Thanks Ed,
Could I request that the NetCDF documentation stated this clearly in the
INSTALL and the FAQ. Deciding whether to install SZIP is the first thing you
are asked to do when installing HDF5 and, as the NetCDF docs state, there are
licence implications. Therefore, it would be useful to know SZIP isn't
required for traditional NetCDF3 users looking to read/write NetCDF4.
Yours,
Stephen.
---
Stephen Pascoe +44 (0)1235 445980
British Atmospheric Data Centre
Rutherford Appleton Laboratory
-----Original Message-----
From: Ed Hartnett [mailto:ed@xxxxxxxxxxxxxxxx]
Sent: 07 September 2009 17:25
To: Pascoe, Stephen (STFC,RAL,SSTD)
Cc: netcdfgroup@xxxxxxxxxxxxxxxx
Subject: Re: [netcdfgroup] NetCDF4 format and SZIP
"Pascoe, Stephen (STFC,RAL,SSTD)" <stephen.pascoe@xxxxxxxxxx> writes:
> I'd like to clarify how using HDF5 with SZIP support affects the files
> created by the NetCDF4 library.
> Â
> According to the NetCDF4 INSTALL file you can optionally use HDF5+SZIP
> when building NetCDF4. This implies that either SZIP-compressed
> NetCDF4 is byte-compatible with ZIP-compressed NetCDF4 or that there
> are 2 incompatible compressed NetCDF4 formats (ZIP and SZIP). Can
> you confirm it is the former?
It's simple.
NetCDF-4 cannot create SZIP compressed HDF5 files.
But it is possible to read some HDF5 files with netCDF-4, even though they were
not created with netCDF-4. (This capability will expand with the 4.1 release,
which will read any HDF5 file that does not use references, circular group
structures, or a few other HDF5 features that are not supported in netCDF).
So the point of building HDF5 with SZIP is to allow these szip compressed files
to be read by netCDF-4. This is a read-only capability.
> Assuming it is the former, what is the advantage of using SZIP? Is
> SZIP automatically used if the HDF5 library has it?
> Â
> Thanks,
> Stephen.
> Â
Fans of szip say it gives better compression.
Thanks,
Ed
--
Ed Hartnett -- ed@xxxxxxxxxxxxxxxx
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