netCDF

The development of the netCDF interface began within the Unidata Program Center in Boulder, Colorado. The goal was to provide a common interface between Unidata applications and ingested real-time meteorological data. Since Unidata's software was intended to run on multiple hardware platforms with access from both C and FORTRAN, achieving Unidata's goals had the potential for providing a package that was useful in a broader context. By making the package widely available and collaborating with other organizations with similar needs, Unidata hoped to encourage reuse of scientific software within and across disciplines.

Important concepts employed in the netCDF software originated in a paper that described data-access software developed at the NASA Goddard National Space Science Data Center (NSSDC). The interface provided by this software was called the Common Data Format (CDF), originally a platform-specific FORTRAN library to support an abstraction for storing multidimensional scientific data.

An extensive collection of applications had used the NASA CDF package for many different kinds of data. It had the virtues of simplicity (only 13 subroutines), independence from storage format, generality, ability to support logical user views of data, and support for generic applications. In 1988, Unidata worked with Dave Raymond (of the New Mexico Institute of Mining and Technology) using some of his ideas to come up with the first netCDF software interface.

NetCDF is an interface for array-oriented data access and a freely distributed collection of software libraries for C, Fortran, C++, Java, and perl that implement the interface. The netCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. These deal with a variety of data types that encompass data such as single-point observations, time series, regularly spaced grids, and satellite or radar images. Since netCDF is an interface and library, the user is unaware of the format within.

A netCDF dataset is stored as a single file comprising two parts: A header containing all the information about dimensions, attributes, and variables except for the variable data; A data part comprising fixed-size data, containing the data for variables that don't have an unlimited dimension and variable-size data, containing the data for variables that have an unlimited dimension.

Both the header and data parts are represented in a machine-independent form. This form is very similar to XDR (eXternal Data Representation), extended to support efficient storage of arrays of non-byte data.

The components of a netCDF file are its dimensions, variables, and attributes. These components can be used together to capture the meaning of data and relations among data fields in a scientific data set.

There are six primitive netCDF data types: byte (eight bits), character (eight bits), short integer (16 bits), long integer (32 bits), floating-point (32 bits), or double-precision floating-point (64 bits).

The netCDF homepage

The netCFD specification