[postgis-devel] [raster] More architecture

[Bryce L Nordgren]

Fleshed out the UML diagrams pertaining to the "SpatialCollection" type (the
workhorse behind raster-returning spatial operations which don't vectorize
first.) Made a distinction between "plain" collections and "virtual"
collections which may be combinations of other collections (e.g., spatial
operations.) While it's presented in the context of the raster iteration
engine, the iteration engine essentially evaluates one of these virtual
collections (e.g., operations) on a regular grid defined by the resultant
raster. The virtual collection, however, can compute values for any location
(e.g., so if you're interested in a few key locations, there's no need to
compute and return an entire raster worth of results.)

This may be applicable to non-raster-returning spatial operations as well,
but I have not yet thought that far ahead.

http://trac.osgeo.org/postgis/wiki/WKTRaster/SeamlessArchitecture#Spatialcollectiondesign

Bryce
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