Transf WD Euler transformation

[Laurent MICHEL]

OK, I'm not an expert at all.


Le 03/04/2020 à 17:46, CresitelloDittmar, Mark a écrit :
> Hopefully, the gWCS folks can respond to this more fully.
> It was added in support of their implementation, which I mapped to 
> EulerAngleRotation.  However, looking at that spec 
> <https://docs.astropy.org/en/stable/api/astropy.modeling.rotations.EulerAngleRotation.html>, 
> it appears to support only 3 rotations.
> 
> Mark
> 
> On Fri, Apr 3, 2020 at 9:11 AM Laurent MICHEL 
> <laurent.michel at astro.unistra.fr 
> <mailto:laurent.michel at astro.unistra.fr>> wrote:
> 
>     Hello,
> 
>     I do not practice Euler transformations daily, but according to my
>     college souvenirs, that is by definition a 3D rotation with a well
>     defined sequence of rotation axis.
>     In my understanding, the Euler rotation is even not a particular
>     case of
>     the Transf rotation since the 3 Euler rotations are not about native
>     axis as stated in the definition you give.
> 
>      > Defines a rotation operation in a 3-dimensional cartesian
>     coordinate space, defined as a series of rotations about the native
>     axes (x,y,z)
> 
>     If I'm right, the class should be renamed (RotationSequence ?). If not,
>     my comment is no longer relevant.
> 
>     Laurent
> 
>     Le 02/04/2020 à 16:40, CresitelloDittmar, Mark a écrit :
>      > Laurent,
>      >
>      > This came directly from the implementation group discussions back
>     in Dec
>      > 2018.
>      > gWCS has use cases where more than 3 rotations are useful, for
>     example
>      > EulerRotation(angles=[12, 1, 2, 3], axes=‘xyzx’).
>      > So we've taken this approach of having a sequence of EulerAngles
>     which
>      > specify the 'axis of rotation' (of the 3D space as either 'x',
>     'y', or
>      > 'z') and angle.
>      >
>      > Mark
>      >
>      >
>      > On Thu, Apr 2, 2020 at 8:31 AM Laurent MICHEL
>      > <laurent.michel at astro.unistra.fr
>     <mailto:laurent.michel at astro.unistra.fr>
>      > <mailto:laurent.michel at astro.unistra.fr
>     <mailto:laurent.michel at astro.unistra.fr>>> wrote:
>      >
>      >     Dear,
>      >
>      >     My comment #1: Why is the Euler Transformation class so complex?
>      >
>      >     - It is always a 3D transformation, this there is no reason
>     to setup a
>      >     1-* aggregation with angles.
>      >
>      >     - Euler angles (nutation, rotation, intrinsic rotation) are well
>      >     defined, there is no need for a specific datatype
>     (EulerAngle). So we
>      >     could just have 3 class attributes.
>      >
>      >     - Using a specific datatype where angles are identified by a the
>      >     name of
>      >     the rotation axis supposes we have a vocabulary for this,
>     which is a
>      >     bit
>      >     complicated for this purpose with the risk a implementation
>     errors.
>      >
>      >     Take care of yourself.
>      >
>      >     LM
>      >
>      >     --
>      >     ---- Laurent MICHEL              Tel  (33 0) 3 68 85 24 37
>      >            Observatoire de Strasbourg  Fax  (33 0) 3 68 85 24 32
>      >            11 Rue de l'Universite      Mail
>      > laurent.michel at astro.unistra.fr
>     <mailto:laurent.michel at astro.unistra.fr>
>     <mailto:laurent.michel at astro.unistra.fr
>     <mailto:laurent.michel at astro.unistra.fr>>
>      >            67000 Strasbourg (France)   Web
>     http://astro.u-strasbg.fr/~michel
>      >     ---
>      >
> 
>     -- 
>     ---- Laurent MICHEL              Tel  (33 0) 3 68 85 24 37
>            Observatoire de Strasbourg  Fax  (33 0) 3 68 85 24 32
>            11 Rue de l'Universite      Mail
>     laurent.michel at astro.unistra.fr <mailto:laurent.michel at astro.unistra.fr>
>            67000 Strasbourg (France)   Web http://astro.u-strasbg.fr/~michel
>     ---
> 

-- 
---- Laurent MICHEL              Tel  (33 0) 3 68 85 24 37
      Observatoire de Strasbourg  Fax  (33 0) 3 68 85 24 32
      11 Rue de l'Universite      Mail laurent.michel at astro.unistra.fr
      67000 Strasbourg (France)   Web  http://astro.u-strasbg.fr/~michel
---