NetCDF Status

Russ Rew, Ed Hartnett, and Dennis Heimbigner
October 1, 2009

This report updates the last status report of Unidata's netCDF and OPeNDAP development efforts since the Policy Committee meeting in May 2009.

NetCDF and Unidata

NetCDF efforts are associated with Theme 2: Advancing data services from the Unidata 2013 proposal. NetCDF continues to serve as a key infrastructure element for data providers and users of climate, atmosphere, and ocean data. Recent netCDF developments improve client access to remote data services, documentation, portability, ease of use, interoperability with other data representations, and performance on high-end platforms.

The netCDF-OPeNDAP SDCI Project

We have completed work on the NSF-funded cyberinfrastructure project for improving OPeNDAP and netCDF integration, by integrating a DAP client library with the latest netCDF releases (4.1-beta), accomplishing the first goal of the project, to enhance Unidata's netCDF C library to support the OPeNDAP protocol as the remote access protocol for netCDF data.

Using this software, it is now possible for a C or Fortran program (such as GrADS or IDL) built using the Unidata netCDF C-based library to access specified subsets of remote data in a variety of formats provided by OPeNDAP servers, including Unidata's THREDDS Data Server.

Another goal of the project is to extend the OPeNDAP data model and protocol to support the Unidata Common Data Model on the server side as well as the client side. We collaborated in specifying the extended OPeNDAP data model, which is being supported by the DAP4 protocol implemented by

With, we applied to NSF for and were awarded supplemental funding for this project, supporting further work on scientific data streaming.

The netCDF C-based libraries

Since the last status report, version netCDF version 4.0.1 was released and two beta releases of version 4.1 were made available.

Version 4.0.1 added performance enhancements, an upgraded Fortran 90 API, ncdump handling of netCDF-4 features, bug-fixes, and portability improvements, and included experimental releases of a netCDF-4 version of the ncgen utility and the OPeNDAP client library for intrepid users to gain early access to these new features.

In addition to bug fixes and documentation improvements, version 4.1 adds

(Note: status for the independent netCDF-Java development effort is summarized in the THREDDS status report.)

NetCDF and the CF Conventions

Work continued on developing libcf, a library for supporting the widely used CF metadata conventions for model output, observational data, and derived products. CF metadata conventions provide a means of georeferencing arrays and adding semantics. Conventions that select a single way to represent such metadata make it practical to write software that “understands” the metadata. The resulting uniformity of access supports building applications with powerful extraction, regridding, analysis, visualization, and processing capabilities.

We continued development of the F90 API for the CF library, added new tests, incorporated changes for the GridSpec library for structured grids from GFDL, and successfully proposed additional libcf development to support integrated modeling environments and workflows as part of NOAA's Global Interoperability Program.

In addition, we participated in bi-monthly CF Governance teleconferences, wrote a draft CF standard (now under review) for the NASA Earth Science Data Systems standards group, and participated in discussion of CF issues at the 8th annual GO-ESSP meeting.

The NetCDF Training Workshop

In August, we organized and presented two NetCDF Workshops for Developers and Data Providers for 68 participants (the largest ever), which included meeting with most participants and discussing their individual needs. We also made workshop materials available online for remote netCDF training.

Other Notes

In June, we wrote and published a new set of Frequently Asked Questions, "Formats, Data Models, and Software Releases", to clear up confusion about various netCDF data models, software, and formats, in particular questions about netCDF-4 versus netCDF-3. The FAQ offers detailed guidance to users about which version to build and install.

Russ presented a talk in June on "NetCDF and Scientific Data Durability" at an ESIP Federation meeting on data stewardship and preservation.

Google now shows that 1.36 million web pages and 2,180 books mention netCDF. The Ocean Observing Initiative Cyberinfrastructure (CI) project specifies that the external data file formats that can be generated from the CI data model will include netCDF-4 and netCDF classic, because "This format is so prevalent in the community that it rises to the level of a requirement."

by Russ Rew