Unidata's THREDDS Project
The THREDDS project is developing middleware to bridge the gap between data providers and data users. The goal is to simplify the discovery and use of scientific data and to allow scientific publications and educational materials to reference scientific data. The mission of THREDDS is for students, educators and researchers to publish, contribute, find, and interact with data relating to the Earth system in a convenient, effective, and integrated fashion.
The THREDDS project consists mainly of two software packages and two related XML encodings:
- the netCDF-Java/CDM library;
- the NetCDF Markup Language (NcML);
- the THREDDS Data Server (TDS); and
- the THREDDS Catalog specification.
Source code for each of these is available from GitHub at
The latest released and snapshot software artifacts (.jar and .war files e.g.) are available from Unidata's Maven repositories
Copyright and licensing information can be found here
as well as in the LICENSE.txt file accompanying the software.
More details on each of these can be found below.
The netCDF Java library provides an interface for scientific data access. It can be used to read scientific data from a variety of file formats including netCDF, HDF, GRIB, BUFR, and many others. By itself, the netCDF-Java library can only write netCDF-3 files. It can write netCDF-4 files by using JNI to call the netCDF-C library. It also implements Unidata's Common Data Model (CDM) to provide data geolocation capabilities.
For more information about netCDF-Java/CDM, see the netCDF-Java web page at
and the CDM web page at
You can obtain a copy of the latest released version of netCDF-Java software from
More documentation can be found at
A mailing list, email@example.com, exists for discussion of all things netCDF-Java/CDM including announcements about netCDF-Java/CDM bugs, fixes, enhancements, and releases. For information about how to subscribe, see the "Subscribe" link on this page
For more general netCDF discussion, see the firstname.lastname@example.org email list.
We appreciate feedback from users of this package. Please send comments, suggestions, and bug reports to email@example.com. Please identify the version of the package.
NetCDF Markup Language (NcML)
NcML is an XML representation of netCDF metadata, it approximates the header information one gets from a netCDF file with the "ncdump -h" command. NcML is similar to the netCDF CDL (network Common data form Description Language), except, of course, it uses XML syntax.
Beyond simply describing a netCDF file, it can also be used to describe changes to existing netCDF files. A limited number of tools, mainly netCDF-Java based tools, support these features of NcML
For more information about NcML, see the NcML web page at
THREDDS Data Server (TDS)
The THREDDS Data Server (TDS) provides metadata and data access to scientific datasets. Datasets can be served through OPeNDAP, OGC's WMS and WCS, HTTP, and other remote data access protocols. It can be configured to aggregate a collection of datasets so the collection is seen as a single dataset when viewed through the various data access protocols. The TDS is a server-based system that can be easily installed in any servlet container such as Apache Tomcat.
For more information about the TDS, see the TDS web page at
You can obtain a copy of the latest released version of TDS software from
A mailing list, firstname.lastname@example.org, exists for discussion of the TDS and THREDDS catalogs including announcements about TDS bugs, fixes, enhancements, and releases. For information about how to subscribe, see the "Subscribe" link on this page
We appreciate feedback from users of this package. Please send comments, suggestions, and bug reports to email@example.com. Please identify the version of the package.
THREDDS Catalogs can be thought of as representing logical directories of on-line data resources. They are encoded as XML and provide a place for annotations and other metadata about the data resources. These XML documents are how THREDDS-enabled data consumers find out what data is available from data providers.
THREDDS Catalog documentation (including the specification) is available at