Description

Creates a Polygon or CurvePolygon formed by the given shell and optional array of holes. Input geometries must be closed LineStrings, CircularStrings, CompoundCurves, or NURBSCurves (rings). If any input ring is curved, the result is a CurvePolygon.

Variant 1: Accepts one shell ring.

Variant 2: Accepts a shell ring and an array of inner (hole) rings. A geometry array can be constructed using the PostgreSQL array_agg(), ARRAY[] or ARRAY() constructs.

	This function does not accept MultiLineStrings. Use ST_LineMerge to generate a LineString, or ST_Dump to extract LineStrings.

This function supports 3d and will not drop the z-index.

Enhanced: 3.7.0 - Support for curved input rings was introduced.

Examples

Single input variant.

Create a Polygon from a 2D LineString.

SELECT ST_MakePolygon('LINESTRING(75 29,77 29,77 29,75 29)');

Create a Polygon from an open LineString, using ST_StartPoint and ST_AddPoint to close it.

SELECT ST_MakePolygon(ST_AddPoint(foo.open_line, ST_StartPoint(foo.open_line)) )
FROM (
  SELECT 'LINESTRING(75 29,77 29,77 29,75 29)'::geometry As open_line) As foo;

Create a Polygon from a 3D LineString

SELECT ST_MakePolygon('LINESTRING(75.15 29.53 1,77 29 1,77.6 29.5 1,75.15 29.53 1)');

POLYGON((75.15 29.53 1,77 29 1,77.6 29.5 1,75.15 29.53 1))

010300008001000000040000009A99999999C9524048E17A14AE873D40000000000000F03F00000000004053400000000000003D40000000000000F03F66666666666653400000000000803D40000000000000F03F9A99999999C9524048E17A14AE873D40000000000000F03F

Figure

Create a Polygon from a LineString with measures

SELECT ST_MakePolygon('LINESTRINGM(75.15 29.53 1,77 29 1,77.6 29.5 2, 75.15 29.53 2)');

POLYGONM((75.15 29.53 1,77 29 1,77.6 29.5 2,75.15 29.53 2))

010300004001000000040000009A99999999C9524048E17A14AE873D40000000000000F03F00000000004053400000000000003D40000000000000F03F66666666666653400000000000803D4000000000000000409A99999999C9524048E17A14AE873D400000000000000040

Figure

Create a CurvePolygon from a CircularString shell.

SELECT ST_MakePolygon('CIRCULARSTRING(0 0,1 1,2 0,1 -1,0 0)');

CURVEPOLYGON(CIRCULARSTRING(0 0,1 1,2 0,1 -1,0 0))

010A0000000100000001080000000500000000000000000000000000000000000000000000000000F03F000000000000F03F00000000000000400000000000000000000000000000F03F000000000000F0BF00000000000000000000000000000000

Figure

Outer shell with inner holes variant.

Create a donut Polygon with an extra hole

SELECT ST_MakePolygon(
    ST_ExteriorRing(ST_Buffer(ring.line, 10)),
    ARRAY[  ST_Translate(ring.line, 1, 1),
        ST_ExteriorRing(ST_Buffer(ST_Point(20, 20), 1)) ]
    )
FROM (SELECT ST_ExteriorRing(ST_Buffer(ST_Point(10, 10), 10, 10)) AS line ) AS ring;

Create a set of province boundaries with holes representing lakes. The input is a table of province Polygons/MultiPolygons and a table of water linestrings. Lines forming lakes are determined by using ST_IsClosed. The province linework is extracted by using ST_Boundary. As required by ST_MakePolygon, the boundary is forced to be a single LineString by using ST_LineMerge. (However, note that if a province has more than one region or has islands this will produce an invalid polygon.) Using a LEFT JOIN ensures all provinces are included even if they have no lakes.

	The CASE construct is used because passing a null array into ST_MakePolygon results in a NULL return value.

SELECT p.gid, p.province_name,
  CASE
    WHEN array_agg(w.geom) IS NULL THEN p.geom
    ELSE ST_MakePolygon(
      ST_LineMerge(ST_Boundary(p.geom)),
      array_agg(w.geom)
    )
  END AS geom
FROM provinces p
LEFT JOIN waterlines w
  ON ST_Within(w.geom, p.geom)
  AND ST_IsClosed(w.geom)
GROUP BY p.gid, p.province_name, p.geom;

Another technique is to utilize a correlated subquery and the ARRAY() constructor that converts a row set to an array.

SELECT p.gid, p.province_name,
  CASE
    WHEN EXISTS (
      SELECT w.geom
      FROM waterlines w
      WHERE ST_Within(w.geom, p.geom)
      AND ST_IsClosed(w.geom)
    )
    THEN ST_MakePolygon(
      ST_LineMerge(ST_Boundary(p.geom)),
      ARRAY(
        SELECT w.geom
        FROM waterlines w
        WHERE ST_Within(w.geom, p.geom)
        AND ST_IsClosed(w.geom)
      )
    )
    ELSE p.geom
  END AS geom
FROM provinces p;

See Also

ST_BuildArea ST_Polygon