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ST_IsRing

Tests whether a LineString is a ring - closed and simple (no self-intersections).

Syntax​

ST_IsRing(geometry)

Parameters​

ParameterTypeDescription
geometryGeometryLineString to test

Returns​

TypeDescription
BooleanTrue if geometry is a ring, false otherwise

Examples​

Valid Ring​

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

Not Closed (Not a Ring)​

SELECT ST_IsRing(ST_GeomFromText('LINESTRING(0 0, 4 0, 4 4)'));
-- Returns: false (not closed)

Self-Intersecting (Not a Ring)​

SELECT ST_IsRing(ST_GeomFromText('LINESTRING(0 0, 2 2, 2 0, 0 2, 0 0)'));
-- Returns: false (self-intersects)

Find Valid Polygon Candidates​

SELECT id FROM line_features
WHERE ST_IsRing(geom);

Notes​

  • A ring is a LineString that is both closed AND simple
  • ST_IsRing = ST_IsClosed AND ST_IsSimple
  • Rings can be used to construct valid polygons
  • Only applies to LineStrings

See Also​