ST_Polygonize-PolarDB(PolarDB)-阿里云帮助中心

ST_Polygonize is an aggregate function that builds polygons from a set of input lines. It returns a GeometryCollection containing all polygons formed by the constituent lines of the input geometries.

Syntax

geometry  ST_Polygonize(geometry set  geomField);
geometry  ST_Polygonize(geometry[]  geomArray);

Parameters

Parameter	Description
geomField	The geometry fields in the dataset.
geomArray	An array of geometry objects.

Usage notes

Input lines must be correctly noded. All intersection points must be inserted as vertices before polygonizing.
`GeometryCollection` output. Most third-party tools do not support GeometryCollection objects. Use ST_Dump to expand the result into individual polygon rows.

Examples

Build polygons from an array of lines

The following example builds a polygon from four line segments that form a closed square.

SELECT ST_AsText(
  ST_Polygonize(
    ARRAY[
      'LINESTRING(0 0,0 1)'::geometry,
      'LINESTRING(0 1,1 1)'::geometry,
      'LINESTRING(1 1,1 0)'::geometry,
      'LINESTRING(0 0,1 0)'::geometry
    ]
  )
);

Output:

                     st_astext
----------------------------------------------------
 GEOMETRYCOLLECTION(POLYGON((0 0,0 1,1 1,1 0,0 0)))
(1 row)

What's next

ST_Dump: Expand a GeometryCollection into individual geometry rows.