Relationship between Q and STC

[David Berry]

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). 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.

> 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

----------------------------------------------------------------------
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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