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<p>This UDF list is interesting in the VizieR context. In particular
the healpix and proper motion functions.<br>
I think that ivo_transform is as important than those already
listed with ivo prefix (may be more) - <br>
In fact I expected a standard-ADQL function, but I imagine that
you have already discussed about that - <br>
</p>
<p>Just to clarify ( when coordinate syst. is not in parameter): I
imagine that we use the coord. syst. of the table in ADQL region ?</p>
<p>And what about crossmatch? is it expected (recommended?
required?) to make the change of coordinate in background? <br>
(and how to proceed when coord. syst. is unknown? (e.g. upload)).
<br>
I haven't seen this point in the ADQL document - may be it could
be useful ?<br>
</p>
<br>
About the ivo_transform function : I am agree with the gavo syntax
including the equinox (in option).<br>
<p>In VizieR, we have ~15 different coordinate systems with
different equinox (some are very exotics: e.g.: RAB1770, catalogue
J/A+A/567/A26)</p>
<p>Today, we computed ICRS column for VizieR tables - but not for
all.<br>
The change of coord. syst. in TAPVizieR is based only on the
system without equinox. .. So, there are ~ 100 tables not treated
yet which could be fixed with equinox.</p>
<p><br>
</p>
<p>Gilles<br>
</p>
<p><br>
</p>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 18/10/2019 12:00, <a
class="moz-txt-link-abbreviated"
href="mailto:dal-request@ivoa.net">dal-request@ivoa.net</a>
wrote:<br>
</div>
<blockquote cite="mid:mailman.3.1571392801.4826.dal@ivoa.net"
type="cite">
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Today's Topics:
1. Coordinate system in ADQL (gilles landais)
2. Re: Coordinate system in ADQL (Markus Demleitner)
----------------------------------------------------------------------
Message: 1
Date: Thu, 17 Oct 2019 15:25:50 +0200
From: gilles landais <a class="moz-txt-link-rfc2396E" href="mailto:gilles.landais@astro.unistra.fr"><gilles.landais@astro.unistra.fr></a>
To: <a class="moz-txt-link-abbreviated" href="mailto:dal@ivoa.net">dal@ivoa.net</a>
Subject: Coordinate system in ADQL
Message-ID: <a class="moz-txt-link-rfc2396E" href="mailto:79fe4511-1097-e316-dcfb-6af521582188@astro.unistra.fr"><79fe4511-1097-e316-dcfb-6af521582188@astro.unistra.fr></a>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
Dear IVOA members !
Following the last IVOA meeting and about the new ADQL version.
Coordinate System had been deprecated from the ADQL region. This
capability was may be not very used, and was may be ambiguous. However
to change the coordinate system was used in VizieR.
Moreover, there is not today a pivot coordinate system used for all
tables in all data-centers. I am agree that coordinate System could be
an option, but in my opinion, to remove it without any alternatives will
impoverish ADQL.
If coordinate system in option is rejected, we could also add a function
such as the function proposed by Markus in Gavo to make possible the
change of coordinate System:
gavo_transform(from_sys TEXT, to_sys TEXT, geo GEOMETRY) -> GEOMETRY
So, I ask IVOA people to consider this capability as a ADQL standard (as
a function - may be optional).
Regards,
Gilles Landais (CDS)
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Message: 2
Date: Fri, 18 Oct 2019 09:59:35 +0200
From: Markus Demleitner <a class="moz-txt-link-rfc2396E" href="mailto:msdemlei@ari.uni-heidelberg.de"><msdemlei@ari.uni-heidelberg.de></a>
To: <a class="moz-txt-link-abbreviated" href="mailto:dal@ivoa.net">dal@ivoa.net</a>
Subject: Re: Coordinate system in ADQL
Message-ID: <20191018075935.pxt2hfua5ixv5gg5@victor>
Content-Type: text/plain; charset=utf-8
Hi Gilles,
On Thu, Oct 17, 2019 at 03:25:50PM +0200, gilles landais wrote:
</pre>
<blockquote type="cite">
<pre wrap="">If coordinate system in option is rejected, we could also add a function
such as the function proposed by Markus in Gavo to make possible the change
of coordinate System:
gavo_transform(from_sys TEXT, to_sys TEXT, geo GEOMETRY) -> GEOMETRY
So, I ask IVOA people to consider this capability as a ADQL standard (as a
function - may be optional).
</pre>
</blockquote>
<pre wrap="">The current proposal is to have a list of common UDFs in a separate
list rather than in the ADQL spec itself, and I guess the ADQL
editor(s) will be grateful if we try to keep it this way.
A proposal for that separate list is in
<a class="moz-txt-link-freetext" href="http://ivoa.net/documents/udf-catalogue/">http://ivoa.net/documents/udf-catalogue/</a>, and I guess it should go to
RFC after the next TCG.
Which means this is the perfect moment to add a proposal -- if VizieR
and DaCHS agree on this, I'd say that's a good base for making this
and "agreed" UDF and call it ivo_transform.
As usual, the devil is in the details, namely what people can put
into the system strings. And how they can figure out what systems a
given service supports -- I suppose VizieR will want to support
legacy equatorial systems at various equinoxes, for instance, which
DaCHS at least so far doesn't.
So, here's a proposal for what the UDF catalog might say:
ivo_transform(from_sys TEXT, to_sys TEXT, geo GEOMETRY) -> GEOMETRY
The function transforms ADQL geometries between various reference
systems. geo can be a POINT, a CIRCLE, or a POLYGON, and the function
will return a geometry of the same type. From_sys and to_sys must
be literal strings (i.e., they cannot be computed through
expressions or be taken from database columns).
Note that the epoch is not changed by this function (i.e., no
proper motions are applied).
Where services support reference frames from the IVOA vocabulary
of reference frames (<a class="moz-txt-link-freetext" href="http://www.ivoa.net/rdf/refframe">http://www.ivoa.net/rdf/refframe</a>), terms
from that list should be used in from_sys and to_sys. The
description of the TAPRegExt feature declaring support for
ivo_transform should enumerate the frames supported by a service.
Using an unknown frame should be an error, and the accompanying
error message should again enumerate the strings understood by a
service.
Pointing to the refframe vocabulary certainly isn't good enough for
frames that need an equinox. We could leave that to the services,
but then it's probably better if we can give some sensible
guidelines. I could see either
Referencence frames requiring an equinox append it after a single
blank. Use B to indicate a Besselian, J to indicate a Julian
epoch, e.g., "FK4 B1950" or "FK5 J1975.0"
(which would provide maximum flexibility) or
For legacy reference frames, it is recommended to just use the
equinox with B indicating a Besselian, J to indicating a Julian
epoch.
This latter thing would help with, for instance I/122/bd a.k.a.
Bonner Durchmusterung -- though, of course, you could name its
(popular, in its day) frame in the first scheme by saying EQUATORIAL
B1855.0 just as well.
Out of curiosity: Gilles, do you have any idea on how many different
frames there are in VizieR?
-- Markus
------------------------------
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</pre>
</blockquote>
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