<div dir="ltr"><div>Thank you, Francois, for continuing to carry the message!</div><div><br></div><div>Cheers,</div><div><br></div><div> - Arnold<br></div><div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><br><div dir="ltr" style="margin-left:0pt"><table style="border:medium none;border-collapse:collapse"><colgroup><col width="445"><col width="275"></colgroup><tbody><tr style="height:90pt"><td style="border-color:rgb(255,255,255);border-style:solid;border-width:1pt;vertical-align:top;padding:5pt"><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:9.5pt;font-family:Arial;color:rgb(34,34,34);background-color:transparent;font-weight:700;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:pre-wrap">Arnold H Rots</span></p><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span 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style="font-size:9.5pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-weight:400;font-style:normal;font-variant:normal;text-decoration:underline;vertical-align:baseline;white-space:pre-wrap">Newsletter</span></a></p></td></tr></tbody></table></div></div></div></div></div></div></div></div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Feb 22, 2023 at 11:20 AM BONNAREL FRANCOIS <<a href="mailto:francois.bonnarel@astro.unistra.fr">francois.bonnarel@astro.unistra.fr</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<div>Dear Alberto,</div>
<div>I quote Arnold (2015 Apr 30)</div>
<div>
<blockquote type="cite">
<pre>I strongly urge to keep the two separate.
Yes, they have much in common, but they serve very different purposes.
And it is possible to create a 4-D cube where the 4th axis is actually a
spectral axis and the pixels are different lines (rest frequencies).
STC2 will treat the spectral and redshift/Doppler as distinct axes.
</pre>
</blockquote>
Now imagine you have Halpha and Hbeta lines in the same dataset
(MUSE cubes?). The may come from different regions and the
velocities will be different for both.</div>
<div>You could have a different velocity map
for the two lines in the same dataset.</div>
<div>Cheers</div>
<div>François <br>
</div>
<div><br>
</div>
<div>Le 22/02/2023 à 17:06, Alberto Micol a
écrit :<br>
</div>
<blockquote type="cite">
<div>
<p class="MsoNormal"><span>Many
thanks François,<u></u><u></u></span></p>
<p class="MsoNormal"><span><u></u> <u></u></span></p>
<p class="MsoNormal"><span>I
will think thouroughly through your message, but first I
would like to ask you to clarify the meaning of your
sentence: “As Arnold pointed at that time you have datasets
where you provide different doppler shift information at
different spectral coordinates. What are the radial velocity
bounds in that case ?”<u></u><u></u></span></p>
<p class="MsoNormal"><span>Could
you explain that with more words, maybe giving an example?<u></u><u></u></span></p>
<p class="MsoNormal"><span><u></u> <u></u></span></p>
<p class="MsoNormal"><span>To
explain why I do not understand that sentence, I give you an
example of a cube I have at hand here.<u></u><u></u></span></p>
<p class="MsoNormal"><span><u></u> <u></u></span></p>
<p class="MsoNormal"><span>In
my case a velocity cube is a FITS cube with the third axis
defined as:<u></u><u></u></span></p>
<p class="MsoNormal"><span>CTYPE3
= ‘VRAD’<u></u><u></u></span></p>
<p class="MsoNormal"><span>CUNIT3
= ‘m/s’<u></u><u></u></span></p>
<p class="MsoNormal"><span>CD3_3_
= 250<u></u><u></u></span></p>
<p class="MsoNormal"><span>CRVAL3
= 0<u></u><u></u></span></p>
<p class="MsoNormal"><span>CRPIX3
= 141<u></u><u></u></span></p>
<p class="MsoNormal"><span>NAXIS3
= 281<u></u><u></u></span></p>
<p class="MsoNormal"><span><u></u> <u></u></span></p>
<p class="MsoNormal"><span>That
is enough to state that:
<u></u><u></u></span></p>
<p class="MsoNormal"><span>V_min
= -35000 m/s<u></u><u></u></span></p>
<p class="MsoNormal"><span>V_max
= +35000 m/s<u></u><u></u></span></p>
<p class="MsoNormal"><span><u></u><u></u></span></p>
<p class="MsoNormal"><span>Many
thanks,<u></u><u></u></span></p>
<p class="MsoNormal"><span>Alberto<u></u><u></u></span></p>
<p class="MsoNormal"><span><u></u> <u></u></span></p>
<div style="border-color:rgb(181,196,223) currentcolor currentcolor;border-style:solid none none;border-width:1pt medium medium;padding:3pt 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:12pt;color:black">From: </span></b><span style="font-size:12pt;color:black">BONNAREL FRANCOIS
<a href="mailto:francois.bonnarel@astro.unistra.fr" target="_blank"><francois.bonnarel@astro.unistra.fr></a><br>
<b>Date: </b>Wednesday, 22 February 2023 at 16:46<br>
<b>To: </b>alberto micol
<a href="mailto:amicol.ivoa@googlemail.com" target="_blank"><amicol.ivoa@googlemail.com></a>, Alberto Micol
<a href="mailto:amicol@eso.org" target="_blank"><amicol@eso.org></a><br>
<b>Cc: </b><a href="mailto:dal@ivoa.net" target="_blank">"dal@ivoa.net"</a> <a href="mailto:dal@ivoa.net" target="_blank"><dal@ivoa.net></a>, Data
Models mailing list <a href="mailto:dm@ivoa.net" target="_blank"><dm@ivoa.net></a><br>
<b>Subject: </b>Re: ObsCore for velocity cubes<u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<table style="width:100%" width="100%" cellspacing="0" cellpadding="0" border="0">
<tbody>
<tr>
<td style="border-color:orange;border-style:solid;border-width:1pt 1pt 1pt 6pt;background:white;padding:7.5pt">
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">This
email was sent from outside of ESO from the address
<strong><span style="font-family:"Arial",sans-serif;color:black">[<a href="mailto:francois.bonnarel@astro.unistra.fr" target="_blank">francois.bonnarel@astro.unistra.fr</a>]</span></strong><span style="color:black">. If it looks suspicious,
please report it to <a href="mailto:phishing@eso.org" target="_blank">phishing@eso.org</a>.</span><u></u><u></u></span></p>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><span style="display:none"><u></u> <u></u></span></p>
<table cellspacing="0" cellpadding="0" border="0">
<tbody>
<tr style="height:7.5pt">
<td style="width:100%;padding:0cm;height:7.5pt" width="100%">
<p class="MsoNormal" style="line-height:7.5pt"><span style="font-size:7.5pt"> <u></u><u></u></span></p>
</td>
</tr>
</tbody>
</table>
<div>
<p class="MsoNormal"><span style="color:white">Dear Albe</span>rto,
all,<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal"> I come to this copying also to the dm
list (ObsCoire and extensions are dm stuff). As you may
remember this point was EXTENSIVELY discussed when we
upgraded ObsCore from 1.0 to 1.1.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> This discussion was mainly in
2014/2015. See for example these threads starting by
<a href="http://mail.ivoa.net/pipermail/dm/2015-April/005147.html" target="_blank">http://mail.ivoa.net/pipermail/dm/2015-April/005147.html</a>
and
<a href="http://mail.ivoa.net/pipermail/dm/2015-April/005168.html" target="_blank">http://mail.ivoa.net/pipermail/dm/2015-April/005168.html</a>
as well as
<a href="http://mail.ivoa.net/pipermail/dm/2015-May/005174.html" target="_blank">http://mail.ivoa.net/pipermail/dm/2015-May/005174.html</a><u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal"> The conclusion at that time was
that we didn't have to extend ObsCore this way eventually.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> For several reasons.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> - radial velocity or redshifts
derivation from spectral frequencies or wl are complex
things. querying between vel = 10 km/s and 60 km/s may give
different results according to the radial velocity (or
dopplershift) flavor. And if we add the constraint em_ucd =
vrad (or vopt, or ) then the query become really
specialised.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> - if the velocity cube is simply a
transform of the frequency/wavelength axis we still have to
select on wavelength because velocity cubes in radio domain
and velocity cube in optical domain are really different
things<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> - But generally speaking the
velocity axis is not ONLY a transform of the wavelength (or
frequency) axis, it provides different information. It is a
different axis (although related). As Arnold pointed at that
time you have datasets where you provide different doppler
shift information at different spectral coordinates. What
are the radial velocity bounds in that case ?<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> ---> ObsCore will become
really complex to manage and fill in these situations<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal"> Considering your use case
Alberto, I think we have two distinguish two steps<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> - data discovery (With
ObsTAP/ SIA) = it's probably enough to let the user know
that you have velocity cubes by providing the appropriate
values in em_ucd and em_unit (which are there to describe
the dataset content and not the spectral characterization).
We may think to add em_ref to give the wl of the reference
line. velocity limits will have to be transformed in
wavelength to fill the mandatory em_min/max anyway. With
this you already know that the data you discover by a
standard ObsCore (or radio extension) query are "'velocity
cubes"<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal"> - SODA cutouts : there , the
parameters you propose are useful. A discussion started
already some time ago to extend SODA . For example adding
pixel cutouts, or changing the projection or the spatial
sampling of the cutout. In this context we could also choose
to extract by forcing velocity constraints, when
appropro$iate.
<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> To do that we need
additional metadata (eg : the content of WCS, and this also
for the spectral axis). And for that, there is the old idea
to have a SODA mode providing full metadata, CADC already
implemented something like that. The velocity '"axis"
detailed flavor can be described this way if it exists. This
also has to be integrated in the SODA-next discussion. Some
more on this will come soon.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">Cheers<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">François<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> 1Le 22/02/2023 à 11:33, alberto micol a
écrit :<u></u><u></u></p>
</div>
<blockquote style="margin-top:5pt;margin-bottom:5pt">
<p class="MsoNormal">Very well, thanks both Markus and Pat. <u></u><u></u></p>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">So, yes, we need a v_resolution, and it
must be in fixed units.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">Taking the Greisen et al. default, this
is [m/s].<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">We though need the fravergy UCD to be
able to discriminate the different velocity flavours.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">Is em_ucd the correct field to use? <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">(Yes, I’m hit strongly by the confusion
of throwing untested features from a data model into a
relational mapping,<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">that’s why I need your confirmation on
this)<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">Thanks!<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">Alberto<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<div>
<div>
<blockquote style="margin-top:5pt;margin-bottom:5pt">
<div>
<p class="MsoNormal">On 21 Feb 2023, at 21:11,
Alberto Micol <<a href="mailto:amicol@eso.org" target="_blank">amicol@eso.org</a>>
wrote:<u></u><u></u></p>
</div>
<p class="MsoNormal"><u></u> <u></u></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Hi
James,</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Thanks
for the answer. I have a question/doubt
regarding the v_resolution and v_unit.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">ObsCore
already foresees the em_resolution, so I
originally thought we do not need the
v_resolution.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">But
now I am reconsidering this, because I think
(in the ObsCore standard we were not
super-clear regarding this) the units of
em_resolution are the ones provided by the
em_unit attribute. Different cubes could have
different em_units, and that means that
em_resolution could not be used to seamlessly
query across all possible cubes.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">If
the above is correct, then, yes, we need to
have a new field,</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">v_resolution,
with units fixed to e.g. m/s,</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">similarly
to the case of em_min/max always provided in
[m], whatever the value of the em_unit, to
support searches.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">In
which case, we do not need a v_unit, as
v_min/max are fixed in [m/s] and we already
have em_unit for the units encoded in the
cube.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Would
that make sense?</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Regarding
treating frequency cubes as velocity cubes
(and viceversa), </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">it
is indeed useful to provide characterisations
both in frequency and in velocity</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">(and
why not energy and wavelength), distinguishing
the different cases according to</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">the
value of the em_ucd, e.g., em.freq,
em.wl, em.energy (see ObsCore B.6.2), or</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">spect.dopplerVeloc.radio, spect.dopplerVeloc.opt, spect.dopplerVeloc.rel
(*) (see ObsCore B.6.2.6). </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">So
we would have:</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">em_ucd
required</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">v_resolution
required, fixed in m/s</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">em_unit
optional, expressing the unit encoded in the
cube for the spectral axis</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">em_resolution
optional, expressing the resolution in the
units used by the data cube</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">If
we converge on this, I could put together a
little document with a detailed proposal.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Would
that considered useful?</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Cheers,</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">Alberto</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">(*)
cross-standard issue: the
spect.dopplerVeloc.rel is mentioned in the
ObsCore standard, </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">but
it is not a recognised value in the current
UCD1+ standard.</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica">We
will need to act on this (Mireille?).</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div style="border-color:rgb(181,196,223) currentcolor currentcolor;border-style:solid none none;border-width:1pt medium medium;padding:3pt 0cm 0cm">
<div>
<p class="MsoNormal"><b><span style="font-size:12pt">From:<span> </span></span></b><span style="font-size:12pt">"Dempsey, James
(IM&T, Black Mountain)" <<a href="mailto:James.Dempsey@csiro.au" target="_blank"><span style="color:purple">James.Dempsey@csiro.au</span></a>><br>
<b>Date:<span> </span></b>Thursday,
16 February 2023 at 00:21<br>
<b>To:<span> </span></b>Alberto
Micol <<a href="mailto:amicol@eso.org" target="_blank"><span style="color:purple">amicol@eso.org</span></a>>,
"<a href="mailto:dal@ivoa.net" target="_blank"><span style="color:purple">dal@ivoa.net</span></a>"
<<a href="mailto:dal@ivoa.net" target="_blank"><span style="color:purple">dal@ivoa.net</span></a>><br>
<b>Subject:<span> </span></b>Re:
ObsCore for velocity cubes</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<table style="width:100%" width="100%" cellspacing="0" cellpadding="0" border="0">
<tbody>
<tr>
<td style="border-color:orange;border-style:solid;border-width:1pt 1pt 1pt 6pt;background:white;padding:7.5pt">
<div>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">Th<span style="color:black">is email was
sent from outside of ESO from the
address<strong><span style="font-family:"Arial",sans-serif">[<a href="mailto:prvs=40330730a=James.Dempsey@csiro.au" target="_blank"><span style="color:purple">prvs=40330730a=James.Dempsey@csiro.au</span></a>]</span></strong>. If
it looks suspicious, please report
it to<span> </span><a href="mailto:phishing@eso.org" target="_blank"><span style="color:purple">phishing@eso.org</span></a>.</span></span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><span style="font-size:9pt;font-family:Helvetica;display:none"><u></u> <u></u></span></p>
<table cellspacing="0" cellpadding="0" border="0">
<tbody>
<tr style="height:7.5pt">
<td style="width:100%;padding:0cm;height:7.5pt" width="100%">
<div>
<p class="MsoNormal" style="line-height:7.5pt"><span style="font-size:7.5pt"> </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</td>
</tr>
</tbody>
</table>
<div>
<p class="MsoNormal"><span style="color:white">Hi
Alberto</span>,<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal">At CASDA we support cutouts
of velocity spectral line cubes.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal">We currently require the user
to provide a BAND or CHANNEL parameter to the
SODA service which is translated by the service
to the velocity frame of the target cube. This
works, but requiring conversions on both the
client and server side isn’t ideal. Likewise, in
our ObsCore implementation only the em_ucd
indicates the cubes are in velocity but it would
certainly be useful to have full velocity
information for data discovery!<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal">The extension you outline
looks like it would work nicely for the same use
case in CASDA. However I think we should add the
following to fully describe the velocity axis
(as opposed to its translation into wavelength
for the base obscore).<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<ul style="margin-top:0cm" type="disc">
<li style="margin-top:0cm;margin-bottom:0.0001pt">
v_resolution – value of CDELT3 or CDELT4<span style="font-size:10pt"> <u></u><u></u></span></li>
<li style="margin-top:0cm;margin-bottom:0.0001pt">
v_unit – although this should always be m/s<span style="font-size:10pt"> <u></u><u></u></span></li>
</ul>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal">Another consideration is that
a lot of our users tend to use velocity to
interact with frequency cubes. So even for these
frequency cubes we might end up filling in
velocity metadata if the fields were defined.
Tools such as CARTA tend to automatically show
the spectral axis as velocity where it can, such
that many users would assume the cubes are in
velocity not frequency.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<div>
<div>
<p class="MsoNormal">Cheers,<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><b><span style="color:rgb(0,169,206)">James Dempsey</span></b><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9pt">Senior Developer <span> </span>|
CSIRO </span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"><a href="mailto:james.dempsey@csiro.au" target="_blank"><span style="font-size:9pt;color:purple">james.dempsey@csiro.au</span></a><span style="font-size:9pt"> <span> </span>|
02 6214 2912</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div style="border-color:rgb(181,196,223) currentcolor currentcolor;border-style:solid none none;border-width:1pt medium medium;padding:3pt 0cm 0cm">
<p class="MsoNormal" style="margin-bottom:12pt"><b><span style="font-size:12pt">From:<span> </span></span></b><span style="font-size:12pt">dal <<a href="mailto:dal-bounces@ivoa.net" target="_blank">dal-bounces@ivoa.net</a>>
on behalf of alberto micol <<a href="mailto:amicol.ivoa@googlemail.com" target="_blank">amicol.ivoa@googlemail.com</a>><br>
<b>Date:<span> </span></b>Thursday,
16 February 2023 at 12:02 am<br>
<b>To:<span> </span></b><a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a>
<<a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a>><br>
<b>Subject:<span> </span></b>ObsCore
for velocity cubes</span><span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<p class="MsoNormal">Dear ObsCorers,<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">I have received with much
interest the ObsCore extension for RADIO data,
thanks for that very clear document.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Would it be possible to
have a similar extension for cubes with
velocity as third axis (the other two being
the usual spatial ones)?<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Let me call them “velocity
cubes”...<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Here my use case…<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">At ESO we need to support
cutouts of velocity cubes.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Up to now our SODA
interface supported spectra, images, and
wavelength cubes;<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">to provide the user with
the SODA input parameters and their possible
MIN/MAX values<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">we query ivoa.ObsCore.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Now with the introduction
of velocity cubes, we would like to get the
necessary SODA input params also from ObsCore.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">We can certainly do so by
extending our own ObsCore table (ObsCore
allows to extend the table), but I was
wondering<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">if others have similar
needs, and see if we can agree with a common
ObsCore extension.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Velocity cubes should come
in a FITS format as described by Greisen et
al, 2006, so-called Paper 3.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<blockquote style="margin:5pt 0cm 5pt 30pt">
<div>
<div>
<p class="MsoNormal">Shortly summarised, the
velocity can be either:<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
</blockquote>
<div>
<ul style="margin-top:0cm" type="disc">
<ul style="margin-top:0cm" type="circle">
<li class="MsoNormal">a radio (VRAD), <span style="font-size:10pt">
<u></u><u></u></span></li>
<li class="MsoNormal">an optical (VOPT), <span style="font-size:10pt">
<u></u><u></u></span></li>
<li class="MsoNormal">a relativistic velocity
(ZOPT), <span style="font-size:10pt">
<u></u><u></u></span></li>
<li class="MsoNormal">a generic apparent velocity
(VELO).<span style="font-size:10pt">
<u></u><u></u></span></li>
</ul>
</ul>
</div>
<blockquote style="margin:5pt 0cm 5pt 30pt">
<div>
<div>
<p class="MsoNormal">The RESTFRQa (RESTWAVa)
keyword conveys the necessary reference
frequency (wavelength) to transform velocity
into frequency or wavelength. <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The velocity unit is m/s.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
</blockquote>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">SODA cutouts on the
velocity axis are usually formulated by
passing cuts already expressed in velocity<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">though it must be possible
to perform the conversions to and from
frequency/wavelength.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">What would then be needed
in ObsCore is:<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">v_min<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">v_max<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">but also, in case of radio
velocity cube:<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">f_min<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">f_max (getting these from
the RADIO extension)<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">f_rest = RESTFRQ<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">and, in case of a optical
or relativistic velocity cube<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">em_rest = RESTWAV<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">(we already have em_min,
em_max)<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The em_resolv_power should
then be set to:<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> lambda
freq c<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> ——————— = ————— = —————<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> delta lambda
delta freq 2 * delta_v<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">where delta_v is the CD3_3
in the cube (in the example of a cube with the
velocity on the third axis);<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">but I would also likely
accept a v_pixel_scale (= delta_v).<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The UCD for the velocity
should then be:<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<pre>spect.dopplerVeloc.opt<u></u><u></u></pre>
<div>
<pre>spect.dopplerVeloc.radio<u></u><u></u></pre>
<div>
<div>
<p class="MsoNormal">unsure what it should
be for the relativistic case.<span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">This would allow us at ESO
to implement SODA on top of ObsCore (as
already done for all other parameters)<span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">and would allow astronomer
to search the velocity cubes with certain
characteristics using ObsCore.<span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">What do you think? <span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">Is that doable? I think at
ESO we will simply start implementing the
above extra ObsCore parameters (unless you
suggest different names for that),<span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">while waiting to see if
there is more interest to build a proper
standard.<span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal"> <span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">Eager to know what you
think, <span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">Cheers,<span style="font-size:10pt"><u></u><u></u></span></p>
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<p class="MsoNormal">Alberto<span style="font-size:10pt"><u></u><u></u></span></p>
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</blockquote>
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<p class="MsoNormal"><u></u> <u></u></p>
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</blockquote>
<p><u></u> <u></u></p>
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<p><br>
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