Name

ST_BuildArea — Creates an areal geometry formed by the constituent linework of given geometry

Synopsis

geometry ST_BuildArea(geometry A);

Description

Creates an areal geometry formed by the constituent linework of given geometry. The return type can be a Polygon or MultiPolygon, depending on input. If the input lineworks do not form polygons NULL is returned. The inputs can be LINESTRINGS, MULTILINESTRINGS, POLYGONS, MULTIPOLYGONS, and GeometryCollections.

This function will assume all inner geometries represent holes

[Note]

Input linework must be correctly noded for this function to work properly

Availability: 1.1.0

Examples

This will create a donut

SELECT ST_BuildArea(ST_Collect(smallc,bigc))
FROM (SELECT
    ST_Buffer(
      ST_GeomFromText('POINT(100 90)'), 25) As smallc,
    ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) As bigc) As foo;
                

This will create a gaping hole inside the circle with prongs sticking out

SELECT ST_BuildArea(ST_Collect(line,circle))
FROM (SELECT
    ST_Buffer(
        ST_MakeLine(ST_MakePoint(10, 10),ST_MakePoint(190, 190)),
                5)  As line,
    ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) As circle) As foo;

--this creates the same gaping hole
--but using linestrings instead of polygons
SELECT ST_BuildArea(
    ST_Collect(ST_ExteriorRing(line),ST_ExteriorRing(circle))
    )
FROM (SELECT ST_Buffer(
    ST_MakeLine(ST_MakePoint(10, 10),ST_MakePoint(190, 190))
        ,5)  As line,
    ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) As circle) As foo;

                

See Also

ST_Node, ST_MakePolygon, ST_BdPolyFromText, ST_BdMPolyFromTextwrappers to this function with standard OGC interface