[netcdfgroup] NetCDF 4 and ncgen

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: [netcdfgroup] NetCDF 4 and ncgen
• From: Don Hooper <hoop@xxxxxxxxxxxx>
• Date: Wed, 7 May 2008 12:57:45 -0600 (MDT)

All,

The way we here go about creating so many NetCDF files is a process that I
like to call "templating".  We create a CDL that has the coordinate variables'
data, except for "time".  There is no data in the CDL for the data variable
or for time.  We then run ncgen on the CDL, and then that "template" NetCDF
file is "populated" by a program (usually C, but not necessarily).  All the
program has to do is write out grids to the data variable, add a value to
the time coordinate vector, and update the actual_range attribute of both
variables.  A simpler program is easier to get right than one that has
to create all the dimensions, variables, and attributes, as I'm sure all
would agree.  ;)

What occurs to me is the complication that NetCDF-4 introduces.  I'm told
that, to take advantage of any compression mechanism in the NetCDF-4 file,
this must be set on file creation.  Well, we create the files with ncgen.  So,
unless ncgen (or CDL) is enhanced to specify this compression mechanism, we
will lose out.  So I hope that such an enhancement will be considered for
ncgen/CDL with regard to NetCDF-4.

Thanks,
-Hoop