0003976: Solver falsely detects redundant constraints in specific conditions - FreeCAD Tracker

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ID	Project	Category	View Status	Date Submitted	Last Update

0003976	GCS	Bug	public	2019-05-15 20:13	2021-02-06 06:31

Reporter	openBrain	Assigned To
Priority	normal	Severity	major	Reproducibility	always
Status	confirmed	Resolution	open
Product Version	0.18
Target Version	0.20

Summary	0003976: Solver falsely detects redundant constraints in specific conditions
Description	In some specific conditions, solver falsely detects redundant constraints. It happens when 2 lines/curves are tangent by design but not by constraint.
Steps To Reproduce	With minimal attached file : Remove 2.5 mm constraint and try to add a radius constraint to the arc => The solver falsely detects a redundant constraint Reset sketch to initial state, change 4 mm constraint to 3 mm then repeat same as previous step => The solver correctly find a fully constrained sketch
Additional Information	Forum thread --- Other example file that produces the same issue by chrisb --- OS: Ubuntu 18.04.2 LTS Word size of OS: 64-bit Word size of FreeCAD: 64-bit Version: 0.18.1. Build type: Release Python version: 2.7.15rc1 Qt version: 5.9.5 Coin version: 4.0.0a OCC version: 7.3.0 Locale: French/France (fr_FR)
Tags	No tags attached.

FreeCAD Information

openBrain 2019-05-15 20:13 developer	solver_redundant_bug.FCStd (3,694 bytes)

DeepSOIC 2020-03-29 20:05 developer ~0014313	This is the same kind of problem as with coincident+tangent combo. You have enforced top line tangent to arc by means of other constraints. The point connecting the circle and the line must be computed by finding an intersection between the two, which is an ill-posed problem for the solver when they are tangent. The false detection of redundancy comes from vanishing of jacobi matrix row when the sketch is precisely solved. This is also exactly what a redundancy looks like. If the solution is slightly inaccurate (e.g. if you move the point away a bit before applying radius constraint), there won't be a false redundancy message. I'm afraid this is unfixable. Having at least some warning (i.e. a false redundancy warning) may be better than nothing, actually.

openBrain 2020-03-29 21:53 developer ~0014314	@DeepSOIC : I'm not sure this is exactly same case as coincident+tangent. In the reproducing procedure, a DOF is released by removing the "2.5 mm" length. This is super weird as if you follow the procedure and try to validate an arc radius (any value), it will refuse it with "sketch contains conflicting constraints". Just change the 2.5 mm length to any other before removing it, and then any value of arc radius is correctly accepted (leading to fully constrained sketch). Even a 2.5 mm radius is correct.

yorik 2022-03-03 13:55 administrator ~0016765	This ticket has been migrated to GitHub as issue 5931.

Date Modified	Username	Field	Change
2019-05-15 20:13	openBrain	New Issue
2019-05-15 20:13	openBrain	File Added: solver_redundant_bug.FCStd
2019-06-17 06:48	Kunda1	Status	new => confirmed
2019-06-17 06:48	Kunda1	Target Version	=> 0.19
2020-03-29 20:05	DeepSOIC	Note Added: 0014313
2020-03-29 21:53	openBrain	Note Added: 0014314
2020-11-10 12:56	abdullah	Target Version	0.19 => 0.20
2021-02-06 06:31	abdullah	Target Version	=> 0.20