Silly Question about Fully Defined Sketches

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ManiacRS
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Silly Question about Fully Defined Sketches

Post by ManiacRS » Mon Oct 19, 2020 11:07 am

Hello everyone.

I came across this one case where the solver says the sketch is fully defined when geometrically there are other possible solutions. To demonstrate this I deactivated an Equal constraint, moved a line and reactivated the constraint to get a different shape. I will be attaching the pictures below. The correctly fully defined sketch is the one with the 2 angle constraints.

I have come across behaviour like that in other CAD systems too, so I would not classify this as a bug. But I just wanted to know if this can be dealt with by changing the advanced solver options? If not, is this something you guys have come across and have deemed fixable/ worth the effort to fix?

Thx in advance.


OS: Ubuntu 18.04.5 LTS (ubuntu:GNOME/ubuntu)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: 1f0b7793e6e48c18e818f17b082790a4af0124d6
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)
Attachments
Is_it_really-1.png
Is_it_really-1.png (205.79 KiB) Viewed 217 times
Is_it_really-2.png
Is_it_really-2.png (208.72 KiB) Viewed 217 times
This_is_really.png
This_is_really.png (214.62 KiB) Viewed 217 times
jmaustpc
Posts: 10361
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Re: Silly Question about Fully Defined Sketches

Post by jmaustpc » Mon Oct 19, 2020 11:20 am

ManiacRS wrote:
Mon Oct 19, 2020 11:07 am
I came across this one case where the solver says the sketch is fully defined when geometrically there are other possible solutions.
The solver stops at the first closest fully constrained solution, but there are cases where alternative solutions would be available, but the solver stops at the closest solution.
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ManiacRS
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Re: Silly Question about Fully Defined Sketches

Post by ManiacRS » Wed Oct 21, 2020 2:21 pm

OK, I don't know if it's just me running into these issues. Haven't used FreeCAD for too long. But this is definitely a bug.

https://youtu.be/xRABKEnP270

OS: Ubuntu 18.04.5 LTS (ubuntu:GNOME/ubuntu)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: 72eb41b24f12b572d55081042160954b93f4614c
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)
drmacro
Posts: 1933
Joined: Sun Mar 02, 2014 4:35 pm

Re: Silly Question about Fully Defined Sketches

Post by drmacro » Wed Oct 21, 2020 2:36 pm

Could post your FreeCAD file?

I can't duplicate...



OS: Ubuntu 20.04.1 LTS (XFCE/ubuntustudio)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: 72eb41b24f12b572d55081042160954b93f4614c
Python version: 3.8.5
Qt version: 5.12.8
Coin version: 4.0.0
OCC version: 7.3.0
Locale: English/United States (en_US)
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ManiacRS
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Re: Silly Question about Fully Defined Sketches

Post by ManiacRS » Wed Oct 21, 2020 5:27 pm

drmacro wrote:
Wed Oct 21, 2020 2:36 pm
Could post your FreeCAD file?

I can't duplicate...



OS: Ubuntu 20.04.1 LTS (XFCE/ubuntustudio)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: 72eb41b24f12b572d55081042160954b93f4614c
Python version: 3.8.5
Qt version: 5.12.8
Coin version: 4.0.0
OCC version: 7.3.0
Locale: English/United States (en_US)
There you go. Sent two files because I was playing with the Shapebinder between part files to get to know how it works.

Please excuse the slightly rubbish design work up to that point. Was only playing around.
Attachments
Small Stepper.FCStd
(93.59 KiB) Downloaded 4 times
RobotBase.FCStd
(40.04 KiB) Downloaded 4 times
chrisb
Posts: 28855
Joined: Tue Mar 17, 2015 9:14 am

Re: Silly Question about Fully Defined Sketches

Post by chrisb » Thu Oct 22, 2020 12:26 am

I removed some superfluous stuff so that there are no dependencies to an external file.

The culprit in Sketch 002 is Constraint15. It is the coincidence fixing the center of the inner arc to the origin. If it is removed we should see 2 additional DOF; instead we see 3 which is now correct. If I re-apply the coincidence one DOF is left which is correct.

Constraints with circles are sometimes tricky because they tend to consume parts of the DOFs of a constraint, see the bugtracker, there are several such reports among the latest.
Here the number of DOF created by geometry is 34 (6 lines with 24 + 2 arcs with 10) which the same number consumed by the constraints (14 coincidences with 28 + 2 vertical, 3 horizontal, 1 diameter with together 6 DOF)
Abdullah wrote:ping
I guess we have this among the existing tickets with the partially constraints, should we create a ticket anyway?
Attachments
RobotBase_cb.FCStd
(21.35 KiB) Downloaded 1 time
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