Error in Modelica.Mechanics.MultiBody.Frames.Quaternions.Orientation.equalityConstraint

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Reported by hansolsson on 3 Nov 2015 10:43 UTC
Modelica.Mechanics.MultiBody.Frames.Quaternions.Orientation.equalityConstraint seems to allow invalid ("mirrored") solutions.

E.g.:

Modelica.Mechanics.MultiBody.Frames.Quaternions.Orientation.equalityConstraint({1,0,0,0}, {-1,0,0,0});
# {0.0, 0.0, 0.0}
Modelica.Mechanics.MultiBody.Frames.Quaternions.orientationConstraint({1,0,0,0});
# {0.0}
Modelica.Mechanics.MultiBody.Frames.Quaternions.orientationConstraint({-1,0,0,0});
# {0.0}

They are generated from planarRotation({+/-1,0,0}, pi);

One solution would be (similarly to rotation matrices) to use atan2(..., Q1*Q2).

The "obvious" solution:

residue := [Q1[4], Q1[3], -Q1[2], -Q1[1]; -Q1[3], Q1[4], Q1[1], Q1[1], Q1[2], Q1[3], Q1[4]]*Q2-{0,0,1}

(assuming it has a unique solution) leads to an illconditioned Jacobian in combination with the orientationConstraint.

This is not good at all, but the quaternion class is not used in the connectors, which explains the low priority and high severity

I believe I earlier reported a similar issue in
Modelica.Mechanics.MultiBody.Frames.Orientation.equalityConstraint
which has now been corrected, but couldn't find the ticket-number.

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Migrated-From: https://trac.modelica.org/Modelica/ticket/1817

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Comment by beutlich on 3 Nov 2015 13:47 UTC
Replying to [ticket:1817 hansolsson]:

I believe I earlier reported a similar issue in
Modelica.Mechanics.MultiBody.Frames.Orientation.equalityConstraint
which has now been corrected, but couldn't find the ticket-number.

#313 perhaps?

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Comment by hansolsson on 3 Nov 2015 14:24 UTC
Replying to [comment:1 beutlich]:

Replying to [ticket:1817 hansolsson]:

I believe I earlier reported a similar issue in
Modelica.Mechanics.MultiBody.Frames.Orientation.equalityConstraint
which has now been corrected, but couldn't find the ticket-number.
#313 perhaps?

No, and it turns out that it wasn't reported on trac.modelica.org for the obvious reason that the error was from 2007-07-03 which predates trac.modelica.org by a few months.

It was still committed to svn.modelica.org.

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Comment by otter on 12 Jan 2016 16:13 UTC
Fixed in ca2852e as suggested

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Changelog modified by otter on 12 Jan 2016 16:13 UTC
Quaternions equality constraints formulation improved to avoid wrong "mirror" solution