This topic describes the ST_DumpRings function. This function extracts the outer rings and inner rings of the input polygon object.
Syntax
geometry_dump[] ST_DumpRings(geometry aPolygon);Parameters
Parameter | Description |
aPolygon | The polygon object that you want to specify. |
Description
This function returns a set of geometry_dump rows of the input polygon object. Each value of a row contains the geom field and the path field.
The path field is an integer array that indicates the indexes of rings. The value 0 indicates the outer ring. A value that is greater than 0 indicates an inner ring.
The geom field represents the corresponding ring as a polygon object.
This function supports only polygon objects. The MultiPolygon objects are not supported.
This function supports 3D objects.
Examples
Results returned by using the default parameter settings:
SELECT (t.dump).path,ST_AsText((t.dump).geom) from (select ST_DumpRings('POLYGON((0 0,0 4,4 4,4 0,0 0),(1 1,2 1,2 2,1 2,1 1))'::geometry) as dump) as t;
path | st_astext
------+--------------------------------
{0} | POLYGON((0 0,0 4,4 4,4 0,0 0))
{1} | POLYGON((1 1,2 1,2 2,1 2,1 1))
(2 rows)