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<p>Dear Apps members,</p>
<p>This is an announcement of <b>the </b><b>Erratum 1 concerning
VOTable 1.3</b>, which has been accepted by the IVOA TCG during
the last Interop Meeting at Shanghai.</p>
<p>Consequently of this erratum, we encourage any VOTable providers
to re-introduce as soon as possible the coordinate system
description thanks to the COOSYS mecanism for avoiding bad VO tool
assumptions for coordinates provided in other epoch than J2000
(notably the case for Gaia DR1: J2015 epoch) - see details below.<br>
</p>
<p>Best regards<br>
Pierre Fernique</p>
<p>--</p>
<h2>VOTable-1.3 Erratum 1 - COOSYS un-deprecation </h2>
<p>
Author: Pierre Fernique - Application Working Group Chair<br>
Date: 31 March 2017<br>
Accepted by TCG: 14 May 2017
</p>
<p>
The following set of Errata amends the VOTable-1.3 (Ochsenbein et
al. 2013) recommendation.
</p>
<h3>Rationale </h3>
<p>
The 1.3 VOTable document has introduced several references to the
IVOA note "<em>Referencing <a
href="http://wiki.ivoa.net/twiki/bin/view/IVOA/STC"
class="twikiLink">STC</a> in VOTable</em>" version 1.1
(Ochsenbein et al. 2009) and version 2.0 (Demleitner et al. 2010)
for replacing progressively the usage of the basic COOSYS element
used since VOTable 1.0. and dedicated to describe coordinate
systems.<br>
<br>
Due to their status, these notes have not been endorsed by the
IVOA. And as any IVOA note, they are just expressing suggestions
from and opinions of the authors, and are not a recommendation.
Additionally, these two versions of the same note describe
different and not compatible methods. This fact introduces
inconsistencies: the example provided in the VOTable 1.3 document
has been retrieved from the version 2.0 of this note. The
bibliographic reference at the end of the document points to the
note version 1.1.<br>
<br>
Consequently, most of generated VOTables continue to use COOSYS,
or worst, just remove the COOSYS element but without replacing it
by the solution described in the note 1.1 or alternatively note
2.0. In absence of coordinate system description, VO clients may
assume that the default coordinate system is FK5 or ICRS, epoch
J2000, and it is generally the case. The first release of the Gaia
mission - in 2016 - based on ICRS coordinates in epoch J2015
breaks this assumption.
</p>
<p>
<br>
This problem has been exposed and demonstrated at the IVOA Interop
meeting at Trieste in 2016 (T.Boch - VO access to Gaia). A
consensus was reached for writing this errata document, in order
to remove the references to these IVOA notes, and to undeprecate
and encourage the usage of COOSYS until the next version of the
VOTable standard is released. <br>
</p>
<h3>Impact Assesment </h3>
<p>
The changes described by this erratum should impact only the 2
services which are using note 1.1 description (IMCCE) and note 2.0
description (GAVO) (see P.Fernique presentation "<em>Coordinate
issue</em>"). Both agreed to re-introduce COOSYS definitions.
The IVOA services which had totally removed coordinate system
description are encouraged to re-introduce it based on COOSYS. <br>
</p>
<p>--<br>
</p>
<p>The whole Errata document is available at this address:
<a class="moz-txt-link-freetext" href="http://wiki.ivoa.net/twiki/bin/view/IVOA/VOTable-1_3-Err-1">http://wiki.ivoa.net/twiki/bin/view/IVOA/VOTable-1_3-Err-1</a></p>
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