A major conceptual difference between these two approaches is that
znetcdf defines a new filetype, whereas HDF files containing compressed
objects are still defined as HDF.
A "compressed variable" approach could be applied to NetCDF, thus avoiding
a new *DF type. Perhaps the relevant compression parameters could be stored
as attributes, such as 'compressed = "true";' and 'compression_factor = 5;'.
Global atts could hold default parameters, while variable atts would hold
settings for individual variables.
Just a thought,
Bill Weibel (Not the original Bill)
P.S. At least twice now, I've seen the NetCDF magic string referred to as
"CDF1"*, yet in the actual files, the value is "CDF\001".
Does anyone know how this inconsistency got going?
*"Graphics File Formats" by Brown and Sheperd, p 400.
On Apr 9, 12:17pm, Arlindo da Silva wrote:
> Subject: Re: Compressed netCDF library available
> Bill,
>
> >
> > Arlindo -- I haven't looked at their library. Do you have a link
> > to it? --Bill
> >
> > > If I am not mistaken, this is precisely what MFHDF (NCSA's NetCDF API
> > > for HDF) does thru an interface to zlib. Have you compared your
> > > approach with theirs? I makes me a little worried to have yet another
> > > *DF format around.
> >
>
> The HDF home page is:
>
> http://hdf.ncsa.uiuc.edu/
>
> For information on data compression look at the FAQ:
>
> http://hdf.ncsa.uiuc.edu/HDF-FAQ.html#18
>
>
> Quoting:
>
> 18) Does HDF support data compression?
>
> HDF 4.0 (and later releases) supports a low-level compression
> interface, which allows any data-object to be
> compressed using a variety of algorithms.
>
> Currently only three compression algorithms are supported: Run-Length
> Encoding (RLE), adaptive Huffman, and an
> LZ-77 dictionary coder (the gzip 'deflation' algorithm). Plans for
> future algorithms include an Lempel/Ziv-78 dictionary
> coding, an arithmetic coder and a faster Huffman algorithm.
>
> HDF 4.0 (and later releases) supports n-bit compression for SDSs.
>
> HDF 4.0 (and later releases) supports RLE (Run Length Encoding),
> IMCOMP, and JPEG compression for raster images.
>
> New with HDF 4.1 is support for "chunking" and "chunking with
> compression". Data chunking allows an n-dimensional
> SDS or GR image to be stored as a series of n-dimensional chunks. See
> the HDF User's Guide for more information.
>
>
> --
> Arlindo da Silva
> dasilva@xxxxxxxxxxxxx
>-- End of excerpt from Arlindo da Silva
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William Weibel weibel@xxxxxxxxxxxxxxxxxx
Jet Propulsion Laboratory Tel. (818)354-0728 \\\\/
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William Weibel weibel@xxxxxxxxxxxxxxxxxx
Jet Propulsion Laboratory Tel. (818)354-0728 \\\\/
4800 Oak Grove Dr. MS 183-501 4-1812 O-O
Pasadena, CA 91109-8099 Fax (818)393-5103 |
U.S.A. -
||||DISCLAIMER: Neither JPL nor I speak for each other. | | | | | | | ||||
