in progress
netCDF/OPeNDAP are the perfect web file format/web service for gridded data. Gridded data exist in various types.
- Single grid vs. tiled grids
- Single grid coverages: one file contains all the data of the entire space covered by the dataset.
- A set of tiled grid coverages: one file contains only the data of a subset of the entire space covered by the dataset. The entire space is . Example:
http://opendap.deltares.nl/thredds/catalog/opendap/rijkswaterstaat/jarkus/grids/catalog.html
http://opendap.deltares.nl/thredds/catalog/opendap/rijkswaterstaat/vaklodingen/catalog.html
http://opendap.deltares.nl/thredds/catalog/opendap/rijkswaterstaat/kustlidar/catalog.html
- Grid topology
- Orthogonal grid
- An orthogonal lat-lon grid: climate data products often appear in this topology. There is a separate lat vector (e.g. -180:1:180 deg) and a separate lon vector (e.g. -90:1:90 deg) that span a part of the globe. Support for these grids is always available. Example:
http://opendap.deltares.nl/thredds/catalog/opendap/deltares/FEWS-IPCC/catalog.html - An orthogonal x-y grid: national data products often appear in this topology. There is a separate x vector (e.g. 0:100:280000 m)
) and a separate y vector (e.g. 624800:-100:300000) that span a part in a local projection. Support to plot these grids in lat-lon space is less often available, as it assumes that the client can deal with the two methods to prescribe lat-lon coordinates. The first, implicit option is assuming that the client can do the conversion from the local projection to the a WGS84 lat-lon projection. The CF convention describes how to add projection meta-data to the netCDF file (grid_mapping attribute). In addition, the data producer can transform the x and y vectors to complete lat and lon grids, prescribing the WGS84 position of each grid cell separately. The CF convention describes how to attach these global coordinates to the dataset (coordinates attribute). OpenEarth recommend to supply both options in netCDF files. This option is in fact the same as considering the orthogonal x-y grid as a curvi-linear lat-lon grid, as discussed next.
Example:
http://opendap.deltares.nl/thredds/catalog/opendap/tno/ahn100m/catalog.html
- An orthogonal lat-lon grid: climate data products often appear in this topology. There is a separate lat vector (e.g. -180:1:180 deg) and a separate lon vector (e.g. -90:1:90 deg) that span a part of the globe. Support for these grids is always available. Example:
- Curvi-linear grid: plotting support for curvi-linear grids depends on the client. Curvi-linear grids often exist, key examples are:
individual satellite images that are otrhogonal in pixel space, but fully warped in lat-lon space and (ii) curvi-linear coastal circulation models that are otrhogonal in grid index space, but that have been warped to fit local coast lines.
- A curvi-linear lat-lon mesh: Example:
- Orthogonal grid
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- A curvi-linear x-y mesh: Example:
- Unstructured grids: supprot for unstructured grids has not been standardized. Proposals fore
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- Time dependency
- Password restrictions
