 times
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DeepSOIC
Posts: 7292
Joined: Fri Aug 29, 2014 12:45 am
Location: Saint-Petersburg, Russia

Re: Possible Bug. Sketcher issue when applying tangent to two arcs

Post by DeepSOIC » Sat Dec 21, 2019 8:31 pm

Karl1459 wrote:
Sat Dec 21, 2019 8:14 pm
Apply tangent constraint First.
Make arcs points coincident Second.
This is incorrect (well, it may not be from user's standpoint, but let's say it's a problem with how the solver works, fundamentally). You should select endpoints of the two arcs (before they are coincident), and apply tangent. This will make a tangent connection, with well-defined constraint math.

Sketcher attempted to fix your mistake, but it's been reported already that it doesn't work when auto-remove-redundants is enabled. That is indeed a bug.
Karl1459
Posts: 9
Joined: Sat Nov 04, 2017 8:41 pm

Re: Possible Bug. Sketcher issue when applying tangent to two arcs PREVIOUSLY REORTED

Post by Karl1459 » Sun Dec 22, 2019 8:16 am

Thanks for the quick evaluation and reply. Your time is appreciated!
I attempted the exercise with the "auto remove redundancies" box unchecked, and (from my users perspective) received the expected result. So that IS the issue.
Perhaps in the future, for those of us in the great unwashed masses not familiar with constraint math, documentation of the hierarchy of constraint actions would be helpful... maybe version 5.x or so...
chrisb
Posts: 21407
Joined: Tue Mar 17, 2015 9:14 am

Re: Possible Bug. Sketcher issue when applying tangent to two arcs

Post by chrisb » Sun Dec 22, 2019 8:51 am

There is quite some documentation on sketching. You may have a look at https://owncloud.gwdg.de/index.php/s/HS ... I/download
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