David Stuebe writes:
> I support Rich and Balaji in creating a two integer time standard. I think
> the tick_length as a attribute is a great idea for non-rational times, and I
> agree with Rich that the major unit should be specified by the user - Days,
> Second, Hours, Years etc...
I would still prefer if the major unit were not calendar- (or planet-:-)
specific -- seconds, minutes and hours are universal constants and
should be the only ones allowed -- but hey, I'll go with the flow.
Just to be clear: the 'tick' allows you to be precise about fractions
of time units, but not 'non-rational' times: 1/3 second is rational. To
be equally clear, all floating-point numbers are rational, so I don't
think this is an issue. If you really need a model with a timestep of
'pi' seconds, I think you have a problem anyway, with or without CF...
>
> Concerning Days and earth-centric time units in UDUNITS
>
> Days - or rather (Modified) Julian Date as defined using a two integer time
> variables is an extremely practical method of storing time information for
> many, but not all applications. A standard for time and date which includes
> the needed definition of Day and time origin is important, (leap seconds
> aside) although not general as you pointed out for ET models... A definition
> of Day should remain in UDUNITS. Is there a standard for setting time origin
> for MJD and JD?
>
> I found it difficult to set time origin using an attribute, the string gets
> complicated. I would suggest a seperate variable if it does not conform to
> some recognized standard like JD or MJD...
>
> About the choice of Millisecond as the minor unit, it is not arbitrary for
> storing MJD dates, there are more Microseconds in a day than can be stored
> in a 32-bit integer. To avoid dealing with long integers, I choose
> Milliseconds for FVCOM output, though in the model, the Time Type/Class uses
> 64-bit integers and microseconds.
>
> I don't see a type name for 64-bit integers in the NETCDF 3 docs - am I
> missing something?
>
> David
>
--
V. Balaji Office: +1-609-452-6516
Head, Modeling Systems Group, GFDL Home: +1-212-253-6662
Princeton University Email: v.balaji at noaa.gov
Received on Fri Nov 02 2007 - 08:58:56 GMT
