On 30.10.2010 01:35, John Caron wrote:
> 1) no one is suggesting to replace the udunits convention; the
> original suggestion a few years back was to allow ISO 8601
> formatted time strings in addition.
>
> 2) Udunits accepts ISO Strings for the date part, AFAIU, but
> allows more variations I think.
Yes, or at least this would be a good principle to follow. Alas, Udunits
lacks a bit to fully accept any ISO 8601 timestamp, even if only the
date part is considered. For example, a date like "20101101" is accepted
neither as DATE nor as TIMSTAMP (sic) according to the referenced
Udunits-2 unit grammar, AFAICT.
I suppose this is also a question of amending the Udunits library itself
so that full ISO 8601 compliance is achieved. This is something that
would also make it more suitable in a number of other applications
besides the netCDF-related ones, I suppose.
> The formal grammar is here:
>
> http://www.unidata.ucar.edu/software/udunits/udunits-2/udunits2lib.html#Grammar
Thanks for the link!
(I was aware of it, but wasn't sure whether it applied to Udunits-2
only, or just Udunits in general...)
> 3) The problem with udunits time handling is that it doesnt handle
> anything other than the default Calendar. So, it cant be used as the
> reference implementation for non-standard Calendars.
I believe the same "problem" exists with ISO 8601 as well.
I also think that adding calendar support is an issue that should be
introduced with great caution. Calendars are location and culture
specific, and even when dealing with historical or culture-specific
dates (how applicable is that to CF?) one needs quite a bit of
additional meta information to clearly deal with such a "calendar time
scale".
For scientific usage, I would claim that while any such time scale can
definitely be useful, one would still sooner or later need to convert
that "time unit" into something that can be related to _other_ time
scales, at least if sharing and reuse of data is a concern (which it
should, IMHO!). To me, it seems that the only internationally accepted
common standard, or de facto "reference time scale", is the current
Gregorian calendar. It is often used in parallel with other calendars.
If data in _other_ calendars (i.e. "time scales") were to be specifiable
in CF, then at least some means of unambiguously mapping them to
"Gregorian ISO 8601" would need to be settled.
--
Regards,
-+-Ben-+-
Opinions expressed are my own, not necessarily those of my employer.
Received on Mon Nov 01 2010 - 11:36:20 GMT
