On Aug 19, 2011, at 7:54 AM, Jon Blower wrote:
> Hi Chris,
>
> Does the calendar system usually define whether leap-seconds are taken into account or not?
Generally speaking, I don't believe so, if only because calendar systems usually go down to the day granularity. Seconds-based doordinate time standards, such as UTC and TAI do, because they have to. Julian date (NOT the day of year many associate with the name) is an exception, with its fractional dates.
> In other words, given knowledge of which calendar system is in use, could a library make the correct calculation? Or is other information needed too?
Actually, it may be more a matter of what the user/application wants as output.
Alas, I'm afraid I am not enough of an expert on coordinate time standards, as they are exceedingly complex, almost byzantine. See such items on Wikipedia as:
http://en.wikipedia.org/wiki/Terrestrial_Time,
http://en.wikipedia.org/wiki/Universal_Time and
http://en.wikipedia.org/wiki/International_Atomic_Time,
http://en.wikipedia.org/wiki/Julian_Date, ...
>
> Presumably this would only affect real-world calendars, and perhaps only UTC?
>
> Cheers, Jon
>
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Lynnes, Christopher S. (GSFC-6102)
> Sent: 19 August 2011 12:46
> To: John Caron
> Cc: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] CDM calendar date handling
>
> On Aug 18, 2011, at 6:23 PM, "John Caron" <caron at unidata.ucar.edu> wrote:
>
>>> In order to do calculations
>>> with times, which are often necessary, we need to be able to convert
>>> them into a form which has a fixed-length unit since a reference time
>>> (like udunits), even though that isn't the most convenient way to express them.
>> I think that given two calendar dates in the same calendar, there will
>> be a well-defined # seconds between them.
>
> Yes...and no. There is the question of leap seconds. In the satellite data world, most people account for them, but not everyone. Some (most?) off the shelf packages do not.
> --
> Chris Lynnes
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--
Dr. Christopher Lynnes NASA/GSFC, Code 610.2 phone: 301-614-5185
Received on Fri Aug 19 2011 - 07:48:55 BST
