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

Hi Jeff,

Currently NCL and PyNIO turn on the shuffle filter whenever compression is requested. My reading of the docs suggested that there were no disadvantages to having shuffle set on all the time, and so I did not make it an option in the interest of keeping things simple.

So is this okay as far as you (or anyone else with knowledge of these things) are concerned, or do I need to make this something the user controls? It would be easy enough to make it optional,
 -dave


On Aug 27, 2007, at 9:39 AM, Jeff Whitaker wrote:

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

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