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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>
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<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 <francois.bonnarel@astro.unistra.fr><br>
<b>Date: </b>Wednesday, 22 February 2023 at 16:46<br>
<b>To: </b>alberto micol <amicol.ivoa@googlemail.com>, Alberto Micol <amicol@eso.org><br>
<b>Cc: </b>"dal@ivoa.net" <dal@ivoa.net>, Data Models mailing list <dm@ivoa.net><br>
<b>Subject: </b>Re: ObsCore for velocity cubes<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<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">[francois.bonnarel@astro.unistra.fr]</span></strong><span style="color:black">. If it looks suspicious, please report it to phishing@eso.org.</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"><span style="color:white">Dear Albe</span>rto, all,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<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>
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<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">http://mail.ivoa.net/pipermail/dm/2015-April/005147.html</a> and
<a href="http://mail.ivoa.net/pipermail/dm/2015-April/005168.html">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">http://mail.ivoa.net/pipermail/dm/2015-May/005174.html</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<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>
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<p class="MsoNormal"> For several reasons.<o:p></o:p></p>
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<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>
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<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>
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<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>
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<p class="MsoNormal"> ---> ObsCore will become really complex to manage and fill in these situations<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> Considering your use case Alberto, I think we have two distinguish two steps<o:p></o:p></p>
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<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>
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<p class="MsoNormal"><o:p> </o:p></p>
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<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>
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<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>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Cheers<o:p></o:p></p>
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<p class="MsoNormal">François<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"> 1Le 22/02/2023 à 11:33, alberto micol a écrit :<o:p></o:p></p>
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<p class="MsoNormal">Very well, thanks both Markus and Pat. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">So, yes, we need a v_resolution, and it must be in fixed units.<o:p></o:p></p>
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<p class="MsoNormal">Taking the Greisen et al. default, this is [m/s].<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">We though need the fravergy UCD to be able to discriminate the different velocity flavours.<o:p></o:p></p>
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<p class="MsoNormal">Is em_ucd the correct field to use? <o:p></o:p></p>
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<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>
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<p class="MsoNormal">that’s why I need your confirmation on this)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks!<o:p></o:p></p>
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<p class="MsoNormal">Alberto<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On 21 Feb 2023, at 21:11, Alberto Micol <<a href="mailto:amicol@eso.org">amicol@eso.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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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"><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"><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"><span style="color:purple">amicol@eso.org</span></a>>, "<a href="mailto:dal@ivoa.net"><span style="color:purple">dal@ivoa.net</span></a>" <<a href="mailto:dal@ivoa.net"><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>
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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"><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"><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"><span style="color:purple">phishing@eso.org</span></a>.</span></span><span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:white">Hi Alberto</span>,<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">At CASDA we support cutouts of velocity spectral line cubes.<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">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>
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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">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>
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<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>
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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">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>
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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">Cheers,<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="color:#00A9CE">James Dempsey</span></b><span style="font-size:10.0pt"><o:p></o:p></span></p>
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<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>
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<p class="MsoNormal"><a href="mailto:james.dempsey@csiro.au"><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>
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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" 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">dal-bounces@ivoa.net</a>> on behalf of
alberto micol <<a href="mailto:amicol.ivoa@googlemail.com">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">dal@ivoa.net</a> <<a href="mailto:dal@ivoa.net">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>
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<p class="MsoNormal">Dear ObsCorers,<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">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>
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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">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>
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<p class="MsoNormal">Let me call them “velocity cubes”...<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">Here my use case…<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">At ESO we need to support cutouts of velocity cubes.<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">Up to now our SODA interface supported spectra, images, and wavelength cubes;<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<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>
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<p class="MsoNormal">we query ivoa.ObsCore.<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">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>
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<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>
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<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>
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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">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>
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<p class="MsoNormal">Shortly summarised, the velocity can be either:<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<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">
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<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>
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<p class="MsoNormal">The velocity unit is m/s.<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">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>
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<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>
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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">What would then be needed in ObsCore is:<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">v_min<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">v_max<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">but also, in case of radio velocity cube:<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">f_min<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">f_max (getting these from the RADIO extension)<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">f_rest = RESTFRQ<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">and, in case of a optical or relativistic velocity cube<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">em_rest = RESTWAV<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">(we already have em_min, em_max)<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">The em_resolv_power should then be set to:<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"> lambda freq c<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"> delta lambda delta freq 2 * delta_v<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">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>
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<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>
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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">The UCD for the velocity should then be:<span style="font-size:10.0pt"><o:p></o:p></span></p>
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<pre>spect.dopplerVeloc.opt<o:p></o:p></pre>
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<pre>spect.dopplerVeloc.radio<o:p></o:p></pre>
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<p class="MsoNormal">unsure what it should be for the relativistic case.<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">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>
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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: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">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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