[netcdfgroup] Ann: NCL/PyNIO now have support for netCDF-4 classic format (fwd)

[David Brown]

Hi Ed,

Yes we realize that NetCDF 4 allows per variable decisions about  
compression,
but we are guessing that most NCL and PyNIO users will be happy just  
to compress
everything in the file. Again this is in the interest of keeping  
things simple.

If and when someone comes up with a use case where individual  
decisions about the
compression of each variable are important, we will be happy to  
revisit this currently
missing capability.
  -dave

---------- Forwarded message ----------
Date: Mon, 27 Aug 2007 10:38:17 -0600
From: Ed Hartnett <ed at unidata.ucar.edu>
To: Jeff Whitaker <jswhit at fastmail.fm>
Cc: Mary Haley <haley at ucar.edu>, netcdfgroup at unidata.ucar.edu
Subject: Re: [netcdfgroup] Ann: NCL/PyNIO now have support for  
netCDF-4 classic
     format
B
Jeff Whitaker <jswhit at fastmail.fm> writes:

> Mary Haley wrote:
>> Hi all,
>>
>> This is a bit of a late announcement, but NCL V4.3.1 and PyNIO V1.2.0
>> have support built-in for reading and writing netCDF-4 classic files
>> on systems where netcdf-4.0-beta1 is supported.
>>
>> With NCL, you can write a netCDF-4 classic file by calling the
>> "setfileoption" procedure with the "format" option before you call
>> "addfile" to create a netCDF-4 classic 4 file:
>>
>>    setfileoption("nc","format","netcdf4classic")
>>    a = addfile("file.nc","c")
>>
>> You can further specify a compression level:
>>
>>    setfileoption("nc","compressionlevel",5)
>>
>> Similar code exists for PyNIO:
>>
>> import Nio
>> opt                  = Nio.options()
>> opt.Format           = "netcdf4classic"
>> opt.CompressionLevel = 5
>>
>> fout = Nio.open_file("file.nc","c",opt)
>>
>> For more information, see the NCL "setfileoption" or PyNIO  
>> documentation:
>>
>>    http://www.ncl.ucar.edu/Document/Functions/Built-in/ 
>> setfileoption.shtml
>>    http://www.pyngl.ucar.edu/Nio.shtml
>>
>> For download:
>>
>>     http://www.ncl.ucar.edu/Download/
>>     http://www.pyngl.ucar.edu/download.shtml
>>
>> Cheers,
>>
>> --Mary
>>
>>
>
> Mary:  Can you turn the shuffle filter on with setfileoption?  I've
> found that it can really improve the compression ratios when used in
> conjunction with zlib compression in netcdf-4 files.
>
> -Jeff
>

Howdy Mary and Jeff!

Just wanted to point out that compression is a per-variable feature,
not a per-file feature.

That is, different variables in the file can have different
compression factors (or none at all).

Thanks!

Ed

-- 
Ed Hartnett  -- ed at unidata.ucar.edu