[postgis-devel] [PostGIS] #2030: [raster] n-raster ST_MapAlgebra

PostGIS trac at osgeo.org
Fri Oct 5 10:32:01 PDT 2012

#2030: [raster] n-raster ST_MapAlgebra
 Reporter:  dustymugs    |       Owner:  dustymugs    
     Type:  enhancement  |      Status:  assigned     
 Priority:  medium       |   Milestone:  PostGIS 2.1.0
Component:  raster       |     Version:  trunk        
 Keywords:               |  

Comment(by pracine):

 Replying to [comment:6 dustymugs]:
 > distancex and distancey are for passing neighborhoods to the callback,
 not just the pixel value of interest.

 So you will replace ST_MapAlgebraFct (1 band version), ST_MapAlgebraFct (2
 band version) and ST_MapAlgebraFctNgb (1 band version). Right?

 Are the existing signatures going to be mapped to the new function or we
 will have to rewrite all our custom functions?

 > customextent is so that the user can specify an extent that they want.
 It is in essence a filter and as a side-affect permits correct coverage

 Can we call it a "mask"?

 In essence your multiband MapAlgebra is really what it is, a multiband map
 algebra. But I would add "intra-raster" multiband meaning the main goal is
 to do a computation involving many bands generally from the same raster. I
 can not think, and you did not show an application, where, say, three
 rasters would come from three different raster tables involving two joins
 and a multitude of possible resulting extents. My point here is to ask:
 Why not making a simpler multiband mapalgebra working only on the bands of
 a same raster? No need to pass many rasters (just an array of band index)
 and hence no need to create a new type. A much simpler function signature.
 No hassle with the possible extent since they are always identical. No
 braking of the existing mapalgebra (which work very well right now)... I
 generally tend not to complexify things if I don't have a useful user
 case. And I don't think it would be efficient and wise to join three
 raster coverages.

Ticket URL: <https://trac.osgeo.org/postgis/ticket/2030#comment:7>
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