ST_InteriorRingN - Amazon Redshift
SyntaxArgumentsReturn typeExamples

ST_InteriorRingN

ST_InteriorRingN returns a closed linestring corresponding to the interior ring of an input polygon at the index position. The dimension of the returned geometry is the same as that of the input geometry.

Syntax

ST_InteriorRingN(geom, index)

Arguments

geom

A value of data type GEOMETRY or an expression that evaluates to a GEOMETRY type.

index

A value of data type INTEGER that represents the position of a ring of a one-based index.

Return type

GEOMETRY of subtype LINESTRING.

The spatial reference system identifier (SRID) value of the returned geometry is the SRID value of the input geometry.

If geom or index is null, then null is returned.

If index is out of range, then null is returned.

If geom is not a polygon, then null is returned.

If geom is an empty polygon, then null is returned.

Examples

The following SQL returns the second ring of the polygon as a closed linestring. 

SELECT ST_AsEWKT(ST_InteriorRingN(ST_GeomFromText('POLYGON((7 9,8 7,11 6,15 8,16 6,17 7,17 10,18 12,17 14,15 15,11 15,10 13,9 12,7 9),(9 9,10 10,11 11,11 10,10 8,9 9),(12 14,15 14,13 11,12 14))'),2));

st_asewkt
-----------
 LINESTRING(12 14,15 14,13 11,12 14)