[Fixed] Bug on inverted Placement

[dpoen]

Hi everyone !

I've been blaying with the python API, and especiallly the "Placement" object.
I might have found a bug :

In a console :
>>> p = FreeCAD.Placement()
>>> p.Rotation.Angle = 1.57
>>> p.inverse().Rotation.Angle
0.0

That should not be that, ins't it ? I should get -1.57, right ?

Thanks !

OS: Debian GNU/Linux 11 (bullseye) (XFCE/xfce)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Python version: 3.9.2
Qt version: 5.15.2
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/United States (en_US)

[openBrain]

Hello,

What you do have basically no sense. A rotation is defined by not only an angle, but also an axis.
If we don't have the axis (especially for first, but let's say for both), it's just 2 numbers.

[dpoen]

Yes, and the axis is by default (0,0,1), so the inverted rotation should either be the same angle (1.57) but with the opposite axis (0,0,-1), or use the same axis (0,0,1) but using the opposite angle (-1.57)

Both way, the rotation angle should not be 0, imo

EDIT : I just look up, and it actually choose to invert the axis, so as a follow-up to my example in my first post, if I do :
>>> p.inverse().Rotation.Axis
(0,0,-1)
That should force to display p.inverse().Rotation.Angle = 1.57

I don't agree (or I don't understand you) about "not making sense", and if it actually not make sense, I think the "inverse()" method should be removed from the Placement object.

And additionnaly, this command seems to otherwise work, considering that :
>>> p.inverse().Rotation.Matrix - p.Rotation.Matrix.inverse()
give the zero matrix

Hope I've got your point, and made mine clearer

[marioalexis]

there is a bug in Rotation::inverse(). Only the array representing the quaternion and the Vector3D axis are changed, but not the _angle member.

[marioalexis]

https://github.com/FreeCAD/FreeCAD/pull/7044

[dpoen]

https://github.com/FreeCAD/FreeCAD/pull/7044

Thanks you sir !

[onekk]

Probably this forum discussion will make some light on the matter, that is not trivial and not unique:

Angles discussion about the 24 types of Cardan angles and similar

https://forum.freecadweb.org/viewtopic. ... 5&start=20

You will see also some hints on the math behind the things, in the comment present in the source:

https://github.com/FreeCAD/FreeCAD/blob ... tation.cpp

Hope it helps.

Carlo D.

[onekk]

https://github.com/FreeCAD/FreeCAD/pull/7044

Thanks you sir !

It seems that has been integrated in new builds.

https://github.com/FreeCAD/FreeCAD/comm ... 989800b334