PostGIS
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
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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)