Changes between Version 134 and Version 135 of WKTRaster/SpecificationWorking03

Timestamp:

07/08/11 09:02:27 (13 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking03

@@ -243 +243 @@
   -'UNION' (the extent of the union of both rasters).
 
- * In certain cases, for example when the computation extent is set to 'INTERSECTION', it is better to reduce the execution of ST_Mapalgebra(rast1, rast2) to overlapping rasters. This reduction is performed by adding a 'WHERE ST_Intersects(raster, raster)' clause to the query (to be implemented). If such a clause is not used and the rasters don't overlap an empty raster is returned. This behaviour is similar to the one of ST_Intersection(). Hence:[[BR]][[BR]]   SELECT ST_MapAlgebra(rast1, rast2, mathExpr) FROM mytable WHERE ST_Intersects(rast1, rast2)[[BR]] should be much faster and return many less empty rasters than:[[BR]][[BR]]  SELECT ST_MapAlgebra(rast1, rast2, mathExpr) FROM mytable 
+ * In certain cases, for example when the computation extent is set to 'INTERSECTION', it is better to reduce the execution of ST_Mapalgebra(rast1, rast2) to overlapping rasters. This reduction is performed by adding a 'WHERE ST_Intersects(raster, raster)' clause to the query (to be implemented). If such a clause is not used and the rasters don't overlap an empty raster is returned. This behaviour is similar to the one of ST_Intersection(). Hence:[[BR]][[BR]]
+  SELECT ST_MapAlgebra(rast1, rast2, mathExpr) FROM mytable WHERE ST_Intersects(rast1, rast2)[[BR]][[BR]]
+ should be much faster and return many less empty rasters than:[[BR]][[BR]]
+  SELECT ST_MapAlgebra(rast1, rast2, mathExpr) FROM mytable 
 
  * Alternative expressions, evaluated in place of the main expression, can be provided as parameter to deal with nodata values: