[postgis-devel] [PostGIS] #590: [raster] Two rasters version of ST_MapAlgebra

PostGIS trac at osgeo.org
Sat Oct 22 09:20:23 PDT 2011

#590: [raster] Two rasters version of ST_MapAlgebra
 Reporter:  pracine         |       Owner:  dustymugs    
     Type:  task            |      Status:  assigned     
 Priority:  critical        |   Milestone:  PostGIS 2.0.0
Component:  postgis raster  |     Version:  trunk        
 Keywords:                  |  

Comment(by bnordgren):

 I would observe a few things:

  1. This is a two ''band'' operation, not a two ''raster'' operation.
 Bands have "nodata scalars". Rasters have "nodata vectors".
  1. Perhaps we should have an output_nodata parameter which defaults to
 the "automatic" scheme described by Pierre, above, but which allows the
 user to specify a value if they feel like it.
  1. There is no reason whatsoever to assume that the two bands passed to
 this function come from the same table (and hence are imagined to be
 aligned for some special case). In fact, it will probably be common to
 combine tiles from different images.
  1. There is nothing (and should be nothing) requiring rasters from the
 same table to be aligned (or even to have the same SRID). The data in the
 raster_columns table is informative, not normative. As Pierre once told
 me, there is no guarantee that someone didn't insert a rogue raster and
 mess up your nice table. If you are in fact shooting for "one table per
 logical theme", you'd better allow for that theme to be global and the
 table to contain all the UTM zones. One table per theme per UTM zone is
 insanity personified. Perhaps this should be broken off as a separate
 discussion. Is there any code which actually depends on all tiles in an
 individual table being of the same SRID and aligned?

 PS: If you're still interested in implementing this using to kick the
 tires on the raster iterator engine, I'm available to help.

Ticket URL: <https://trac.osgeo.org/postgis/ticket/590#comment:15>
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