On Thu, Sep 22, 2016 at 2:11 PM, Aaron Sweeney - NOAA Affiliate <
aaron.sweeney at noaa.gov> wrote:
> In case you and others are not already aware the Internet Engineering
> Task Force (IETF) RFC 3339: "Date and Time on the Internet: Timestamps,"
> circa 2002, (see https://www.ietf.org/rfc/rfc3339.txt, especially
> Appendix A) requires the "T." This spec adheres to ISO 8601, but is more
> restrictive. Most date/time libraries can handle this fine.
>
good to know, but I don't know if there's any way to know how well
supported it is across the board in CF readers :-(
-CHB
> Cordially,
> Aaron
>
> On Thu, Sep 22, 2016 at 2:54 PM, <cf-metadata-request at cgd.ucar.edu> wrote:
>
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>> Today's Topics:
>>
>> 1. Re: Temporal nitpicks. Was: CF-metadata Digest, Vol 161,
>> Issue 3 (Chris Barker)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Thu, 22 Sep 2016 13:54:04 -0700
>> From: Chris Barker <chris.barker at noaa.gov>
>> To: Jim Biard <jbiard at cicsnc.org>
>> Cc: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
>> Subject: Re: [CF-metadata] Temporal nitpicks. Was: CF-metadata Digest,
>> Vol 161, Issue 3
>> Message-ID:
>> <CALGmxEJoWkZ=-_AwA-d=AH-x9t1o+u9AgaMHtMKSXRkaaEpgwg at mail.
>> gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> On Thu, Sep 22, 2016 at 12:06 PM, Jim Biard <jbiard at cicsnc.org> wrote:
>>
>> > 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).
>> >
>> >
>> Thanks! so UDUNITS is quite flexible -- make this easier :-)
>>
>> > 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.
>> >
>> Isn't the "classical" form ISO8601 without the "T" ?
>>
>> > Software written to that form could very well break if a different form
>> is
>> > used.
>> >
>> well, the spec says UDUnits, so it's up to the software to fix itself :-)
>> IN any case, I know I"ve seen files that claim to be CF compliant both
>> with
>> and without the "T" -- and, in fact, we had to update the python lib a
>> couple years ago to accommodate the "T". But if we are sure that the no T
>> version is the most common, then whe can make that the official
>> recommendation -- it does seem to be ISO compliant a swell.
>>
>> 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.
>> >
>> yeah, that's a mess, but a distinct issue, yes?
>>
>> 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 is in the docs now:
>>
>> *Note: if the time zone is omitted the default is UTC, and if both time
>> and
>> time zone are omitted the default is 00:00:00 UTC.*
>>
>> Which is unfortunate. But it's been there "forever", yes? It does mean
>> that
>> there is no way in CF to specify local time, but that may be a good thing.
>> "local time" is a really poorly defined concept. I don't have the official
>> ISO docs, but the wikipedia page doesn't define it.
>>
>> In other contexts (at least the Python datetime world) the concept "naive
>> time" is used. what this means is that you have no idea what time zone it
>> is, but it behaves as UTC (i.e. no DST). It's up to the app to know what
>> time zone it is dealing with. I think that's what an ISO8601 string with
>> no
>> offset really is.
>>
>> But CF says it's UTC, so it's UTC.
>>
>> But we don't have to actually recommend that anyone use that, or show it
>> in
>> any examples.
>>
>> Are we converging on ISO8601 without the "T", and always with an offset or
>> "Z" as the recommended way to express datetimes in CF?
>>
>> -CHB
>>
>>
>>
>>
>> > 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>
>> > 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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>> >
>> > --
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>> > Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
>> > *Research Scholar*
>> > Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/
>> >
>> > North Carolina State University <http://ncsu.edu/>
>> > NOAA National Centers for Environmental Information
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>> --
>>
>> Christopher Barker, Ph.D.
>> Oceanographer
>>
>> Emergency Response Division
>> NOAA/NOS/OR&R (206) 526-6959 voice
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>> Seattle, WA 98115 (206) 526-6317 main reception
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>
>
>
> --
> Aaron D. Sweeney, Ph. D.
> Water Level Data Manager
>
> Cooperative Institute for Research in Environmental Sciences (CIRES)
> University of Colorado at Boulder
> and
> NOAA National Centers for Environmental Information
> *formerly NOAA's National Geophysical Data Center*
> 325 Broadway, E/NE42
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> Phone: 303-497-4797, Fax: 303-497-6513
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--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
Chris.Barker at noaa.gov
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Received on Fri Sep 23 2016 - 13:06:26 BST
