ST_IsRing

Description

Returns TRUE if this LINESTRING is both ST_IsClosed ( ST_StartPoint( g ) ~= ST_Endpoint( g ) ) and ST_IsSimple (does not self intersect).

This method implements the OGC Simple Features Implementation Specification for SQL 1.1.

2.1.5.1

This method implements the SQL/MM specification.

SQL-MM 3: 7.1.6

	SQL-MM defines the result of ST_IsRing( NULL ) to be 0, while PostGIS returns NULL .

Examples

SELECT ST_IsRing(geom), ST_IsClosed(geom), ST_IsSimple(geom)
FROM (SELECT 'LINESTRING(0 0, 0 1, 1 1, 1 0, 0 0)'::geometry AS geom) AS foo;
 st_isring | st_isclosed | st_issimple
-----------+-------------+-------------
 t         | t           | t
(1 row)

SELECT ST_IsRing(geom), ST_IsClosed(geom), ST_IsSimple(geom)
FROM (SELECT 'LINESTRING(0 0, 0 1, 1 0, 1 1, 0 0)'::geometry AS geom) AS foo;
 st_isring | st_isclosed | st_issimple
-----------+-------------+-------------
 f         | t           | f
(1 row)

See Also

ST_IsClosed , ST_IsSimple , ST_StartPoint , ST_EndPoint