content, format, ctype, or xtype ?

[Francois Ochsenbein]

Hi Arnold,

I imagined the STC-library would solve that ?

Seriously speaking, there are many ways of accomodating a search
in a system different from the one stored in the columns of the
data-base -- the most stupid one being to compute on the fly
the missing coordinates (in your example which represents 25% of
the sky) or using healpix, htm or any other sky sectioning which
patches your region.

If it could already be possible to agree on one common system
(preferably the most accurately defined one) before requiring
that all data servers are storing and delivering their data in
several systems, it would be already a large step toward interoperability !
In the vast majority of applications, a common system is enough:
cross-matching, and searches in circular regions don't require a
specific system, just knowing which one is the standard system,
and expressing our coordinates in that system does the job.

Cheers, Francois

>
>Francois,
>
>Here is the issue:
>If a user queries a catalog for, say 90 < l <270 AND -30 < b < 30
>you have to do an on-the-fly transformation of almost all your RA,Dec
>entries in order to make sure you get the right subset.
>
>With storage getting cheaper and cheaper it is far more cost-effective
>to take the hit there and be able to perform the queries very efficiently.
>
>The only ones you need are (FK4 or FK5 or ICRS) and Galactic and Ecliptic.
>
>  - Arnold
>
>Francois Ochsenbein wrote:
>>
>> Hi Alberto,
>>
>> Just a precision about vizier (at the end of your message):
>> while coordinates in 'standard' frames are computed on the
>> fly, they are not actually stored (currently) in vizier.
>> I'm not a fan of adding gigabytes of computed data to gigabytes
>> of original data; and as far as celestial positions are concerned,
>> I would better promote a standardisation to a common reference frame
>> rather than asking every data provider to understand, compute
>> and eventually store positions in galactic, ecliptic, icrf, fk4,
>> etc etc...
>>
>> --Francois
>>

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Francois Ochsenbein    ------   Observatoire Astronomique de Strasbourg
   11, rue de l'Universite 67000 STRASBOURG  Phone: +33-(0)390 24 24 29
Email: francois at astro.u-strasbg.fr (France)    Fax: +33-(0)390 24 24 17
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