NetCDF

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NetCDF

General description

The Network Common Data Form (netCDF) is a long-lived set of file formats and associated APIs designed by UCAR for multi-dimensional datasets. (Though its name resembles that of CDF, and their original designs were similar, the two products have greatly diverged.) The various versions are widely used in environmental science, especially atmospheric and oceanographic research. Currently it has two main versions, netCDF-3 and netCDF-4, which are quite different in implementation, and moderately different in API. There are also "subversions" of netCDF-3, notably "netCDF Classic." Tool support for netCDF-3 continues to exceed that for netCDF-4; but the latter, based on HDF5, is generally considered technically superior, so its tool support is increasing rapidly.

Notable features of netCDF include

• incorporation of metadata. netCDF is said to be "self-describing," in that the file format provides for a header describing the structure of the data. In practice, the utility of its metadata depends on the extent to which the data author provides and maintains it.
• platform independence via API: provided the user manipulates netCDF files via supported APIs (which are numerous), the user can effectively ignore issues such as endianness.
• backward compatibility. Software and API capable of manipulating netCDF-4 is also capable of manipulating netCDF-3, though of course advanced features of the later version are not accessible to files written for the earlier version.

There are 4 main versions of NetCDF:

• the classic format
• the 64-bit offset format
• the netCDF-4 format
• the netCDF-4 classic model format

Either of the first two may be referred to as NetCDF-3.

NetCDF is described on the Unidata pages of the UCAR web site. A short document describing early versions has been accepted as a standard by NASA.

Other information

The format is referenced in the Wikipedia page on NetCDF.

NetCDF claims full backwards compatibility.

Software and information is made available according to UCAR Terms of Use, which indicate they are freely usable for non-commercial purposes.

Software

There is a wide range of software available to create and process NetCDF files. The Wikipedia article mentioned above as a good starter list.

Sample files

Sample NetCDF files are available on the Unidata web site.

Identification

The magic number is CDF\001 .

The file extension is .nc (originally .cdf) and the MIME Type is application/netcdf or application/x-netcdf.

References

The User's Guide is: Rew, R. K., G. P. Davis, S. Emmerson, and H. Davies, NetCDF User's Guide for C, An Interface for Data Access, Version 3, April 1997.