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[netCDF #CDI-919203]: compression question

Hi Arlyn,
 
> I have netcdf files written using utilities in R and python.  I am
> trying to figure out whether the files were written with internal
> compression (i.e. I want to know if I can rewrite them and make them
> smaller).  I can do some tests to figure this out, but I wonder if there
> is a utility that returns file format and compression information? I did
> get format information from 'ncdump -k' but cannot find anything about
> compression.

Yes, if you want to know compression information about "file.nc", you can
use the "-s" option of ncdump ("-s" stands for "special virtual attributes"):

  ncdump -s -h file.nc

The "-h" option prints only header information, so you don't get a complete 
data dump. See the ncdump man page for the meanings of the special virtual 
attributes:

  http://www.unidata.ucar.edu/netcdf/docs/ncdump-man-1.html

You want to look at is '_DeflateLevel', which, if present, means the variable 
has been compressed (at some level from 1 to 9).

If your files are not compressed the easiest way to see how much they can be
compressed is using the nccopy utility:
 
  http://www.unidata.ucar.edu/netcdf/docs/nccopy-man-1.html

--Russ
Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: CDI-919203
Department: Support netCDF
Priority: Normal
Status: Closed