Changes between Version 81 and Version 82 of WKTRaster/SpecificationWorking01

Timestamp:

Dec 18, 2009, 1:45:39 PM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -235 +235 @@
  '''Implementation details'''
 
- This function could be roughly implemented as a SQL or PL/pgSQL function looking like 'SELECT ST_Collect(ST_AsPolygon(raster))'. For sure a more specialised version could be faster than ST_AsPolygon.
+ This function could be roughly implemented as a SQL function looking like 'SELECT ST_Collect((ST_AsPolygon(raster)).geom)'. For sure a more specialised version could be faster than ST_AsPolygon.
 
 '''ST_AsPolygon(raster) -> polygon geometry set''' - Returns a set of geometry, one for each group of pixel having the same value.
@@ -249 +249 @@
  This function is at the base of the first version of ST_Intersection which compute the intersection between a raster and a geometry.
 
- To avoid linking directly with PostGIS (see "Why avoid to link with PostGIS?" below) It should be implemented as a PL/pgSQL wrapper around ST_AsWKTPolygon() looking something like this:
+ To avoid linking directly with PostGIS (see "Why avoid to link with PostGIS?" below) It should be implemented as a SQL wrapper around ST_AsWKTPolygon() looking something like this:
 
  CREATE TYPE geomval AS (geom geometry, val float8);
  CREATE TYPE wktgeomval AS (wktgeom text, val float8);
 
- CREATE OR REPLACE FUNCTION ST_AsPolygon(rast) RETURNS SETOF geomval AS
- $BODY$
- DECLARE
-     pl geomval%rowtype;
- BEGIN
-     FOR pl IN SELECT ST_GeomFromText(wktgeomval.wktgeom), wktgeomval.val FROM ST_Dump(ST_GeomFromText(txtgeom)) AS wktgeomval 
-     LOOP
-        RETURN NEXT pl;
-     END LOOP;
-     RETURN;
- END
- $BODY$
- LANGUAGE 'plpgsql';
+ CREATE OR REPLACE FUNCTION ST_AsPolygon(rast raster) RETURNS SETOF geomval AS $$
+     SELECT ST_GeomFromText(wktgeomval.wktgeom), wktgeomval.val FROM ST_AsWKTPolygon(%1) AS wktgeomval;
+ $$ LANGUAGE SQL;
 
  So it can then be used like this:
 
  SELECT (ST_AsPolygon(rast)).val, (ST_AsPolygon(rast)).geom FROM sometable
+
+ or like this (maybe faster, to verify):
+
+ SELECT (gv).val, (gv).geom FROM (SELECT ST_AsPolygon(rast) gv FROM sometable) foo
+
 
 '''ST_AsWKTPolygon(raster) -> text set''' - Returns a set of text representation of geometry, one for each group of pixel having the same value.