PostGIS

ST_DumpRings
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ST_DumpRings

7.4. Geometry Accessors

Name

ST_DumpRings — Returns a set of geometry_dump rows for the exterior and interior rings of a Polygon.

Synopsis

geometry_dump[] +`*`+ST_DumpRings*(`geometry `a_polygon`)`;

Description

A set-returning function (SRF) that extracts the rings of a polygon. It returns a set of geometry_dump rows, each containing a geometry (`geomfield) and an array of integers (path` field).

The `geom field contains each ring as a POLYGON. The path` field is an integer array of length 1 containing the polygon ring index. The exterior ring (shell) has index 0. The interior rings (holes) have indices of 1 and higher.

This only works for POLYGON geometries. It does not work for MULTIPOLYGONS

Availability: PostGIS 1.1.3. Requires PostgreSQL 7.3 or higher.

check This function supports 3d and will not drop the z-index.

Examples

General form of query.

SELECT polyTable.field1, polyTable.field1,
      (ST_DumpRings(polyTable.geom)).geom As geom
FROM polyTable;

A polygon with a single hole.

SELECT path, ST_AsEWKT(geom) As geom
    FROM ST_DumpRings(
        ST_GeomFromEWKT('POLYGON((-8149064 5133092 1,-8149064 5132986 1,-8148996 5132839 1,-8148972 5132767 1,-8148958 5132508 1,-8148941 5132466 1,-8148924 5132394 1,
        -8148903 5132210 1,-8148930 5131967 1,-8148992 5131978 1,-8149237 5132093 1,-8149404 5132211 1,-8149647 5132310 1,-8149757 5132394 1,
        -8150305 5132788 1,-8149064 5133092 1),
        (-8149362 5132394 1,-8149446 5132501 1,-8149548 5132597 1,-8149695 5132675 1,-8149362 5132394 1))')
        )  as foo;
 path |                                            geom
----------------------------------------------------------------------------------------------------------------
  {0} | POLYGON((-8149064 5133092 1,-8149064 5132986 1,-8148996 5132839 1,-8148972 5132767 1,-8148958 5132508 1,
      |          -8148941 5132466 1,-8148924 5132394 1,
      |          -8148903 5132210 1,-8148930 5131967 1,
      |          -8148992 5131978 1,-8149237 5132093 1,
      |          -8149404 5132211 1,-8149647 5132310 1,-8149757 5132394 1,-8150305 5132788 1,-8149064 5133092 1))
  {1} | POLYGON((-8149362 5132394 1,-8149446 5132501 1,
      |          -8149548 5132597 1,-8149695 5132675 1,-8149362 5132394 1))

PostGIS

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Examples

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