ST_Polygonize
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## Name

ST_Polygonize — Computes a collection of polygons formed from the linework of a set of geometries.

## Synopsis

`geometry ST_Polygonize(`geometry set geomfield`)`;

`geometry ST_Polygonize(`geometry[] geom_array`)`;

## Description

Creates a GeometryCollection containing the polygons formed by the constituent linework of a set of geometries. Input linework must be correctly noded for this function to work properly.

To ensure input is fully noded use ST_Node on the input geometry before polygonizing.

GeometryCollections are often difficult to deal with with third party tools. Use ST_Dump to convert the polygonize result into separate polygons.

Performed by the GEOS module.

Availability: 1.0.0RC1

## Examples: Polygonizing single linestrings

    SELECT ST_AsEWKT(ST_Polygonize(geom_4269)) As geomtextrep
    FROM (SELECT geom_4269 FROM ma.suffolk_edges ORDER BY tlid LIMIT 45) As foo;

    geomtextrep
    -------------------------------------
     SRID=4269;GEOMETRYCOLLECTION(POLYGON((-71.040878 42.285678,-71.040943 42.2856,-71.04096 42.285752,-71.040878 42.285678)),
     POLYGON((-71.17166 42.353675,-71.172026 42.354044,-71.17239 42.354358,-71.171794 42.354971,-71.170511 42.354855,
     -71.17112 42.354238,-71.17166 42.353675)))
    (1 row)

    --Use ST_Dump to dump out the polygonize geoms into individual polygons
    SELECT ST_AsEWKT((ST_Dump(foofoo.polycoll)).geom) As geomtextrep
    FROM (SELECT ST_Polygonize(geom_4269) As polycoll
        FROM (SELECT geom_4269 FROM ma.suffolk_edges
            ORDER BY tlid LIMIT 45) As foo) As foofoo;

    geomtextrep
    ------------------------
     SRID=4269;POLYGON((-71.040878 42.285678,-71.040943 42.2856,-71.04096 42.285752,
    -71.040878 42.285678))
     SRID=4269;POLYGON((-71.17166 42.353675,-71.172026 42.354044,-71.17239 42.354358
    ,-71.171794 42.354971,-71.170511 42.354855,-71.17112 42.354238,-71.17166 42.353675))
    (2 rows)

## See Also

ST_Node, ST_Dump

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