ST_InteriorRingN

Returns the N-th interior ring of a Polygon. This function retrieves a specific inner hole of the polygon as a LineString.

Syntax

ST_InteriorRingN(poly,N)
InteriorRingN(poly,N)

Description

Returns the N-th interior ring for the Polygon value poly as a LineString. Rings are numbered beginning with 1.

ST_InteriorRingN() and InteriorRingN() are synonyms.

Examples

SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';

SELECT AsText(InteriorRingN(GeomFromText(@poly),1));
+----------------------------------------------+
| AsText(InteriorRingN(GeomFromText(@poly),1)) |
+----------------------------------------------+
| LINESTRING(1 1,1 2,2 2,2 1,1 1)              |
+----------------------------------------------+

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