NetCDF
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NetCDF (Network Common Data Form) is a machine-independent, self-describing, binary data format standard for exchanging scientific data. The project homepage is hosted by the University Corporation for Atmospheric Research (UCAR). They are also the chief source of netCDF software, standards development, updates etc. The format is an open standard.
The project is actively supported, currently at version 3, and with plans underway for a version 4. It is planned to merge the project in version 4 with the HDF5 data file format, giving an alternative netCDF interface to HDF5 files.
The format was based on conceptual model of the NASA CDF but is not compatible with it.
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Format description
The data is kept in a "self-describing" format. This means that there is a header describing the various data arrays that are upcoming, which allows you to mention things like their length, stored format (i.e. int16, int32 etc), some free text metadata, a few other things. The format is defined platform independently, with issues such as endianness being addressed in the software libraries.
Software
Access libraries
The software libraries supplied by UCAR provide read-write access to netCDF files, encoding and decoding the necessary arrays and metadata. The libraries themselves are written in C, but provide an API for C, [[C++]] and Fortran code. A Java interface is also available from UCAR. Interfaces to netCDF are also available in other languages including R (ncdf and ncvar packages), Perl, Python, Ruby, and IDL. The specification of the API calls is very similar across the different languages, apart from inevitable differences of syntax. The API calls for version 2 were rather different from those in version 3, but are also supported by version 3 for backward compatibility. Application programmers using supported languages need not normally be concerned with the file structure itself, even though it is available as an open format.
Applications
A wide range of application software has been written which makes use of netCDF files. These range from command line utilities to graphical visualisation packages.
- A commonly used set of Unix command line utilities for netCDF files is the NetCDF Operators (NCO) suite, which provide a range of commands for manipulation and analysis of netCDF files including basic record concatenating, slicing and averaging.
- NcBrowse is a generic netCDF file viewer that includes Java graphics, animations and 3D visualizations for a wide range of netCDF file conventions.
- NCAR Command Language is used to display and process data in netCDF files (among other formats).
Common uses
It is commonly used in climatology applications (e.g., weather forecasting, climate change) and GIS applications.
It is an input/output format for many GIS applications, and for general scientific data exchange. To quote from their site "NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netCDF library also defines a machine-independent format for representing scientific data."
See also
- Common Data Format (CDF)
- GRIB (GRIdded Binary)
- Hierarchical Data Format (HDF)
- FITS
External links
- netCDF project page at the University Corporation for Atmospheric Research
- netCDF4 project page
- ncBrowse - generic netCDF file viewer - includes Java graphics, animations and 3D visualizations for wide range of netCDF file conventions
- "An Introduction to Distributed Visualization"; section 4.2 contains a comparison of CDF, HDF, and netCDF.
- NCO a suite of programs known as operators, which facilitate manipulation and analysis of netCDF files
- This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.