[postgis-devel] [PostGIS] #1176: [raster] Two raster ST_Intersects

[PostGIS]

#1176: [raster] Two raster ST_Intersects
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 Reporter:  dustymugs       |       Owner:  dustymugs    
     Type:  enhancement     |      Status:  assigned     
 Priority:  medium          |   Milestone:  PostGIS 2.0.0
Component:  postgis raster  |     Version:  trunk        
 Keywords:                  |  
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Comment(by bnordgren):

 Oh my. That seems complicated. May I offer an alternative algorithm which
 should mean less operations per pixel? It may be too simple or not cover a
 use case, so please blast away at it. It's pseudocode so holler out if
 anything is unclear.


 {{{
 if (A.SRID != B.SRID) return false;
 grid_overlaps := convex hull of A overlaps convex hull of B.
 if (no bands have been provided) {
   return grid_overlaps;
 } else {
   if (not grid_overlaps) return false ;

   smaller := A or B, depending on which raster has fewer pixels;
   big     := the other raster
   for smaller_j := 1,small_HEIGHT {
      for smaller_i := 1, small_WIDTH {
          (big_i, big_j) = big_geopoint2cell(small_cell2geopoint(smaller_i,
 smaller_j))
          if ( 0 < big_i <= big_WIDTH) AND (0 < big_j <= big_HEIGHT) {
              round big_i and big_j to nearest integer indices ;
              if (big_getValue(big_i, big_j) != NODATA) {
                 return TRUE ;
              }
          }
      }
   }
 }
 return FALSE ;
 }}}

 This could address the special case where one raster fits completely
 within one cell of the other if we make sure that the selection of
 "smaller" does not allow the pixelsize of "smaller" to be larger than the
 whole "bigger" raster.

 So maybe the criteria for "smaller" would be "which raster has the minimum
 pixel size", and if there's a tie: "which raster has fewer pixels"?



 Note, I implemented the rt_raster_geopoint_to_cell(), offloaded both
 forward and backwards transformations to GDAL, and made sure the code uses
 the accessor methods instead of the fields here:

 https://github.com/bnordgren/postgis/commit/ab632411b303aca898c285c53e428060ea9e35de

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/1176#comment:7>
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