On Mon, 24 Apr 2006, Thomas McGlynn wrote:
> Hi Doug,
>
> I certainly thought that is what we intended but
> I don't think that's what the document says.
>
> The SIA document is quite clear that all inputs are
> in decimal degrees. However it doesn't say a thing
> about outputs. All it does is to specify that
> the type of the column with the POS_EQ_RA/DEC_MAIN
> UCDs shall be of type double. I believed this meant
> that the type was a scalar, but the discussion that
> have come up on sexagesimal coordinates and in particular
> the USNO Cone search services, indicates that others
> don't in practice agree even with that.
For the record, I agree that a common-sense reading of the existing text strongly suggests a scalar double column for output. In my earlier comment:
On Fri, 21 Apr 2006, Mark Taylor wrote:
> On Thu, 20 Apr 2006, Thomas McGlynn wrote:
> >
> > > At it's clear that the USNO table is incorrect in the new version
> > > (since it specifies that the column is a double).
> >
> > I've just retrieved a table from the USNO-B conesearch using the URL:
> > http://www.nofs.navy.mil/cgi-bin/vo_cone.cgi?CAT=USNO-B1&RA=50.1&DEC=-37.5&SR=0.16
> > It has RA and DEC FIELD components with the attributes
> >
> > datatype="double" arraysize="3x1"
> >
> > which, while you might argue it's eccentric, is not incorrect, this is
> > exactly how you specify an array-valued column according to both
> > versions 1.0 and 1.1 of the standard.
what I meant was that the column was legal as far as the VOTable standard goes, I wasn't thinking about the SIAP specification document.
However:
> I don't think there is any support in the standard
> for the statement that the units of the coordinate centers are degrees.
> Only the units of the Image_Scales are specified (of the required fields).
>
> The language for the coordinate columns in the Cone search is almost the
> same as for the SIA.
>
> Cone search spec:
> Exactly one FIELD must have ucd="POS_EQ_RA_MAIN", with type double,
> representing the J2000 right-ascension of the source.
>
> SIA Spec:
> Exactly one field MUST have ucd="POS_EQ_RA_MAIN", with datatype="double",
> representing the ICRS right-ascension of the center of the image.
>
> I would suggest that in both standards we need language more like:
>
> The table must contain one and only one field with the UCD "POS_EQ_RA_MAIN". This field
> must be a scalar, with no arraysize specified, and with datatype="double" and unit="degrees".
> The value of this field shall be the ICRS right ascension of the center of the
> image expressed in decimal degrees.
rewording it more rigorously can only be a good thing.
Note however that to comply with the unit specifications mandated in the VOTable document (http://vizier.u-strasbg.fr/doc/catstd-3.2.htx) it ought to be units="deg", not "degrees".
Mark
-- Mark Taylor Astronomical Programmer Physics, Bristol University, UK m.b.taylor@bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/Received on 2006-04-24Z19:16:32