This chapter contains answers to some of the most frequently asked questions about netCDF. A more comprehensive and up-to-date FAQ document for netCDF is maintained at
`http://www.unidata.ucar.edu/packages/netcdf/faq.html'
NetCDF (network Common Data Form) is an interface for array-oriented data access and a freely-distributed collection of software libraries for C, FORTRAN, C++, and perl that provide implementations of the interface. The netCDF software was developed by Glenn Davis, Russ Rew, and Steve Emmerson at the Unidata Program Center in Boulder, Colorado, and augmented by contributions from other netCDF users. The netCDF libraries define a machine-independent format for representing arrays. Together, the interface, libraries, and format support the creation, access, and sharing of arrays.
NetCDF data is:
Source distributions are available via anonymous FTP from the directory
`ftp.unidata.ucar.edu:pub/netcdf/'
Files in that directory include:
netcdf.tar.Z
netcdf-beta.tar.Z
Binary distributions for some platforms are available from the directory
`ftp://ftp.unidata.ucar.edu/pub/binary/'
Source for the perl interface is available as a separate package, via anonymous FTP from the directory
`ftp://ftp.unidata.ucar.edu/pub/netcdf-perl/'
Yes, the latest version of this FAQ document as well as a hypertext version of the NetCDF User's Guide and other information about netCDF are available from
`http://www.unidata.ucar.edu/packages/netcdf'
Version 2.4 incorporates support for new platforms and updated versions of previously-supported platforms, provides new optimizations for Cray/UNICOS, incorporates fixes for reported bugs, improves the documentation, and improves ease of installation. For more details, see
`http://www.unidata.ucar.edu/packages/netcdf/release-notes.html'
Yes.
For information about the mailing list
and how to subscribe or unsubscribe, send a message to
majordomo@unidata.ucar.edu
with no subject and with the
following line in the body of the message:
info netcdfgroup
The netCDF mailing list has almost 500 addresses (some of which are aliases to more addresses) in fifteen countries. Several groups have adopted netCDF as a standard way to represent some forms of array-oriented data, including groups in the atmospheric sciences, hydrology, oceanography, environmental modeling, geophysics, chromatography, mass spectrometry, and neuro-imaging.
A description of some of the projects and groups that have used netCDF is available from
`http://www.unidata.ucar.edu/packages/netcdf/usage.html'
See section NetCDF File Structure and Performance, for an explanation of the physical structure of netCDF data at a high enough level to make clear the performance implications of different data organizations. See section File Format Specification, for a detailed specification of the file format.
Programs that access netCDF data should perform all access through the documented interfaces, rather than relying on the physical format of netCDF data. That way, any future changes to the format will not require changes to programs, since any such changes will be accompanied by changes in the library to support both the old and new versions of the format.
The current version of netCDF has been tested successfully on the following platforms:
Utilities available in the current netCDF distribution from Unidata are
ncdump
, for converting netCDF files to an ASCII human-readable
form, and ncgen
for converting from the ASCII human-readable form
back to a binary netCDF file or a C or FORTRAN program for generating
the netCDF file.
Several commercial and freely available analysis and data visualization packages have been adapted to access netCDF data. More information about these packages and other software that can be used to manipulate or display netCDF data is available from
`http://www.unidata.ucar.edu/packages/netcdf/software.html'
The Scientific Data Format Information FAQ, available from
`http://fits.cv.nrao.edu/traffic/scidataformats/faq.html'
, provides a good description of other access interfaces and formats for array-oriented data, including CDF and HDF.The default error handling behavior of all the netCDF functions is to exit on error, but this behavior is under programmer control. You can independently control the fatality of errors and the appearance of messages from errors detected in netCDF library calls. See section Error Handling, for more information.
If you find a bug, send a description to support@unidata.ucar.edu
.
This is also the address to use for questions or discussions about
netCDF that are not appropriate for the entire netcdfgroup
mailing list.
A search form is available at the bottom of the netCDF home page providing a full-text search of the support questions and answers about netCDF provided by Unidata support staff.
It provides all the functionality of the C interface (except for the
subsampled or mapped array access of ncvarputg
and
ncvargetg
), improves type safety by eliminating use of void*
pointers, and is somewhat simpler to use than the C interface. With the
C++ interface,
no IDs are needed for netCDF components, there is no need
to specify types when creating attributes, and less indirection is
required for dealing with dimensions. However, the C++ interface is
less mature and less-widely used than the C interface, and the
documentation for the C++ interface is less extensive, assuming a
familiarity with the netCDF data model and the C interface.
It provides all the functionality of the C interface. The FORTRAN interface uses FORTRAN conventions for array indices, subscript order, and strings. There is no difference in the on-disk format for data written from the different language interfaces. Data written by a C language program may be read from a FORTRAN program and vice-versa.
It provides all the functionality of the C interface. The Perl interface uses Perl conventions for arrays and strings. There is no difference in the on-disk format for data written from the different language interfaces. Data written by a C language program may be read from a Perl program and vice-versa.
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