[postgis-devel] [PostGIS] #903: [raster] ST_Reclass

[PostGIS]

#903: [raster] ST_Reclass
----------------------------+-----------------------------------------------
 Reporter:  dustymugs       |       Owner:  dustymugs            
     Type:  task            |      Status:  new                  
 Priority:  medium          |   Milestone:  PostGIS Raster Future
Component:  postgis raster  |     Version:  trunk                
 Keywords:                  |  
----------------------------+-----------------------------------------------

Comment(by dustymugs):

 I have two questions/concerns about the current concept.

 1. ST_Reclass() with a variable number of function parameters would be
 ideal.  But I don't believe pl/plgsql is able to do that.  It does support
 variadic arguments but nothing like C's argc and argv (as far as I can
 tell).  Variadic argument was added to PostgreSQL in 8.4 so I also wonder
 what is the minimum version that PostGIS supports.  If the minimum in 8.2
 or 8.3, variadic functions may not be an option.

 Maybe we should consider two separate approaches, one less efficient and
 one more so that may not be quite as friendly...

 ST_Reclass(rast raster, nband int, reclassexpr text, pixeltype text)

 This would be fine if you're only going to reclassify one band but is
 absolutely inefficient for multiple bands...

 {{{
 ST_Reclass(rast, 1, SOME_EXPRESSION, '8BUI')
 }}}

 and

 {{{
 ST_Reclass(
   ST_Reclass(
     ST_Reclass(
       ST_Band(rast, ARRAY[1,1,1])
       , 1, SOME_EXPRESSION, '8BUI'
     )
     , 2, SOME_EXPRESSION, '8BUI'
   )
   , 3, SOME_EXPRESSION, '8BUI'
 )
 }}}

 The second example is absolutely inefficient.  So, a more efficient method
 could be

 ST_Reclass(rast, reclassexpr_set text[])

 where reclassexpr_set is a two dimension array like

 ARRAY[
   [nband int, reclassexpr text, pixeltype text],

   [nband int, reclassexpr text, pixeltype text],

   ...

   [nband int, reclassexpr text, pixeltype text],
 ]

 2. I have a question about the range in the reclassexpr.

 If we look at the following, I wonder what the min(covmin, 0)-0 and
 0-max(covmax, 0) really means?

 min(covmin, 0)-0:0,0-max(covmax, 0):0-255

 Does it mean...

 min(covmin, 0) <= x < 0 and 0 <= x < max(covmax, 0)

 or

 min(covmin, 0) <= x <= 0 and 0 <= x <= max(covmax, 0)

 or

 min(covmin, 0) < x <= 0 and 0 < x <= max(covmax, 0)

 something else?

 So what happens when x is at the limit of the range?

 Thoughts?

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/903#comment:2>
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