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 <[email protected]
<mailto:[email protected]>> 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: [email protected]
<mailto:[email protected]>
[mailto:[email protected]
<mailto:[email protected]>] On Behalf Of Steve Emmerson
Sent: 18 March 2011 17:14
To: [email protected] <mailto:[email protected]>
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 [email protected]
<mailto:[email protected]>
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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