[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
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Reporter: pracine | Owner: dustymugs
Type: task | Status: assigned
Priority: critical | Milestone: PostGIS 2.0.0
Component: postgis raster | Version: trunk
Keywords: |
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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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