Changes between Version 139 and Version 140 of WKTRaster/SpecificationWorking03

Timestamp:

Jul 8, 2011, 11:27:07 AM (13 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking03

@@ -238 +238 @@
  * Both raster must be aligned. This is determined using the ST_SameAlignment() function described below. If a resampling is necessary they use the planned ST_Resample() function to resample the second raster to the first one before processing (or the first to the second if a MASTER parameter is provided). If ST_Resample() is not yet implemented when these functions are implemented, just return an error message: "ERROR:  MapAlgebra on rasters with different alignment not yet implemented."
 
- * The computation extent (extentexpr in the functions below) can be:
+ * The computation extent (extentexpr in the functions below) and hence the extent of the resulting raster can be:
 
   -'FIRST' (the extent of the first raster) (default),[[BR]]
@@ -249 +249 @@
  should be much faster and return many less empty rasters than:[[BR]][[BR]]
   SELECT ST_MapAlgebra(rast1, rast2, mathExpr) FROM mytable 
+
+ * The expression are evaluated by calling the equivalent or an EXECUTE SQL statement. “EXECUTE” in pl/pgsql or SPI_execute in C. This mechanism ensures that users can use any PostgreSQL function and operators in the expression as well as their own custom pl/pgsql functions. Raster values in the expressions are refered by “rast1” and “rast2”. Ex.: ST_MapAlgebra(raster1, band1, raster2, band2, “rast1 + cos(rast2) + 4”)
 
  * Alternative expressions, evaluated in place of the main expression, can be provided as parameter to deal with nodata values: