[postgis-devel] [PostGIS] #866: [raster] Change the ST_MapAlgebra nodatavalueexpr text parameter for nadatavaluerepl

[PostGIS]

#866: [raster] Change the ST_MapAlgebra nodatavalueexpr text parameter for
nadatavaluerepl
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 Reporter:  pracine         |       Owner:  pracine      
     Type:  defect          |      Status:  new          
 Priority:  blocker         |   Milestone:  PostGIS 2.0.0
Component:  postgis raster  |     Version:  trunk        
 Keywords:                  |  
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 The original plan to support refering to neighbour pixel in Mapalgebra was
 to refer to them using their position relative to the pixel being compute.
 e.g.: "rast[-1,0] + 1" rast[-1,0] refering to the first pixel at the left
 of the pixel being computed. This prove to be hard to use when the desired
 neighbour area include most pixels of an area larger than the first
 neighbour.

 The better alternative is to propose a variant to ST_MapAlgebra named
 ST_MapAlgebraNgb which would pass a vector of value (or a small raster) to
 a user defined summarizing function that would return the value to be
 assigned to the pixel.

 The original ST_MapAlgebra nodatavalueexpr text parameter was intented to
 give a way to provide an alternative expression in case one pixel value
 refered by the relative neighbour syntax (rast[-1,0]) would be nodata.

 Since this syntax will not be offered/implemented there is no more need
 for a nodatavalueexpr, a more simple nodatavaluereplacement value is
 sufficient.

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/866>
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