[QUAR] Re: Expressing position in RDF
mjg at cacr.caltech.edu
Tue Oct 14 13:41:28 PDT 2008
On Oct 14, 2008, at 1:17 PM, Rob Seaman wrote:
> Matthew Graham wrote:
>> I'm happy for the philosophical discussion but am also trying to
>> figure out how to actually do something empirical.
> Empiricism is a branch of philosophy, of course :-)
>> I can see exactly the same arguments that we had about using STC in
>> VOEvent applying to representing positions in RDF. The 90:10 rule
>> should apply and whilst it is wonderful that I can describe any
>> position in any coordinate system using ontology X, why can't we
>> have ontology Y that is small and simple (that word again):
>> :myStar stc:UTC-TOPO-FK5#RA 134.56
> This is an opportunity, not a bump in the road. First, start on p.
> 179 of the ADASS XVII proceedings with Pat Wallace's contribution.
> Use ICRS, not FK5.
The identifying string from the STC in the VOEvent packet is UTC-FK5-
> Second, what is your use case? It appears to be the expression of
> coordinates of an unresolved object fixed to the celestial sphere.
> You are seem to be implicitly in a regime in which proper motion can
> be ignored. Perhaps this should be made explicit in some fashion.
> Note that "unresolved", "fixed", and "no proper motion" are
> orthogonal to the STC issues.
> One STC issue you must address (implicitly or explicitly) is
> parallax. Is the "star" far enough away that this is negligible for
> your purpose(s)? Another STC issue is whether you are you
> describing spectral observations - i.e., is a doppler correction
> (for the motion of the observer) needed? Depending on the science
> to be pursued, other coordinate issues will arise.
> Third, what is the goal of your application? Are you describing
> coordinates in support of follow-up observations? Or are the
> coordinates themselves somehow pertinent to scientific inferences?
> In the former case, these are targeting coordinates as with
> VOEvent. In the latter case, perhaps you don't want equatorial
> coordinates at all, but rather some galactic coordinate system.
> In short, the celestial coordinates are not inherent to the stars
> themselves. There are other such quantities, some pertaining to the
> point of view, some to the intervening environment. My
> recommendation would be the same for representing these:
> X is a star
> X has environment Y
> Y has reddening Z
> X has reddening Z
My goal is to represent the RA, Dec information contained in the
VOEvent packet in RDFa.
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.
More information about the semantics