Overview of GALEON IE Phase 1
The GALEON OGC Network will continue the Phase 2 work of the GALEON Interoperability Experiment.
The original GALEON (Geo-interface to Atmosphere, Land, Earth, Ocean, NetCDF) WCS Interoperability Experiment (IE) was set up to implement a geo-interface to netCDF datasets via the WCS 1.0 protocol specification. One specific approach implemented the WCS as a layer above a set of client/server and catalog protocols already widely in use in the atmospheric and oceanographic sciences communities. In particular, it leverages the widespread base of OPeNDAP servers that provide access to netCDF datasets and accompanying THREDDS servers providing ancillary information about the datasets. The IE investigated the feasibility of adapting data and metadata originating from OPeNDAP/THREDDS servers to the WCS specifications, thus bridging the gap between the atmospheric, oceanographic and GIS communities, by alleviating data interoperability issues.
The GALEON Phase 1 experiment has delivered collections of numerical forecast model output which consist of what are sometime referred to as five dimensional or 5D grids (multiple parameters (e.g., temperature, pressure, relative humidity) varying in three spatial dimensions with two time coordinates (model run time and forecast time). It is important to note that, while it is convenient to refer to these as 5D datasets, the 3 spatial dimensions and temporal dimensions are fundamentally different in that they are part of the domain whereas the multiple parameters are part of the range in the WCS data models and interface specifications.
This IE can be seen as a step in the direction of interoperability with data systems already in existence in the oceanographic and atmospheric sciences. These technologies include netCDF, OPeNDAP, ADDE, and THREDDS. An outline of the integration path is given in:
The primary objectives of phase 1 IE have been to determine whether:
- a viable WCS getCapabilities geo-interface (gateway in earlier versions) can be built on existing THREDDS inventory catalog services
- the ncML-G data model is adequate for providing describeCoverage responses for netCDF datasets
- there are any solutions to the previously identified limitations to geoTIFF encoding format for representing from 5D netCDF files in such a way that the relationships among layers is preserved
- the proposed ncML-GML encoding format is a practical solution to serving 5D data from netCDF files, either embedded (ASCII or attached binary) or linked (OPeNDAP link or other URL)
- netCDF itself is a viable WCS binary encoding format
- existing WCS clients are able to access analyze and display 5D data from netCDF files
- 5D geospatial data sets can be served efficiently through standard database technology