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ST_IsClosed

Tests whether a LineString or MultiLineString is closed (start point equals end point).

Syntax​

ST_IsClosed(geometry)

Parameters​

ParameterTypeDescription
geometryGeometryLineString or MultiLineString to test

Returns​

TypeDescription
BooleanTrue if geometry is closed, false otherwise

Examples​

Closed LineString (Ring)​

SELECT ST_IsClosed(ST_GeomFromText('LINESTRING(0 0, 4 0, 4 4, 0 4, 0 0)'));
-- Returns: true

Open LineString​

SELECT ST_IsClosed(ST_GeomFromText('LINESTRING(0 0, 4 0, 4 4)'));
-- Returns: false

Find Unclosed Boundaries​

SELECT id FROM boundaries
WHERE NOT ST_IsClosed(geom);

Convert to Polygon​

SELECT id, ST_GeomFromText('POLYGON((' || coords || '))')
FROM (
    SELECT id, coords FROM line_features
    WHERE ST_IsClosed(geom)
);

Notes​

  • Only applies to LineStrings and MultiLineStrings
  • For MultiLineString, all component lines must be closed
  • Points and Polygons return NULL or error
  • A closed LineString is not necessarily a valid ring (could self-intersect)

See Also​