<div dir="ltr"><div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Apr 3, 2020 at 5:04 AM Laurent MICHEL <<a href="mailto:laurent.michel@astro.unistra.fr">laurent.michel@astro.unistra.fr</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Hello,<br>
<br>
FITS paper II and III are listed in the draft (page 6) but not FITS <br>
paper IV (time representation).<br>
It's a bit odd.<br>
To me, time transformations are symmetric with e.g. spectral coordinate <br>
transformations, even if they are less used in FITS files.<br></blockquote><div><br></div><div>Interesting side-note.. the Time paper was "<span style="color:rgb(0,0,0);font-family:Arial,"Avant Gard","Sans Serif"">Approved by the IAUFWG in June 2014".. just about the time Arnold started the STC2 project.</span></div><div><span style="color:rgb(0,0,0);font-family:Arial,"Avant Gard","Sans Serif"">That may have contributed to why it is not in the current scope.</span></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Le 02/04/2020 à 17:35, David Berry a écrit :<br>
> On Thu, 2 Apr 2020 at 15:55, CresitelloDittmar, Mark<br>
> <<a href="mailto:mdittmar@cfa.harvard.edu" target="_blank">mdittmar@cfa.harvard.edu</a>> wrote:<br>
>><br>
>><br>
>> You mean like DATE => MJD? GMT - PST?<br>
yes I do<br>
<br>
>> I think these are in the same level as ENERGY-FREQUENCY-WAVELENGTH, which are really standardized transforms which are basically considered different forms of the same value. Which is why they are in the Coords model as different 'flavors' of Time coordinate rather than having a single time coordinate and using transforms to convert.<br>
You need a transform to go from a flavor to another.<br>
If I want to use TRANSF to model e.g. a ground segment processing, I <br>
might have a step converting spacecraft time to earth time.<br>
This is very similar with converting pixels to RA/DEC by using attitude <br>
data among other things or converting spectrometer channels to kEv.<br></blockquote><div><br></div><div>I'll basically echo Arnold's statement. The conversion from one to the other is a form of transform I suppose, but not one that you will export to a serialization. I don't expect anyone will define a MJD column with a formal Transform expression from a DATE column. Instead, applications/implementations will implement a Time type and use the algorithm for making that conversion under-the-hood. At the very least, I'd say we don't need it in this version of the model, and come up with a use-case where that would be necessary and implement that as a follow-up project.</div><div> </div><div>I'm happy to add some clarifying text about the depth of transform support in this model (ie: not having equatorial-galactic, energy-wavelength, date-hjd (that's for you Arnold! nice to see you're still watching.) ).</div><div><br></div><div>Mark</div><div><br></div><div><br></div></div></div></div>