hmm, where do you see that part about "the iso8601 string implies a
moment and a width a.k.a resolution". i was reading it that the duration
= width spec was separate.
in any case, this probably highlights the need to be specific about what
CF semantics are.
On 3/18/2011 12:27 PM, Benno Blumenthal wrote:
> It is worse than that -- though the local time of the standard creates
> a problem for us -- according to the iso standard, if time is omitted,
> the string corresponds to the whole day, not the start of the day --
> ISO8601 is a time *interval* standard -- the iso8601 string implies a
> moment and a width a.k.a resolution. For example, 2001-01-01/07 is
> the first week of 2001 is an ISO8601 string. This is an "excellent"
> time representation, and an essential characteristic of a good time
> representation, but does not map well into software that only holds an
> instantaneous time, or even XML Schema for that matter. CF, of
> course, has bounds, so that the edges of the time interval can be
> specified.
>
> Benno
>
> On Fri, Mar 18, 2011 at 1:23 PM, Jon Blower <j.d.blower at reading.ac.uk
> <mailto:j.d.blower at reading.ac.uk>> wrote:
>
> > Just so you know, the UDUNITS package does assume the first day
> of the
> > year at 00:00:00 UTC if additional resolution time-fields are
> omitted.
> > This conforms to the ISO standard.
>
> Actually (according to Wikipedia at least) the ISO8601 standard
> assumes local time if the time zone is omitted. I'm not sure what
> time information (if any) is inferred if the ISO string omits
> hours/minutes/seconds (i.e. I don't think 2008-01-01 is inferred
> to be the same as 2008-01-01T00:00:00Z).
>
> But it's important to highlight that UDUNITS does assume midnight
> UTC if no time is provided. It implies that the temporal
> resolution is not to be inferred from the length of the UDUNITS
> time string.
>
> Jon
>
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>
> [mailto:cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>] On Behalf Of Steve Emmerson
> Sent: 18 March 2011 17:14
> To: cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] udunits handling of fuzzy time units
>
> Martin,
>
> On 03/18/2011 04:11 AM, Schultz, Martin wrote:
> > PS: I do disagree with Christopher when he says ''"30 days since
> 31 Jan 2008" is perfectly well defined.'' - do you refer to 00 UTC
> or 12 UTC on 31 Jan 2008? Or even 00:00 UTC or 01:02:30.3625132 h
> UTC? OK: if you define an "oceanographic calendar" (where anything
> shorter than a day doesn't matter), you could have a rule that all
> hours, minutes, seconds, milliseconds, etc. are mapped onto one
> value (say 00:00:00 h UTC). But you will need to define this rule
> in order to give a meaning to your calendar.
>
> Just so you know, the UDUNITS package does assume the first day of the
> year at 00:00:00 UTC if additional resolution time-fields are omitted.
> This conforms to the ISO standard.
>
> Regards,
> Steve Emmerson
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>
>
>
> --
> Dr. M. Benno Blumenthal benno at iri.columbia.edu
> <mailto:benno at iri.columbia.edu>
> International Research Institute for climate and society
> The Earth Institute at Columbia University
> Lamont Campus, Palisades NY 10964-8000 (845) 680-4450
>
>
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