NetCDF is a great, portable data format but the resulting files are _not_
small. This has lead many groups to try different ways to reduce the file
size that complicates netCDFs simple data access methods (scale and
offsets, data masks).
Others just gzip up the data files and uncompress them when necessary. This
usually yeilds a 70-90% reduction in file size but makes makes access
cumbersome, especially if you are reading large files off cdroms.
It would be nice to access these compressed files directly.
I have written a set of modifications to the netCDF library source that
allow exactly that.
This makes a drop in replacement that will allow transparent access to
both compressed and uncompressed netCDF files. You just have to relink
against the znetcdf library. Creating compressed netCDF files requires
a small change to the flags in the nccreate routine.
There is a page with a more complete explanation, the source changes,
instructions on how to patch the netcdf-3.3.1 source, and some perfomance
numbers:
http://snow.cit.cornell.edu/noon/z_netcdf.html
This has been used on the following platforms with not problems:
dUNIX, MacOS, linux, IRIX, Solaris, AIX, openstep, Rhapsody.
If folks want, and contribute, I will collect precompiled libraries on
this link as well.
Try it out and send me your comments.
--Bill Noon
Northeast Regional Climate Center
Cornell University
