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<p class="MsoNormal"><span style="font-size:12.0pt">Hi Markus, et al.,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Thanks for the thorough write-up. I think I’m on board with the concept, and happy to help shepherd it through the VOTable change process, but I do have a few questions and comments.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:12.0pt">In the note PDF, tables 1 and 2 are awkwardly interspersed with the content describing the TIMESYS attributes. Even a footnote is split across two pages.<o:p></o:p></span></li></ol>
<p class="MsoListParagraph"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="2" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:12.0pt">My domain knowledge on this is weak, so I will have to defer to others for the final word, but from a computing point of view, I don’t yet understand
the need for the timeorigin attribute. Is it just a convenience for values that are offsets, or is it a fundamental part of the time scale or system?
<o:p></o:p></span></li></ol>
<p class="MsoListParagraph"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="2" type="1">
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<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level2 lfo1"><span style="font-size:12.0pt">If it is just a convenience, is that really necessary? The full description of timeorigin made me pretty concerned as a client developer (i.e., I’d
be disinclined to implement support for it), so I’d like to be assured that the attribute and its use are well-defined and worthwhile.<o:p></o:p></span></li></ol>
</ol>
<p class="MsoListParagraph"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="2" type="1">
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<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level2 lfo1"><span style="font-size:12.0pt">Although in the astropy Time class (<a href="http://docs.astropy.org/en/stable/api/astropy.time.Time.html#astropy.time.Time.SCALES">http://docs.astropy.org/en/stable/api/astropy.time.Time.html#astropy.time.Time.SCALES</a>
) I did see clear use of time scales nearly matching those proposed here, I didn’t see any use of a time origin. Again, this is probably just my ignorance on how times are defined and used, but:<o:p></o:p></span></li></ol>
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<p class="MsoListParagraph"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.5in;text-indent:-1.5in;mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1">
<![if !supportLists]><span style="font-size:12.0pt"><span style="mso-list:Ignore"><span style="font:7.0pt "Times New Roman"">
</span>i.<span style="font:7.0pt "Times New Roman""> </span></span></span><![endif]><span style="font-size:12.0pt">An implementation showing how those values would be used with astropy would be extraordinarily helpful to me to demonstrate the purpose and
usage of timeorigin.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.5in;text-indent:-1.5in;mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1">
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</span>ii.<span style="font:7.0pt "Times New Roman""> </span></span></span><![endif]><span style="font-size:12.0pt">If the attribute is needed, I’d still need to be convinced that the convenience values JD-origin and MJD-origin are worth the added complexity.<o:p></o:p></span></p>
<p class="MsoListParagraph"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="3" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:12.0pt">I have never been super happy with the context-dependent meaning of “ref” (it can refer to a COOSYS, TIMEDEF, TABLE, GROUP, etc., depending on where
you are, and not all the reference semantics are clear). I realize we’re kind of stuck with that concept for now, so I’ll just ask the dumb question of whether or not a FIELD that references a TIMEDEF may also want to reference something else such as a GROUP.<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Thanks for considering my questions,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Tom<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal" style="margin-left:.5in"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black"><apps-bounces@ivoa.net> on behalf of Markus Demleitner <msdemlei@ari.uni-heidelberg.de><br>
<b>Date: </b>Tuesday, December 4, 2018 at 3:52 AM<br>
<b>To: </b>Applications WG <apps@ivoa.net>, "voevent@ivoa.net" <voevent@ivoa.net><br>
<b>Subject: </b>Re: Timesys note review<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Hi Steve, Hi Apps,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On Thu, Nov 29, 2018 at 10:30:51AM -0800, Steve Allen wrote:<o:p></o:p></p>
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<blockquote style="border:none;border-left:solid #B5C4DF 4.5pt;padding:0in 0in 0in 4.0pt;margin-left:3.75pt;margin-right:0in" id="MAC_OUTLOOK_ATTRIBUTION_BLOCKQUOTE">
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<p class="MsoNormal" style="margin-left:.5in">As Rob Seaman reiterates, very few observations have timestamps that<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">merit the distinction between UT1 and UT. UT1 implies that some<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">special care has been taken in post-observation data reduction. There<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">are no tabulations with self-consistent re-reductions of the<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">difference between UT1 and the available time signals from before the<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">change from FK3 catalog to FK4 catalog on 1962-01-01.<o:p></o:p></p>
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</blockquote>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">I've changed the former UT1 in that table to:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> \item[UT] Earth rotation time. We do not distinguish between UT0, UT1,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> and UT2; applications requiring this level of precision need additional<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> metadata. This should also be used to label GMT times in datasets covering
<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> dates before 1972-01-01.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">(volute rev. 5251) and removed the former language on GMT in UTC. Is<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">that minimally acceptable?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Also, I've put in François' and Mark's proposal of M?JD-origin both<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">into the text and the draft VOTable schema. Putting it in convinced<o:p></o:p></p>
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<div>
<p class="MsoNormal" style="margin-left:.5in">me again that it's probably not a good deal in terms of standard<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">effort vs. possible benefit, but since nobody spoke out against it so<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">far, it's in now (rev. 5252).<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
</div>
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<p class="MsoNormal" style="margin-left:.5in">A pre-built draft document is still at<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><a href="http://docs.g-vo.org/timesys-draft.pdf">http://docs.g-vo.org/timesys-draft.pdf</a>, the draft schema is in volute<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">at<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><a href="https://volute.g-vo.org/svn/trunk/projects/time-domain/timesysnote/VOTable-1.4-draft.xsd">https://volute.g-vo.org/svn/trunk/projects/time-domain/timesysnote/VOTable-1.4-draft.xsd</a><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">-- unless there's more feedback, this would be what I'd submit as<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">version 1.1 (except I'll update the frame/refpos enumerations in the<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">schema).<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Thanks for the feedback, everyone,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> Markus<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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