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Dear VO App members,<br>
<br>
During the last Interop meeting at Banff, we discussed about the
very bad situation that <b>most of VO members (providers &
clients) are not able to use correctly the coordinate descriptions
recommended in VOTable</b> <b>standard</b>. For people not
present at this meeting, have a look on this PDF : <a
class="moz-txt-link-freetext"
href="http://wiki.ivoa.net/internal/IVOA/InterOpOct2014Applications/AppsWG-VOTable_discusion-Coordinate-issue.pdf">http://wiki.ivoa.net/internal/IVOA/InterOpOct2014Applications/AppsWG-VOTable_discusion-Coordinate-issue.pdf</a><br>
<br>
In one word, since we deprecated COOSYS (2009), <b>only one VO
provider</b> (IMCCE) has been achieved to describe correctly their
coordinates and <b>only one VO client</b> (Aladin) is parsing the
current recommended method ("<i>Referencing STC in VOTable</i>"
note). After 5 years, the worst consequence is certainly the fact
that some providers prefer to remove totally the coordinate
description rather than use the deprecated COOSYS, or try to
implement the STC VOTable note. <br>
Concretely, <b>VO providers and clients assume that coordinates are
probably provided in ICRS/ep2000</b>. Unfortunately, this
assumption will be no longer a solution as some new major missions
will be not provided in epoch J2000 - for instance GAIA epoch J2010.
<b>So the situation is critical</b>.<br>
<br>
<img src="cid:part2.09000103.02080309@astro.unistra.fr" alt=""><br>
<br>
In order to come back to a clean situation, the participants to the
Banff meeting mainly agree to take these two actions:<br>
<b>"Un-deprecate" COOSYS to clean up the situation immediately.</b><b><br>
</b><b>Move to the future VODML STC2 description of coordinates when
it will be ready</b><b> (deprecate the STC note)<br>
</b><br>
The 2 methods (COOSYS, VODML) do not clash, allowing to manage a
smooth transition.<br>
<br>
I contacted directly the unique good student of the class-room
(IMCEE - not present at Banff) and he kindly agreed to adapt his
VOTables according to this solution. In the other side, Aladin will
continue to support the STC note even it will be deprecated.<br>
<br>
But, may be, you were not present at the Banff meeting, and you have
a divergente opinion.<br>
So please, raise your hand and bring your argument (have a look on
your own VOTables before contesting too hardly <span
class="moz-smiley-s3"><span> ;-) </span></span><br>
<br>
In the other hand, if you are generating VOTables without any
coordinate description, please insert as soon as possible the
minimal COOSYS according to your space reference : for instance:
<COOSYS system="ICRS" epoch="J2000" />, see VOTable REC 1.1 -
section 3.3<br>
<h4><i><font color="#4682B4">"The <tt><font color="#8B0000">COOSYS</font></tt>
element</font></i></h4>
<i>
</i><i><a name="elem:COOSYS"></a></i><i>
This element defines a celestial coordinate system, to which the
components of a position on the celestial sphere refer.
It has an </i><i><tt><font color="#8B0000">ID</font></tt></i><i>
attribute -- required if the
</i><i><tt><font color="#8B0000">COOSYS</font></tt></i><i> element
has to be referred to via the </i><i><tt><font color="#8B0000">ref</font></tt></i><i>
attribute
of the position components, which is generally the case --
a </i><i><tt><font color="#8B0000">system</font></tt></i><i>
attribute which specifies the coordinate system
among "</i><i><font color="#8B008B">ICRS</font></i><i>", "</i><i><font
color="#8B008B">eq_FK5</font></i><i>", "</i><i><font
color="#8B008B">eq_FK4</font></i><i>", "</i><i><font
color="#8B008B">ecl_FK4</font></i><i>", "</i><i><font
color="#8B008B">ecl_FK5</font></i><i>", "</i><i><font
color="#8B008B">galactic</font></i><i>", "</i><i><font
color="#8B008B">supergalactic</font></i><i>", "</i><i><font
color="#8B008B">barycentric</font></i><i>", "</i><i><font
color="#8B008B">geo_app</font></i><i>" and a user-defined "</i><i><font
color="#8B008B">xy</font></i><i>" value. </i><i><tt><font
color="#8B0000">equinox</font></tt></i><i> is the parameter
required to fix the equatorial or ecliptic systems (as e.g. "</i><i><font
color="#8B008B">J2000</font></i><i>" as the default "</i><i><font
color="#8B008B">eq_FK5</font></i><i>" or "</i><i><font
color="#8B008B">B1950</font></i><i>" as the default "</i><i><font
color="#8B008B">eq_FK4</font></i><i>"), and </i><i><tt><font
color="#8B0000">epoch</font></tt></i><i> specifies the epoch
of the positions if necessary.
</i><i>"</i><i><br>
</i><br>
<br>
<img src="cid:part4.09000407.02060207@astro.unistra.fr" alt=""><br>
<br>
Best regards<br>
Pierre Fernique<br>
<br>
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