Dear UCD list members,
I apologize if the subject of the remarks below has already been addressed or this turns out eventually to be outside the scope of the UCD field. This is both a remark on the UCD electromagnetic spectrum scheme and a question about the use of UCDs.
I have browsed the archive of the UCD mailing list and found only one message, by Patricio Ortiz, already a long time ago (October 2003, http://www.ivoa.net/forum/ucd/0310/0067.htm) that fits this topic and looked quite sound to me.
One of the claimed aims of UCDs is interoperability. Therefore, they should serve, for instance, the purpose of comparing magnitudes from different catalogues in given filters. Therefore, one should be able to identify unambiguously through which filter, photometric system, ... a magnitude is supplied in a catalogue or by a simulation tool.
In the division of the electromagnetic spectrum in the UCD document, optical and near-infrared subparts of the spectrum where given names which are the ones of filters in the Johnson, ... photometric system, whereas they designate contiguous portions of the electromagnetic spectrum.
While Johnson filters do fit in the subparts so defined, this is not
always the case for filters from other photometric systems. For
instance, the g filter of the SDSS photometric system has an effective
wavelength of 482.5 nm but the flux in this band encompasses widely both
the em.opt.B and em.opt.V domains.
On the other hand, there seems to be,as far as I can see, no UCD which
refers to the specification of a photometric system which could
complement the UCD for the description of the electromagnetic spectrum
subpart.
Alternatively, the UCDs for specific filters such as those of SDSS' system, which could become more widespread that Johnson's in the future, could be handed over to particular namespaces. But it then still seems to me that, in order to release ambiguity in the meaning of optical and near-infrared parts of the spectrum, the corresponding UCDs should be named slightly differently, not simply U, B, V, ...
Finally, if the desired achievement of identifications of data columns in the purpose of comparaison is beyond the scope of UCDs, should the cross-comparaison process be handed over to VO tools at more sophisticated levels ?
Thanks in advance for your remarks and comments.
Best regards,
Bernard Debray
Bernard Debray bernard.debray-at-obs-besancon.fr Observatoire de Besançon http://www.obs-besancon.fr/BP 1615
Andrea Preite Martinez wrote:
>Dear member of the UCD_wg,
>
>since last Friday (20050429) an updated list of UCD words is available at:
>
>http://vizier.u-strasbg.fr/UCD/ucd1p-words.txt
>
>at the UCD page:
>
>http://vizier.u-strasbg.fr/UCD/
>
>The new list of words has been edited according to the very valuable
>comments coming from the community and also thanks to the (almost!) every
>day use of them made by Sebastien and myself.
>
>The most important differences with the previous version (20040823) concern
>
>- distances and sizes (linear/angular)
>- the introduction of a rectangular/cartesian reference frame
>- the phot.color section, much simplified
>- spelling, abbreviations, syntax ...
>
>
>At the UCD page you can also find un updated version of the UCD_tree
>browser(s)
>and a new tool, the ucd_builder:
>
>http://vizier.u-strasbg.fr/UCD/cgi-bin/descr2ucd
>
>that uses a description in "natural" language to find the relevant
>ucd_words, and then tries to build a valid ucd out of them.
>
>In these two weeks before Kyoto please explore the list, use the tools and
>send back comments.
>A more "formal" comment page is available to suggest changes in the list of
>words at:
>http://vizier.u-strasbg.fr/UCD/cgi-bin/comment/ucdComments
>
>Have fun.
>Andrea
>
>
Received on 2005-05-09Z18:42:07