[netcdf-java] Date precision while aggregating data

[Bob Simons]

While one can debate whether the netCDF libraries should round (not 
truncate) date/time values stored as doubles to the nearest millisecond 
(I think they should), or whether it's a bug in Java (I think not - Java 
does date/time calculations with longs), it doesn't solve the immediate 
problem of storing date/time values in netCDF files for use with the 
current netCDF libraries.

I think there is a simple solution: store date/time values with units 
that allow all of the date/time values to be expressed as integer values 
(in the mathematical sense). In practice, the values often will need to 
be calculated as Java longs and stored as Java doubles in netCDF files 
to gain extra precision, since there is no support for longs in netCDF 
files.

For example, use "seconds since 1970-01-01T00:00:00Z" if your dates/time 
data is measure to the nearest second.  Or, use milliseconds, minutes, 
hours, or days, ... as appropriate.  Even when millisecond values are 
stored as doubles and even if the "since" time is in the 1800's, there 
should be no round-off error and Java and netCDF-java should calculate 
the dates/times correctly.


Sincerely,

Bob Simons
Satellite Data Product Manager
Environmental Research Division
NOAA Southwest Fisheries Science Center
1352 Lighthouse Ave
Pacific Grove, CA 93950-2079
(831)658-3205
bob.simons at noaa.gov

The contents of this message are mine personally and
do not necessarily reflect any position of the
Government or the National Oceanic and Atmospheric
Administration.
<>< <>< <>< <>< <>< <>< <>< <>< <><