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.
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Homogeneous (uniform) collections are returned as the appropriate multi-geometry.
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Heterogeneous (mixed) collections are flattened into a single GeometryCollection.
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Collections containing a single atomic element are returned as that element.
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Atomic geometries are returned unchanged. If required, these can be converted to a multi-geometry using ST_Multi.
![[Warning]](../images/warning.png)
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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_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0))');
POINT(0 0)
Nested single-element collection converted to an atomic geometry:
SELECT ST_CollectionHomogenize('GEOMETRYCOLLECTION(MULTIPOINT((0 0)))');
POINT(0 0)
Collection converted to a multi-geometry:
SELECT ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0), POINT(1 1))');
MULTIPOINT((0 0),(1 1))
Nested heterogeneous collection flattened to a GeometryCollection:
SELECT ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0), GEOMETRYCOLLECTION( LINESTRING(1 1,2 2)))');
GEOMETRYCOLLECTION(POINT(0 0), LINESTRING(1 1,2 2))
Collection of Polygons converted to an (invalid) MultiPolygon:
SELECT 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)))');
MULTIPOLYGON(((10 50,50 50,50 10,10 10,10 50)),((90 50,90 10,50 10,50 50,90 50)))