[postgis-devel] [PostGIS] #1119: [raster] Modify ST_MapAlgebra so that expressions can refer to any band

PostGIS trac at osgeo.org
Fri Feb 3 06:43:36 PST 2012

#1119: [raster] Modify ST_MapAlgebra so that expressions can refer to any band
 Reporter:  pracine      |       Owner:  pracine              
     Type:  enhancement  |      Status:  new                  
 Priority:  low          |   Milestone:  PostGIS Raster Future
Component:  raster       |     Version:  trunk                
 Keywords:               |  

Comment(by pracine):

 This is a big change that we should definitely be postpone to future

 -It requires to remove the band parameter to every sT_MapAlgebra:
 since we can invoke any band in the expression, there is no need to pass a
 band number to the function.

 -As commented previously in this ticket, it drastically changes the
 meaning of the nodata alternate expression. The nodata expressions are
 there to tell what to do when the pixel iterator meet a nodata value. If
 there is no more band parameter, which pixel of which band we must
 consider as a nodata value?

 I think more and more that the way ST_MapAlgebra was designed must stick
 with dealing with one band at a time. We should design new map algebra
 function to deal with 1) expressions referencing multiple bands (this is
 the possibility invoked in this ticket) and 2) map algebra for multiple
 band raster applying the same expression to every bands of a raster.

 So please think twice before implementing this feature. We need new
 ST_MapAlgebra variants with specific behaviors.

Ticket URL: <http://trac.osgeo.org/postgis/ticket/1119#comment:6>
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