ST_IsRing
Prev | 8.4. Geometry Accessors | Next

## Name

ST_IsRing — Tests if a LineString is closed and simple.

## Synopsis

`boolean ST_IsRing(`geometry g`)`;

## 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

Prev | Up | Next
ST_IsPolygonCW | Home | ST_IsSimple