CDM & TDS Data Server: Earth & Ocean Sciences Meet GIS

John Caron (Unidata/UCAR) with Ethan Davis (Unidata), Lansing Madry (Unidata)

12:30 on Friday 20th September (in Session 33, starting at 11:30 a.m., EMCC: Room 4)

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Description: The Common Data Model and the THREDDS Data Server provide metadata and data access for scientific datasets using several remote data access protocols (OpeNDAP, NetCDF Subset Service, WMS, WCS) and have become an essential tool for interdisciplinary data sharing within the various domains of geosciences.

Different geoscience disciplines have developed sophisticated domain-specific cyber infrastructures for data storage, manipulation, and visualization. NetCDF, HDF, and GRIB are multi-dimensional array-based data formats widely used in meteorology and oceanography. However, these formats are not fully compatible with the visualization and manipulation tools supported by Geographic Information Systems (GIS), which caters to the discrete vector features and 2D raster formats commonly used in the geography, hydrology, and cartography. By providing a higher level of abstraction and enabling spatial, rather than indexed, data access, the Unidata Common Data Model (CDM) facilitates integration of NetCDF, HDF, and GRIB data into GIS tools, fostering interdisciplinary communication. The THREDDS Data Server (TDS) utilizes the CDM to work efficiently with large, dynamic collections of observational and model data. The TDS organizes these collections into unified, logical datasets, simplifying their access and dissemination. TDS datasets are exposed via the WMS and WCS Open Geospatial Consortium specifications, with support for time and elevation standard dimensions. Alternatively, TDS datasets are accessible through specialized web services that provide subsetting capabilities. The NetCDF Subset Service allows for spatial subsetting, while OpenDAP subsets by index. Finally, metadata discovery systems such as Geoportal and GI-CAT harvest TDS catalog metadata. The TDS ncISO service also serves catalog metadata directly as ISO documents, enabling text searches and exposing a CSW interface on TDS instances through these discovery systems. The CDM & TDS are OpenSource projects ( with strong community support. Members have contributed key features, including the ncISO and WMS implementations. Moreover, many interdisciplinary Web-GIS applications have already been successfully developed combining TDS web services with resources from other spatial data infrastructures. Coupled with Unidata's governing committees, the projects provide a unique framework that establishes quality standards and ensures that development meets community needs.