PostGRID

This information is summarized from forums and mailing lists:

PostGRID (http://seagis.sourceforge.net/postgrid/) is a schema in a PostGIS database. It contains coverage metadata, not pixel values and is used as an index for fast coverage lookup:

• Which data are available (what, where, when…)‏
• How to get the data (filename, format…)‏
• What the pixel values means (categories…)‏

Images stay as files in their native format, e.g. NetCDF, geoTIFF

It can handle up to 4D data (x,y,z,t) and is also capable to apply some image operations. For example if we have a "Sea Surface Temperature (SST)" layer, PostGrid can manage a "SST Gradient" layer with coverages computed on the fly by applying the JAI "GradientMagnitude" operator on coverages from the "Sea Surface Temperature (SST)" layer.

The PostGrid database contains the following tables (amongst others):

• Layer A list of layers as in the WMS sense. Columns include "name" as varchar.
• GridGeometries A set of bounding boxes (as a PostGIS polygon) together with affine transforms coefficients for the "gridToCRS" math transform. This is a separate table because a lot of rasters share the same spatial geometries (e.g. time series).
• Categories Everything needed in order to create the GridSampleDimensions with "sampleToGeophysics" math transforms. This is required in order to performs analysis work (e.g. treat the Coverage as a set of data, not just an image).
• GridCoverages The list of rasters with foreign keys (directly or indirectly) to Layer, GridGeometries , Categories...

PostGRID has been applied in the WED-SAT project, http://www.ird.fr/informatique-scientifique/projets/wedsat.php?lang=en, which connects GeoServer to PostGRID.

-- JonBlower - 01 Feb 2008