[CF-metadata] Temporal nitpicks. Was: CF-metadata Digest, Vol 161, Issue 3

From: Jim Biard <jbiard>
Date: Thu, 22 Sep 2016 15:06:56 -0400

Hi.

So I went and dug into the source code for UDUNITS and UDUNITS-2. Both
versions of UDUNITS allow a wide variety of epoch date/time formulations
with and without space delimiters between just about any of the
components, with and without leading zeros, with and without a 'T'
between the date and the time, and allowing 'UTC', 'GMT', or 'Z' (in
addition to the 'classical' YYYY-MM-DD hh:mm:ss[.sss] [-]h:mm form).

So on one level this seems like a case for modifying the documentation
without a formal change to the convention. Except...

The CF time convention is out there already with the pretty well
understood classical form that I mentioned above. Software written to
that form could very well break if a different form is used. In
addition, there is an issue that connects with all of this that I've
been horribly slow to write a ticket on. It has to do with time systems
other than UTC, such as native GPS and TAI, that don't have leap seconds.

At the very minimum, we need to make it very clear that times without
offsets or designators ARE NOT local times. This is baked deeply enough
into CF and existing data sets that I don't see any clean way to go with
ISO8061.

This leads me to think that any change should be considered a change to
the time convention, not just a document edit.

Grace and peace,

Jim

On 9/22/16 12:23 PM, Steve Emmerson wrote:
> On Thu, Sep 22, 2016 at 9:45 AM, Chris Barker <chris.barker at noaa.gov
> <mailto:chris.barker at noaa.gov>> wrote:
>
> I think UDUnits does not use a T but maybe it will accept it.
>
>
> UDUNITS accepts the "T" and can print it.
>
> Regards,
> Steve Emmerson
>
>
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Received on Thu Sep 22 2016 - 13:06:56 BST