[QUAR] Re: Expressing position in RDF

[Rob Seaman]

I suppose I should mention the aberration of light, too...

On Oct 14, 2008, at 3:15 PM, Rob Seaman wrote:

> Hi Matthew,
>
>> The identifying string from the STC in the VOEvent packet is UTC- 
>> FK5-TOPO.
>
>
> Point taken.
>
>> My goal is to represent the RA, Dec information contained in the  
>> VOEvent packet in RDFa.
>
> Ok.  Assume a simple case.  Note that this cannot be called a  
> "typical" case.  The coordinates for a point-like target fixed on  
> the celestial sphere, with negligible proper motion and parallax.   
> Doppler and light travel corrections are to be dealt with downstream  
> ("TOPO" + metadata for the observatory + epoch).
>
> How does one convey these coordinates (RA, Dec, coordsys,  
> conditionally equinox)?  Well, you either replicate the carefully  
> negotiated truce from STC, or you make additional default  
> specifications.  In either case, the assumptions are implicit in the  
> representation.  One might, for instance, suggest something like:
>
> 	X has a SimpleWCS
> 	SimpleWCS has an RA (and Dec with implicit equinox and coordsys)
>
> My fundamental point is that for proper system engineering you avoid  
> saying:
>
> 	X has an RA
>
> because this locks you into a specific set of assumptions.  Later,  
> perhaps, someone will come up with a SomewhatMoreComplexWCS.  In  
> that case, an application can evolve to support this while retaining  
> backwards compatibility for SimpleWCS.
>
> However it is done, there will be flavors of VOEvent packets that  
> are inappropriate for representation using SimpleWCS.
>
>> I think the answer to my original question is that there is nothing  
>> currently existing in the VO to allow me to do this succinctly.
>
> In that case this represents an opportunity for making an original  
> contribution to the VO and to broader astronomical practice.
>
> Rob
>