Name
ST_CollectionHomogenize — Returns the simplest representation of a geometry collection.
Synopsis
geometry ST_CollectionHomogenize(geometry collection);
Description
Given a geometry collection, returns the "simplest" representation of the contents.
Homogeneous (uniform) collections are returned as the appropriate multi-geometry.
Heterogeneous (mixed) collections are flattened into a single GeometryCollection.
Collections containing a single atomic element are returned as that element.
Atomic geometries are returned unchanged. If required, these can be converted to a multi-geometry using ST_Multi.
![[Warning]](images/warning.png) | |
This function does not ensure that the result is valid. In particular, a collection containing adjacent or overlapping Polygons will create an invalid MultiPolygon. This situation can be checked with ST_IsValid and repaired with ST_MakeValid. |
Availability: 2.0.0
Examples
Single-element collection converted to an atomic geometry
SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0))'));
st_astext
------------
POINT(0 0)
Nested single-element collection converted to an atomic geometry:
SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(MULTIPOINT((0 0)))'));
st_astext
------------
POINT(0 0)
Collection converted to a multi-geometry:
SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0),POINT(1 1))'));
st_astext
---------------------
MULTIPOINT(0 0,1 1)
Nested heterogeneous collection flattened to a GeometryCollection:
SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0), GEOMETRYCOLLECTION( LINESTRING(1 1, 2 2)))'));
st_astext
---------------------
GEOMETRYCOLLECTION(POINT(0 0),LINESTRING(1 1,2 2))
Collection of Polygons converted to an (invalid) MultiPolygon:
SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION (POLYGON ((10 50, 50 50, 50 10, 10 10, 10 50)), POLYGON ((90 50, 90 10, 50 10, 50 50, 90 50)))'));
st_astext
---------------------
MULTIPOLYGON(((10 50,50 50,50 10,10 10,10 50)),((90 50,90 10,50 10,50 50,90 50)))