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>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] On Behalf Of Steve Emmerson
> Sent: 18 March 2011 17:14
> To: 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
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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