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...
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
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Received on Fri Nov 02 2007 - 08:30:51 GMT
