PostGIS
Description
Returns the Nth interior ring (hole) of a POLYGON geometry as a LINESTRING. The index starts at 1. Returns NULL if the geometry is not a polygon or the index is out of range.
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[.inlinemediaobject]
This method implements the
OGC Simple Features
Implementation Specification for SQL 1.1.
This
method implements the SQL/MM specification.
SQL-MM 3: 8.2.6, 8.3.5
This
function supports 3d and will not drop the z-index.
Examples
SELECT ST_AsText(ST_InteriorRingN(geom, 1)) As geom
FROM (SELECT ST_BuildArea(
ST_Collect(ST_Buffer(ST_Point(1,2), 20,3),
ST_Buffer(ST_Point(1, 2), 10,3))) As geom
) as foo;