NetCDF (network Common Data Form)
with
CF (Climate and Forecast) Conventions

Minimalist version of a "profile" document
for implementors of OGC WCS clients or servers
using CF-netCDF Encoding Format.

Ben Domenico
Draft last modified: November 5, 2007

Brief Description

This section provides a concise overview of the netCDF binary encoding format using CF conventions.

NetCDF

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. Together, the interface, library, and format support the creation, access, and sharing of scientific data.

The netCDF software includes C, Fortran 77, Fortran 90, and C++ interfaces for accessing netCDF data. These libraries are available for many common computing platforms.

CF Conventions

The CF conventions define metadata that provide a definitive description of what the data in each variable represents, and of the spatial and temporal properties of the data. This enables users of data from different sources to decide which quantities are comparable, and facilitates building applications with powerful extraction, regridding, and display capabilities.

Documentation

This section provides pointers to documentation for netCDF and for the CF conventions. It contains explicit pointers to the key elements of the documentation that describe how the physical quantities represented in the dataset are named, how the location and time in space is specified -- the "what, where, when" of the datasets.

NetCDF

Home page:
http://www.unidata.ucar.edu/software/netcdf/

Documentation list:
http://www.unidata.ucar.edu/software/netcdf/docs/

Users Guide:
http://www.unidata.ucar.edu/software/netcdf/docs/netcdf.html

CF Conventions

CF Metadata Conventions General Web Page:
http://cf-pcmdi.llnl.gov/

CF Conventions Document:
http://cf-pcmdi.llnl.gov/documents/cf-conventions/

Standard names

What do the numbers in a netCDF dataset represent? e.g., temperature, pressure, wind speed, salinity, radiance, reflectivity

·         Description of CF standard names:
http://cf-pcmdi.llnl.gov/documents/cf-standard-names

·         Standard names table:
http://cf-pcmdi.llnl.gov/documents/cf-standard-names/6/cf-standard-name-table.html
http://cf-pcmdi.llnl.gov/documents/cf-standard-names/6/cf-standard-name-table.xml

Units

What are the units of measure for the numbers in a netCDF dataset?

·         Description of CF units of measure:
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.0/ch03.html#units

·         Units table:
http://www.unidata.ucar.edu/software/udunits/udunits-1/udunits.txt

Coordinate types

Where in space do the numbers represent measurements or modeled values?

·         Coordinate types description:
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.0/ch04.html

Coordinate systems

·         Coordinate systems description:
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.0/ch05.html

Time coordinate

When were the measurements taken or modeled values forecast?

·         Time coordinate description:
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.0/ch04s04.html

Code for Implementing netCDF Interface

This is simply a pointer to a page where one can access computer code for implementing the netCDF interface.

netCDF libraries are available for download at:
http://www.unidata.ucar.edu/software/netcdf/

Support

Potential users of netCDF may be interested in what support is available for the code and interface.

Pointers to FAQ, mailing lists, etc.:
http://www.unidata.ucar.edu/software/netcdf/

CF-netCDF and Coverage (ISO 19123) Data Model Mapping

For use in the context of WCS, it is important to have an understanding of the mapping between the data models used for OGC coverages and those for the netCDF with CF conventions. At this time, there are two documents that describe this mapping -- in vastly different detail.

Limitations

The document below lists limitations and known issues relating to the use of netCDF encoding format in WCS.

CF-netCDF WCS Limitations and Known Issues
http://www.unidata.ucar.edu/projects/THREDDS/GALEON/CF-netCDF-WCSlimitations.htm

NetCDF Examples

A set of representative examples of netCDF datasets is essential for gaining an understanding. A good place to start is:

http://www.unidata.ucar.edu/software/netcdf/examples/files.html

Compliance Testing

It will be important to have some way to test whether a given client or server complies with the WCS specification when employing the CF-netCDF profile. In general, ensuring adherence to WCS is an issue separate from the CF-netCDF encoding. In order to test whether the netCDF encoded file transferred via a WCS getCoverage request complies with CF conventions, a CF conventions compliance test is available at:

CF-netCDF Compliance:
http://badc.nerc.ac.uk/help/formats/netcdf/index_cf.html

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NetCDF (network Common Data Form) with CF (Climate and Forecast) Conventions