[CF-metadata] How to define time coordinate in GPS?

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 3 Jun 2015 15:47:21 +0100

Dear Chris

> While not happy, would you agree to introduce gregorian_utc, gregorian_gps,
> gregorian_nls, define gregorian = gregorian_nls and deprecate it?
>
> seems reasonable to me.

Good.

> > I think we
> > should omit gregorian_tai (although it's been instructive to discuss it)
> > since it's not been asked for yet.
>
> fine with me -- I don't need it :-) -- though I thought that was the start
> of this entire discussion.

The title of the thread is GPS. But maybe it was TAI. Please could anyone who
needs TAI speak up!

> > > >so the Calendar is ONLY for defining the reference
> > > >timestamp in the units.
> >
> > I don't agree still with this. The calendar specifies the time system for
> > the reference time-stamp and the decoded time-coordinates,
>
> I'm confused -- in the file, there are ONLY encoded time on the time
> coordinates. How it gets decoded is entirely up to the data user -- they
> can put it any calendar they want. I suppose your point is that the data
> provider is specifying how the time coordinate is intended to be used --
> which is fine. I can't imagine it would cause any problems to think of it
> that way.

Yes, that's what I meant. If the decoding is done as specified by the method
implied by the calendar, the timestamps are (a) correct for and (b) should be
interpreted as being in that calendar. As a result of this discussion I see
that (a) and (b) are not the same, but they belong together.

> > I have learned,
> > and it also specifies how the translation is done.
>
> by whom? when? my point is that the translation is up to the data user --
> it's not in the file.

By identifying the calendar, the data-producer is (a) stating the method
which was used to encode the time coordinates (b) instructing the data-user to
use the reverse of that method to decode them into timestamps.

Best wishes

Jonathan
Received on Wed Jun 03 2015 - 08:47:21 BST