<div dir="ltr"><div><div><div><div>Since MJD is absolute, the client should ignore the timeOrigin. Actually, it should not even look to see whether there is one.<br><br></div><div>In terms of implementation:<br></div>The common implementation of time is to keep it as either JD or MJD (my code uses MJD, the JPL ephemeris uses JD), as either two doubles or an integer and a double.<br></div>JD and MJD times would then need either nothing or the JD-MJD fixed offset in order to be stored; ISOTime requires a little more; but only when a TimeOffset if provided would the code actually look for a timeOrigin value.<br></div>Or, if that feels more comfortable, you can (arbitrarily) assign a default value for the timeOrigin; can be zero or 10^10 or your favorite prime number.<br><br></div> - Arnold<br></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr">-------------------------------------------------------------------------------------------------------------<br>Arnold H. Rots Chandra X-ray Science Center<br>Smithsonian Astrophysical Observatory tel: +1 617 496 7701<br>60 Garden Street, MS 67 fax: +1 617 495 7356<br>Cambridge, MA 02138 <a href="mailto:arots@cfa.harvard.edu" target="_blank">arots@cfa.harvard.edu</a><br>USA <a href="http://hea-www.harvard.edu/~arots/" target="_blank">http://hea-www.harvard.edu/~arots/</a><br>--------------------------------------------------------------------------------------------------------------<br><br></div></div></div>
<br><div class="gmail_quote">On Thu, Apr 12, 2018 at 6:23 PM, CresitelloDittmar, Mark <span dir="ltr"><<a href="mailto:mdittmar@cfa.harvard.edu" target="_blank">mdittmar@cfa.harvard.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote"><span class="">On Thu, Apr 12, 2018 at 5:18 PM, Arnold Rots <span dir="ltr"><<a href="mailto:arots@cfa.harvard.edu" target="_blank">arots@cfa.harvard.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div><div><div>No, the timeOrigin is only REQUIRED in a TimeFrame if it is referenced by a TimeOffset.<br></div>So, both the TimeOffset and the timeOrigin can (and should!) refer to the same TimeFrame.<br></div>(they should, because specifying the origin in a different TimeFrame is asking for trouble)<br><br></div></div></div></div></blockquote><div><br></div></span><div>So, when a client reads a TimeOffset with timeOrigin, loads that (MJD) and sees it references the same TimeFrame with a timeOrigin (itself), what is the client supposed to do?<br></div><div>Since timeOrigin is only REQUIRED for TimeOffset, can I have a data column that is Time in MJD, and have it refer to a TimeFrame with a TimeOrigin? If so, what does the client do with that since MJD is absolute?<br></div><span class=""><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div></div>It does mean that TimeOffsets that use different timeOrigins need to reference different TimeFrames.<br></div>That is not a problem, since most TimeOffset-based time series will use the same timeOrigin.<span class="m_-2516573041359785892HOEnZb"><font color="#888888"><br><br></font></span></div><span class="m_-2516573041359785892HOEnZb"><font color="#888888"> - Arnold<br></font></span></div></blockquote></span></div></div></div>
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