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Re: 980521: kalyani

>To: address@hidden
>From: "Dr . Kalyani " <address@hidden>
>Subject: kalyani
>Organization: .
>Keywords: 199805211036.EAA14515

Hi Dr. Kalyani,

>        I have few doubts about netcdf usage can you help me in solving
> the following problems
> 
> 1. I want to append 3 or 4 Netcdf files each file is of a size 220mb. is
> any specific command is available like ncegen and ncdump for appending
> netcdf files.

If you just want to package several different netCDF files together as
one file that can later be split up again, you can use the Unix "tar"
command.

If the files have a similar structure (same variables, dimensions,
attributes), you can create a single larger netCDF file that contains
all the data with one of the programs ncecat, ncks, or ncrcat from the
freely-available NCO (netCDF operators) package described at

  http://www.unidata.ucar.edu/packages/netcdf/software.html#NCO

Another utility that may be of use is nccat, Chuck Denham's program to
concatenate two netCDF files along their record dimension. The files
must be identical in variable names and dimensions. Each variable must
have a leftmost NC_UNLIMITED record dimension.  This program is part of
the User-Contributed netCDF software described and available from

  http://www.unidata.ucar.edu/packages/netcdf/contrib.html

under the entry "nccat.c".

> 2. can we compress netcdf files using any specfic command( i have
> compressed a file using gzip command,I am able to compress a file which is
> of size 220 mb to 107 mb, but I don't know whether it is of practise to
> compress files like that or not) if not why? 

Yes, you can compress netCDF files using gzip, but you will have to
uncompress a file before reading it.  The netCDF library can't read
netCDF files while they are still compressed.

If you need to be able to read files while they are compressed, Bill
Noon has written and made available a set of modifications to the netCDF
3.3.1 library source that allows transparent access to both compressed
and uncompressed netCDF files. You just have to relink against the
znetcdf library. Creating compressed netCDF files requires only one
additional flag in invoking the nccreate routine.

A more complete explanation, the source changes, instructions on how to
patch the netcdf-3.3.1 source, and some performance numbers are available
from

    http://snow.cit.cornell.edu/noon/z_netcdf.html 

--Russ

_____________________________________________________________________

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