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<div class="moz-cite-prefix">Dear Alberto,</div>
<div class="moz-cite-prefix">I quote Arnold (2015 Apr 30)</div>
<div class="moz-cite-prefix">
<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 class="moz-cite-prefix">You could have a different velocity map
for the two lines in the same dataset.</div>
<div class="moz-cite-prefix">Cheers</div>
<div class="moz-cite-prefix">François <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Le 22/02/2023 à 17:06, Alberto Micol a
écrit :<br>
</div>
<blockquote type="cite"
cite="mid:3993FD07-2D9C-4C64-AEB9-182C7F03B0DA@eso.org">
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Many
thanks François,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">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 ?”<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Could
you explain that with more words, maybe giving an example?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">To
explain why I do not understand that sentence, I give you an
example of a cube I have at hand here.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">In
my case a velocity cube is a FITS cube with the third axis
defined as:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">CTYPE3
= ‘VRAD’<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">CUNIT3
= ‘m/s’<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">CD3_3_
= 250<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">CRVAL3
= 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">CRPIX3
= 141<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">NAXIS3
= 281<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">That
is enough to state that:
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">V_min
= -35000 m/s<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">V_max
= +35000 m/s<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Many
thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Alberto<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:12.0pt;color:black">From: </span></b><span
style="font-size:12.0pt;color:black">BONNAREL FRANCOIS
<a class="moz-txt-link-rfc2396E" href="mailto:francois.bonnarel@astro.unistra.fr"><francois.bonnarel@astro.unistra.fr></a><br>
<b>Date: </b>Wednesday, 22 February 2023 at 16:46<br>
<b>To: </b>alberto micol
<a class="moz-txt-link-rfc2396E" href="mailto:amicol.ivoa@googlemail.com"><amicol.ivoa@googlemail.com></a>, Alberto Micol
<a class="moz-txt-link-rfc2396E" href="mailto:amicol@eso.org"><amicol@eso.org></a><br>
<b>Cc: </b><a class="moz-txt-link-rfc2396E" href="mailto:dal@ivoa.net">"dal@ivoa.net"</a> <a class="moz-txt-link-rfc2396E" href="mailto:dal@ivoa.net"><dal@ivoa.net></a>, Data
Models mailing list <a class="moz-txt-link-rfc2396E" href="mailto:dm@ivoa.net"><dm@ivoa.net></a><br>
<b>Subject: </b>Re: ObsCore for velocity cubes<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
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7.5pt">
<p class="MsoNormal"><span
style="font-size:10.0pt;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 class="moz-txt-link-abbreviated" href="mailto:francois.bonnarel@astro.unistra.fr">francois.bonnarel@astro.unistra.fr</a>]</span></strong><span
style="color:black">. If it looks suspicious,
please report it to <a class="moz-txt-link-abbreviated" href="mailto:phishing@eso.org">phishing@eso.org</a>.</span><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="display:none"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="line-height:7.5pt"><span
style="font-size:7.5pt"> <o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span style="color:white">Dear Albe</span>rto,
all,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></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.<o:p></o:p></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"
moz-do-not-send="true" class="moz-txt-link-freetext">http://mail.ivoa.net/pipermail/dm/2015-April/005147.html</a>
and
<a
href="http://mail.ivoa.net/pipermail/dm/2015-April/005168.html"
moz-do-not-send="true" class="moz-txt-link-freetext">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"
moz-do-not-send="true" class="moz-txt-link-freetext">http://mail.ivoa.net/pipermail/dm/2015-May/005174.html</a><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"> The conclusion at that time was
that we didn't have to extend ObsCore this way eventually.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> For several reasons.<o:p></o:p></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.<o:p></o:p></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<o:p></o:p></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 ?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> ---> ObsCore will become
really complex to manage and fill in these situations<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"> Considering your use case
Alberto, I think we have two distinguish two steps<o:p></o:p></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"<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></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.
<o:p></o:p></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.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Cheers<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">François<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 1Le 22/02/2023 à 11:33, alberto micol a
écrit :<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">Very well, thanks both Markus and Pat. <o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">So, yes, we need a v_resolution, and it
must be in fixed units.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Taking the Greisen et al. default, this
is [m/s].<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">We though need the fravergy UCD to be
able to discriminate the different velocity flavours.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Is em_ucd the correct field to use? <o:p></o:p></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,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">that’s why I need your confirmation on
this)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Thanks!<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Alberto<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<div>
<div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal">On 21 Feb 2023, at 21:11,
Alberto Micol <<a href="mailto:amicol@eso.org"
moz-do-not-send="true"
class="moz-txt-link-freetext">amicol@eso.org</a>>
wrote:<o:p></o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica">Hi
James,</span><span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica">em_ucd
required</span><span style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica">Cheers,</span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica">Alberto</span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Helvetica"> </span><span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div style="border:none;border-top:solid windowtext
1.0pt;padding:3.0pt 0cm 0cm
0cm;border-top-color:rgb(181, 196, 223)">
<div>
<p class="MsoNormal"><b><span
style="font-size:12.0pt">From:<span
class="apple-converted-space"> </span></span></b><span
style="font-size:12.0pt">"Dempsey, James
(IM&T, Black Mountain)" <<a
href="mailto:James.Dempsey@csiro.au"
moz-do-not-send="true"><span
style="color:purple">James.Dempsey@csiro.au</span></a>><br>
<b>Date:<span class="apple-converted-space"> </span></b>Thursday,
16 February 2023 at 00:21<br>
<b>To:<span class="apple-converted-space"> </span></b>Alberto
Micol <<a href="mailto:amicol@eso.org"
moz-do-not-send="true"><span
style="color:purple">amicol@eso.org</span></a>>,
"<a href="mailto:dal@ivoa.net"
moz-do-not-send="true"><span
style="color:purple">dal@ivoa.net</span></a>"
<<a href="mailto:dal@ivoa.net"
moz-do-not-send="true"><span
style="color:purple">dal@ivoa.net</span></a>><br>
<b>Subject:<span
class="apple-converted-space"> </span></b>Re:
ObsCore for velocity cubes</span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<table class="MsoNormalTable" style="width:100.0%"
width="100%" cellspacing="0" cellpadding="0"
border="0">
<tbody>
<tr>
<td style="border:solid orange
1.0pt;border-left:solid orange
6.0pt;background:white;padding:7.5pt 7.5pt
7.5pt 7.5pt;background-position:initial
initial;background-repeat:initial initial">
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;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"
moz-do-not-send="true"><span
style="color:purple">prvs=40330730a=James.Dempsey@csiro.au</span></a>]</span></strong>. If
it looks suspicious, please report
it to<span
class="apple-converted-space"> </span><a
href="mailto:phishing@eso.org"
moz-do-not-send="true"><span
style="color:purple">phishing@eso.org</span></a>.</span></span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:Helvetica;display:none"><o:p> </o:p></span></p>
<table class="MsoNormalTable" cellspacing="0"
cellpadding="0" border="0">
<tbody>
<tr style="height:7.5pt">
<td style="width:100.0%;padding:0cm 0cm 0cm
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:10.0pt"><o:p></o:p></span></p>
</div>
</td>
</tr>
</tbody>
</table>
<div>
<p class="MsoNormal"><span style="color:white">Hi
Alberto</span>,<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal">At CASDA we support cutouts
of velocity spectral line cubes.<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<ul style="margin-top:0cm" type="disc">
<li class="MsoListParagraph"
style="margin-top:0cm;margin-bottom:0cm;margin-bottom:.0001pt;mso-list:l0
level1 lfo1">
v_resolution – value of CDELT3 or CDELT4<span
style="font-size:10.0pt"> <o:p></o:p></span></li>
<li class="MsoListParagraph"
style="margin-top:0cm;margin-bottom:0cm;margin-bottom:.0001pt;mso-list:l0
level1 lfo1">
v_unit – although this should always be m/s<span
style="font-size:10.0pt"> <o:p></o:p></span></li>
</ul>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<div>
<div>
<p class="MsoNormal">Cheers,<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><b><span
style="color:#00A9CE">James Dempsey</span></b><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt">Senior Developer <span
class="apple-converted-space"> </span>|
CSIRO </span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><a
href="mailto:james.dempsey@csiro.au"
moz-do-not-send="true"><span
style="font-size:9.0pt;color:purple">james.dempsey@csiro.au</span></a><span
style="font-size:9.0pt"> <span
class="apple-converted-space"> </span>|
02 6214 2912</span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div style="border:none;border-top:solid windowtext
1.0pt;padding:3.0pt 0cm 0cm
0cm;border-top-color:rgb(181, 196, 223)">
<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span
style="font-size:12.0pt">From:<span
class="apple-converted-space"> </span></span></b><span
style="font-size:12.0pt">dal <<a
href="mailto:dal-bounces@ivoa.net"
moz-do-not-send="true"
class="moz-txt-link-freetext">dal-bounces@ivoa.net</a>>
on behalf of alberto micol <<a
href="mailto:amicol.ivoa@googlemail.com"
moz-do-not-send="true"
class="moz-txt-link-freetext">amicol.ivoa@googlemail.com</a>><br>
<b>Date:<span class="apple-converted-space"> </span></b>Thursday,
16 February 2023 at 12:02 am<br>
<b>To:<span class="apple-converted-space"> </span></b><a
href="mailto:dal@ivoa.net"
moz-do-not-send="true"
class="moz-txt-link-freetext">dal@ivoa.net</a>
<<a href="mailto:dal@ivoa.net"
moz-do-not-send="true"
class="moz-txt-link-freetext">dal@ivoa.net</a>><br>
<b>Subject:<span class="apple-converted-space"> </span></b>ObsCore
for velocity cubes</span><span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal">Dear ObsCorers,<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Let me call them “velocity
cubes”...<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Here my use case…<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">At ESO we need to support
cutouts of velocity cubes.<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">we query ivoa.ObsCore.<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<blockquote
style="margin-left:30.0pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<div>
<div>
<p class="MsoNormal">Shortly summarised, the
velocity can be either:<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
</blockquote>
<div>
<ul style="margin-top:0cm" type="disc">
<ul style="margin-top:0cm" type="circle">
<li class="MsoNormal" style="mso-list:l1
level2 lfo2">a radio (VRAD), <span
style="font-size:10.0pt">
<o:p></o:p></span></li>
<li class="MsoNormal" style="mso-list:l1
level2 lfo2">an optical (VOPT), <span
style="font-size:10.0pt">
<o:p></o:p></span></li>
<li class="MsoNormal" style="mso-list:l1
level2 lfo2">a relativistic velocity
(ZOPT), <span style="font-size:10.0pt">
<o:p></o:p></span></li>
<li class="MsoNormal" style="mso-list:l1
level2 lfo2">a generic apparent velocity
(VELO).<span style="font-size:10.0pt">
<o:p></o:p></span></li>
</ul>
</ul>
</div>
<blockquote
style="margin-left:30.0pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The velocity unit is m/s.<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
</blockquote>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">What would then be needed
in ObsCore is:<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">v_min<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">v_max<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">but also, in case of radio
velocity cube:<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">f_min<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">f_max (getting these from
the RADIO extension)<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">f_rest = RESTFRQ<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">and, in case of a optical
or relativistic velocity cube<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">em_rest = RESTWAV<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">(we already have em_min,
em_max)<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The em_resolv_power should
then be set to:<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> lambda
freq c<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> ——————— = ————— = —————<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> delta lambda
delta freq 2 * delta_v<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">The UCD for the velocity
should then be:<span style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<pre>spect.dopplerVeloc.opt<o:p></o:p></pre>
<div>
<pre>spect.dopplerVeloc.radio<o:p></o:p></pre>
<div>
<div>
<p class="MsoNormal">unsure what it should
be for the relativistic case.<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">and would allow astronomer
to search the velocity cubes with certain
characteristics using ObsCore.<span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">What do you think? <span
style="font-size:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></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:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"> <span
style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">Eager to know what you
think, <span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">Cheers,<span
style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">Alberto<span
style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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</blockquote>
<p><o:p> </o:p></p>
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