[postgis-devel] Final section, raster architecture document

[Bryce L Nordgren]

The "Result Grid Iteration Engine".

https://collab.firelab.org/software/projects/modisfire/wiki/Seamless_spatial_operations_architecture#Result-Grid-Iteration-Engine

Finally, the top down design on my architecture wiki page meets the bottom
up design in the code on ticket 1058 (
http://trac.osgeo.org/postgis/ticket/1058). Note that the code is slightly
outdated because I had better ideas of how to organize it (due in part to
the exercise of writing the code in the first place).

Features:

   - The raster iteration code is in one place.
   - Small pieces (extension points) come together in a large thing
   (iteration engine).
   - MapAlgebra can leverage this design simply by implementing a value
   computation extension point.
   - Speed performance advantage over SQL implementation (input and output
   rasters are only serialized/deserialized once, instead of once per pixel).

The drawback, of course, is that it loads both input rasters and the output
raster completely into memory at the same time (assuming they are all
in-database rasters).

Bryce
PS: Mark, I have the postgis->lwgeom refactoring done on my laptop, but work
won't let me connect it to the network. I'll upload when I get home.
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