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
Availability: 1.1.0 - requires GEOS >= 2.1.0.
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;
|