Relationship between Q and STC

[Brian Thomas]

On Monday 10 May 2004 01:56 pm, David Berry wrote:
> Brian,
>
> > > An STC document is exactly equivalent to a Frame, and could be seen as
> > > a serialisation of a Frame. There is one complication though -  in
> > > addition to defining a coordinate system, an STC document can also
> > > specify a particular region within that coordinate system. Currently
> > > the Q document does not have a model for a Region. But it could have -
> > > I'm adding one to the AST library as we speak (when and as I get time
> > > off from other things).
> >
> > 	David,
> >
> > I sort of agree, but STC (I think) oversteps into domain of Q for
> > specification of coordinates, and the Q does it better;
>
> Oooh. Not sure about that! STC is just *directly* equivalent to a Frame
> (excepting the Region issue). 

	What about the axes information? Why not re-use the Q for this?

> Admitedly it is only one class of Frame -
> there will be many others classes of Frame (FluxFrame, TemperatureFrame,
> etc), but never-the-less STC is complete and corresponds precisely to what
> I understand as a Frame (excepting Regions).
>
> > This part should be in the Q. Furthermore,
> > the ST part of "STC" can be realized as a quantity.
>
> But a Quantity should be "a rule for obtaining values", and STC
> specifically excludes issues to do with obtaining values - its just
> defines the coordinate syetem and so is a Frame, not a Q.

	Thats not true. I see components of the STC as quantities, 	
	for example "StandardReferencePosition" is a quantity, albeit one
	which is allowed to  take one of a restricted set of values, e.g. 
	"GEOGENTER", "BARYCENTER", etc.

	And if I can get all the component parts of the ST to be Q's (and
	I can) then this means at the STC itself can be a Q (as StandardQ
	allows holding "member" Q's).

	Technically (and I think philosophically) tt works out quite well for 
	every part of the STC and is a great demonstration of how the Q 
	can be used by the VO. See the proposal.

>
> > Finally, I think that "Region" should be a separate namespace and not in
> > the Q. I think thats how the stc_test stuff I posted has done it..
>
> Yes, how to integrate Regions into this takes a bit more thought.
>
> David

	=bt.

>
> ----------------------------------------------------------------------
> Dr David S. Berry    (dsb at ast.man.ac.uk)
>
> STARLINK project		 |	Centre for Astrophysics
> (http://www.starlink.ac.uk/)	 |	University of Central Lancashire
> Rutherford Appleton Laboratory	 |	PRESTON
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-- 

  * Dr. Brian Thomas 

  * Dept of Astronomy/University of Maryland-College Park 
  * Code 630.1/Goddard Space Flight Center-NASA

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