Point in Coord

[Laurent MICHEL]

Mark


I do not propose to turn back toward Frame-centric coords 
(GalacticPosition...)
I'm just proposing to add a new class without altering the model structure.
This class would be specific to the celestian sphere (lon/lat) and 
should be attached to a frame (ICRS...) as any other Point.

It would be nice to get feebacks from other people on this.

LM

Le 08/04/2020 à 23:30, CresitelloDittmar, Mark a écrit :
> Laurent,
> 
> The hierarchy is: Point references a SpaceSys which contains the 
> SpaceFrame and the CoordSpace (both in composition).
> Point
>     |-> SpaceSys
>           o-> SpaceFrame
>           o-> PhysicalCoordSpace{Cartesian/SphericalCoordSpace}
> 
> But that does not negate the question.
>    "However, taking into consideration that spatial coordinates is the 
> most used thing in Astronomy, I'm wondering if it wouldn't be better to 
> have one specific class for Cartesian points (refering to 
> CartesianCoordSpace) and another for Spherical points (refering to 
> SphericalCoordSpace)."
> 
>    * Earlier drafts of Coords (2018) had Frame-centric coords with 
> standard spaces (CartesianCoord, LongLatCoord)..
>    * Due to feedback on this representation, they migrated in 2019 to 
> specialized singular coordinates (X,Y,Z,Long,Lat,R, etc) which referred 
> to axes of standard spaces, and were used in frame-centric Measures.  
> Which is what went to the RFC phase.
>    * There, the frame-centric and space-centric Measures were generally 
> disliked (GalacticPosition, CartesianPosition)
>    * The RFC actions called for replacing the specialized singular 
> coordinates with a single Point Coordinate, and removing the specialized 
> Measures, retaining only the single Position type containing a Point.  
> The consequence of users having to interrogate the Position to determine 
> the details of frame/space was considered acceptable.
> 
> Obviously there is a sweet spot there somewhere, but I doubt we can 
> settle into it until we have more implementation experience with it.  
> Adding a CartesianPoint and SphericalPoint which constrains the space is 
> a simple update which can be done at any time.
> 
> Mark
> 
> 
> 
> 
> 
> On Tue, Apr 7, 2020 at 5:42 AM Laurent MICHEL 
> <laurent.michel at astro.unistra.fr 
> <mailto:laurent.michel at astro.unistra.fr>> wrote:
> 
>     Dear DM
> 
>     I'm exercising with Coords with spatial coordinates.
> 
>     My understanding is as follow:
>     ==============================
>     Spatial coordinates are represented by Point instances that, skipping
>     the details, refers to a SpaceSys that refer to a SpaceFrame that refer
>     to a PhysicalCoordSpace that is either a SphericalCoordSpace or a
>     CartesianCoordSpace.
> 
>     Point
>         |-> SpaceSys
>               |-> SpaceFrame
>                    |-> PhysicalCoordSpace{Cartesian/SphericalCoordSpace}
> 
>     So a client that gets a Point instance will have to step down this
>     cascade and to check the class of the associated PhysicalCoordSpace
>     instance before to know whether this point is  Cartesian or Spherical.
> 
>     Question:
>     ========
>     This is consistent but not very practical. I understand that this model
>     provides components for host models that will be designed in a way to
>     avoid clients to do such inferences. This could be the case with the
>     upgrade of Meas.
>     However, taking into consideration that spatial coordinates is the most
>     used thing in Astronomy, I'm wondering if it wouldn't be better to have
>     one specific class for Cartesian points (refering to
>     CartesianCoordSpace) and another for Spherical points (refering to
>     SphericalCoordSpace).
> 
>     As a side effect this would allow to have one specific spherical
>     CoordSpace for the celestial sphere (lat ,long, R=1).
> 
>     Laurent
>     -- 
>     ---- 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
---