Alberto.Micol at eso.org
Sun Sep 17 02:42:59 PDT 2006
Roy Williams wrote:
> Well then they are not compliant. I just want to know if there is a
> serious momentum to clean up the sexg mess. Am I the only person
> who thinks it's a mess? If so, then I will be happy to forget about
It would be actually useful to have a precise definition which could be
used in VOTABLE context, as part of the standard.
Is this the inauguration of the IVOA Data Type WG? ;-)
On Sep 17, 2006, at 03:09, Tom McGlynn wrote:
> There are lots of perfectly readable coordinates that would flunk
> and are used in the literature.
> I do not believe you want to use a system that simply throws out the
> the non-numeric pieces of the coordinates.
If the non-numeric pieces matter, then IVOA should be strict in defining
a minimal list of possible separators/qualifiers. But I would firmly
that it is not necessary to rely on those,
beacuse in IVOA-speak the units will be known by the "unit" attribute,
not by parsing the coordinate value.
Roy's scheme has the small advantage that parsing a sexg rendered in
(15<sup>d</sup> 48<sup>m</sup> 33<sup>s</sup>) is possible, though
HTML is not IVOA-speak.
> They provide information
> about the fields and also facilitate disambiguation with
> target names.
Regarding target names, I guess that in the VO world
the UCD will always tell us what the field is, and nobody
will use a sexg parser on a target name.
Hence 4C+48.61 is not a problem.
Help: I thought the ucd for the target name was under the obs. tree,
but I cannot find it. What is it?
In the old days was: ID_TARGET, but now? Was it removed?
> has only 4 integer fields and no whitespace, but it's still clear
> which is the RA and Dec
> Other heuristics that could be used....
> If a number is signed and it is not the first field, it must be
> the start
> of the second coordinate.
One way would be to enforce the sign for the second coordinate as a
recognised separator, but please...
> A comma can be used to separate the lat/lon coordinates, but not
> the fields within them.
... please please do not enforce the comma separator!
I really hate it, it is not necessary. Astronomers like to "paste"
the coordinates into a search field, without having to edit it to add
or similar superfluous (I'd say even spurious) characters.
> If the separator after something other than the first field is
> 'd', 'deg', 'degree' or
> the non-ASCII degree character, this preceding field is the first
> field in
> the second coordinate (especially if there is a cooresponding
> after the first field)
> If the total number of fields is >2 and < 6, and the first separator
> is a legal, non-space separator (e.g., ':') and the second separator
> is white-space, then the second coordinate begins in the
> third field.
Yap, but that is quite complex...
> Might also consider values
> 13 24 81 47
> is not ambiguous
In general xx xx xx xx is ambiguous;
13 24 81 47 specifically is not ambiguous because 81 > 60:
Vizier interprets "13 24 81 47" as 13:24:00, 81:47:00
but interprets "20 18 38 02" as 20:18:38, 02:00:00 !!!
A nice Sunday to everybody,
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