1 WCS Encoding Format Profiles netCDF Example Stefano Nativi, Lorenzo Bigagli, Ben Domenico, John Caron March 2006 Draft based mainly on presentations by Stefano Nativi and Lorenzo Bigagli at the OGC Technical Committee Meeting in Bonn

2 What is a WCS Encoding Format Profile? 1.A complete, formal specification of the encoding format using an accepted standard language e.g., GML. (Something a WCS client program can interpret unambiguously), OR 2.A brief document with enough information to enable someone to construct a WCS client to be able to access and use the data. (Something a human can read, understand and use to create a useful WCS client program.)

3 Draft netCDF Profile Role Human readable document with enough information to construct a client that can use the array of numbers in the coverage. Allows for more complete, machine readable, GML-based specifications such as ncML-GML, CSML, and perhaps GMLJP2

4 Draft netCDF Profile Content Provides pointers to disciplinary semantics (Coverage Range: What parameter or physical entity the numbers represent along with units of measure) Describes how spatial-temporal semantics can be determined ( Coverage domain: The Where and When of the numbers) Describes how syntax can be determined (The Order in which the numbers are transferred or stored.)

5 CF Conventions for netCDF Climate and Forecast (CF) Conventions in wide use in FES (Fluid Earth Sciences -- mainly atmospheric science and oceanography) Provides controlled vocabulary for disciplinary (Range) metadata with canonical units of measure Standard CF name table: CF name table:

6 WCS and netCDF Characteristics WCS CoveragenetCDF GeneralnetCDF with CF At least 2 spatial dimensions, optional 3rd spatial dimension, optional time dimension Arbitrary number of dimensions (i.e.axes). One dimension can be unlimited. No lower limit on dimensions. Up to 3 spatial dimensions, one time dimension Coverage range - set of values representing one entity Arbitrary number of dimensions (i.e.axes). One dimension can be unlimited. Arbitrary number of scalar variables representing multiple entities. A "standard_name" attribute maps variable names to a controlled set of names in the CF conventions name table. CF conventions name table. Coverage range has single unit of measure Each variables can have a different unit of measure Each variables can have a different unit of measure. Units of measure must conform to CF conventions Grid geometry irregularly spaced Grid geometry regularly spaced

7 WCS, netCDF Characteristics (contd) WCS CoveragenetCDF GeneralnetCDF with CF (x,y,z,t) domain shapeDimensions do not have any pre-specified order, so the shape is arbitrary except that the unlimited dimension must be first.. CF conventions recommends that dimensions be ordered according to *TZYX (§2.4); also note that a time-series of soundings depending on pressure and location, with time modelled as the unlimited dimension, does not follow this recommendation. Explicit geolocation metadataGeolocation optionalImplicit geo-location metadata. Must conform to CF conventions. Grid geometry regularly spaced Arbitrary grid geometryGrid geometry can be irregularly spaced Etc.