[postgis-users] Updated cleangeometry function

[Paul Pfeiffer]

I have been having problems with the clean geometry function referenced at
http://trac.osgeo.org/postgis/wiki/UsersWikiCleanPolygons returning null
geometries. So I have fixed the script and I'm providing it below if anyone
else wants to test it and let me know I could update the wiki.

(Requires Postgres v9 +)

-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-- 
-- $Id: cleanGeometry.sql 2014-01-16 Paul Pfeiffer
--
-- cleanGeometry - remove self- and ring-selfintersections from
--                 input Polygon geometries
-- 
-- Copyright 2014 Paul Pfeiffer
-- Version 2.0
-- contact: nightdrift at gmail dot com
-- 
-- modified from cleanGeometry.sql 2008-04-24 from http://www.kappasys.ch
--
-- This is free software; you can redistribute and/or modify it under
-- the terms of the GNU General Public Licence. See the COPYING file.
-- This software is without any warrenty and you use it at your own risk
--
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


CREATE OR REPLACE FUNCTION cleangeometry(geom "public"."geometry")
    RETURNS "public"."geometry" AS
$BODY$
    DECLARE
    inGeom ALIAS for $1;
    outGeom geometry;
    tmpLinestring geometry;
    sqlString text;

BEGIN

    outGeom := NULL;

    -- Clean Polygons --
    IF (ST_GeometryType(inGeom) = 'ST_Polygon' OR ST_GeometryType(inGeom) =
'ST_MultiPolygon') THEN

        -- Check if it needs fixing
        IF NOT ST_IsValid(inGeom) THEN

            sqlString := '
                -- separate multipolygon into 1 polygon per row
                WITH split_multi (geom, poly) AS (
                    SELECT
                        (ST_Dump($1)).geom,
                        (ST_Dump($1)).path[1] -- polygon number
                ),
                -- break each polygon into linestrings
                split_line (geom, poly, line) AS (
                    SELECT
                        ST_Boundary((ST_DumpRings(geom)).geom),
                        poly,
                        (ST_DumpRings(geom)).path[1] -- line number
                    FROM split_multi
                ),
                -- get the linestrings that make up the exterior of each
polygon
                line_exterior (geom, poly) AS (
                    SELECT
                        geom,
                        poly
                    FROM split_line
                    WHERE line = 0
                ),
                -- get an array of all the linestrings that make up the
interior of each polygon
                line_interior (geom, poly) AS (
                    SELECT
                        array_agg(geom ORDER BY line),
                        poly
                    FROM split_line
                    WHERE line > 0
                    GROUP BY poly
                ),
                -- use MakePolygon to rebuild the polygons
                poly_geom (geom, poly) AS (
                    SELECT
                        CASE WHEN line_interior.geom IS NULL
                            THEN
ST_Buffer(ST_MakePolygon(line_exterior.geom), 0)
                            ELSE
ST_Buffer(ST_MakePolygon(line_exterior.geom, line_interior.geom), 0)
                        END,
                        line_exterior.poly
                    FROM line_exterior
                    LEFT JOIN line_interior USING (poly)
                )
            ';

            IF (ST_GeometryType(inGeom) = 'ST_Polygon') THEN
                sqlString := sqlString || '
                    SELECT geom
                    FROM poly_geom
                ';
            ELSE
                sqlString := sqlString || '
                    , -- if its a multipolygon combine the polygons back
together
                    multi_geom (geom) AS (
                        SELECT
                            ST_Multi(ST_Collect(geom ORDER BY poly))
                        FROM poly_geom
                    )
                    SELECT geom
                    FROM multi_geom
                ';
            END IF;

            EXECUTE sqlString INTO outGeom USING inGeom;

            RETURN outGeom;
        ELSE
            RETURN inGeom;
        END IF;

    -- Clean Lines --
    ELSIF (ST_GeometryType(inGeom) = 'ST_Linestring') THEN

        outGeom := ST_Union(ST_Multi(inGeom), ST_PointN(inGeom, 1));
        RETURN outGeom;
    ELSIF (ST_GeometryType(inGeom) = 'ST_MultiLinestring') THEN
        outGeom := ST_Multi(ST_Union(ST_Multi(inGeom), ST_PointN(inGeom,
1)));
        RETURN outGeom;
    ELSE
        RAISE NOTICE 'The input type % is not
supported',ST_GeometryType(inGeom);
        RETURN inGeom;
    END IF;
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE COST 100
;
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