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|
----------------------------------------------------------------------
--
--
-- Copyright (c) 2009-2010 Pierre Racine <pierre.racine@sbf.ulaval.ca>
--
----------------------------------------------------------------------
-- NOTE: The ST_Reclass() function is already implemented in C. This plpgsql script is provided only as an example.
-- Defining the plpgsql function below might overwrite the current C implementation and brake other functions dependent on it.
-- Use with caution.
----------------------------------------------------------------------
CREATE OR REPLACE FUNCTION ST_Reclass(rast raster,
band int,
reclassexpr text)
RETURNS raster AS
$$
DECLARE
-- Create a new raster without the band we will reclassify
newrast raster := ST_DeleteBand(rast, band);
-- Determine the nodata value
nodataval float8 := ST_BandNodataValue(rast, band);
-- First parse of the reclass expression. Split the reclass classes into an array.
reclarray text[] := string_to_array(reclassexpr, '|');
-- Determine the number of classes.
nbreclassstr int := array_length(reclarray, 1);
-- Initialise the MapAlgebra expression
maexpr text := 'CASE ';
-- Temporary container for the two part of the class being parsed.
reclassstr text[];
-- Temporary array containing the splited class.
fromstr text[];
i int;
BEGIN
-- For each classes
FOR i IN 1..nbreclassstr LOOP
-- Split the class into an array of classes.
reclassstr := string_to_array(reclarray[i], ':');
IF array_length(reclassstr, 1) < 2 THEN
RAISE EXCEPTION 'ST_Reclass: Invalid reclassification class: "%". Aborting', reclarray[i];
END IF;
-- Split the range to reclassify into two
fromstr := string_to_array(reclassstr[1], '-');
-- Replace nodata with the nodata value
IF upper(reclassstr[2]) = 'NODATA' THEN
reclassstr[2] = nodataval::text;
END IF;
-- Build the maexpr expression
IF fromstr[2] IS NULL OR fromstr[2] = '' THEN
maexpr := maexpr || ' WHEN ' || fromstr[1] || ' = rast THEN ' || reclassstr[2] || ' ';
ELSE
maexpr := maexpr || ' WHEN ' || fromstr[1] || ' <= rast AND rast < ' || fromstr[2] || ' THEN ' || reclassstr[2] || ' ';
END IF;
END LOOP;
maexpr := maexpr || 'ELSE rast END';
newrast := ST_AddBand(rast, ST_MapAlgebra(rast, band, maexpr), 1, band);
RETURN newrast;
END;
$$
LANGUAGE 'plpgsql';
SELECT ST_Value(ST_TestRaster(1, 1, 4),1,1)
SELECT ST_Value(ST_Reclass(ST_TestRaster(1, 1, 4), 1, '1:2|2:2|3-5:10'), 1, 1);
|
