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

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 27 Apr 2015 18:07:39 +0100

Dear Jim

> I don't think calendars are the right place to encode this. We could
> add a new "time_system" attribute where you would declare whether
> your time stamps and elapsed times were based on UTC, GPS, TAI, etc.
> If we take this route, we should require the elapsed times to encode
> leap seconds if the time system is UTC, and state that the default
> time system is UTC.

I think this is a calendar issue because the calendar is the set of rules
which translate between components of time (YMDhms) and elapsed time (in
fixed time units) since the reference time. Your later email seems to me
to be consistent with that. In the real world, the elapsed interval (expressed
e.g. as the number of seconds) between the ref YMDhms and the actual YMDhs
depends on whether your calendar includes leap seconds (UTC) or not (GPS).
It seems that GPS is the calendar likely to have been assumed in existing
CF datasets, so it would be logical to say that the default is the real-
world calendar without leap seconds. Have I misunderstood something? If we
regard this as a property of the calendar, we don't need a new attribute.

Best wishes

Jonathan
Received on Mon Apr 27 2015 - 11:07:39 BST