Name

ST_Expand — Returns a bounding box expanded from another bounding box or a geometry.

Synopsis

geometry ST_Expand(geometry geom, float units_to_expand);

geometry ST_Expand(geometry geom, float dx, float dy, float dz=0, float dm=0);

box2d ST_Expand(box2d box, float units_to_expand);

box2d ST_Expand(box2d box, float dx, float dy);

box3d ST_Expand(box3d box, float units_to_expand);

box3d ST_Expand(box3d box, float dx, float dy, float dz=0);

Description

This function returns a bounding box expanded from the bounding box of the input, either by specifying a single distance with which the box should be expanded in all directions, or by specifying an expansion distance for each direction. Uses double-precision. Can be very useful for distance queries, or to add a bounding box filter to a query to take advantage of a spatial index.

In addition to the geometry version of ST_Expand, which is the most commonly used, variants are provided that accept and produce internal BOX2D and BOX3D data types.

ST_Expand is similar in concept to ST_Buffer, except while buffer expands the geometry in all directions, ST_Expand expands the bounding box along each axis.

Units are in the units of the spatial reference system in use denoted by the SRID.

[Note]

Pre version 1.3, ST_Expand was used in conjunction with ST_Distance to do indexable distance queries. For example, the_geom && ST_Expand('POINT(10 20)', 10) AND ST_Distance(the_geom, 'POINT(10 20)') < 10. This has been replaced by the easier ST_DWithin construct.

[Note]

Availability: 1.5.0 behavior changed to output double precision instead of float4 coordinates.

Enhanced: 2.0.0 support for Polyhedral surfaces, Triangles and TIN was introduced.

Enhanced: 2.3.0 support was added to expand a box by different amounts in different dimensions.

This function supports Polyhedral surfaces.

This function supports Triangles and Triangulated Irregular Network Surfaces (TIN).

Examples

[Note]

Examples below use US National Atlas Equal Area (SRID=2163) which is a meter projection

		
--10 meter expanded box around bbox of a linestring
SELECT CAST(ST_Expand(ST_GeomFromText('LINESTRING(2312980 110676,2312923 110701,2312892 110714)', 2163),10) As box2d);
					 st_expand
------------------------------------
 BOX(2312882 110666,2312990 110724)

--10 meter expanded 3D box of a 3D box
SELECT ST_Expand(CAST('BOX3D(778783 2951741 1,794875 2970042.61545891 10)' As box3d),10)
							  st_expand
-----------------------------------------------------
 BOX3D(778773 2951731 -9,794885 2970052.61545891 20)

 --10 meter geometry astext rep of a expand box around a point geometry
 SELECT ST_AsEWKT(ST_Expand(ST_GeomFromEWKT('SRID=2163;POINT(2312980 110676)'),10));
											st_asewkt
-------------------------------------------------------------------------------------------------
 SRID=2163;POLYGON((2312970 110666,2312970 110686,2312990 110686,2312990 110666,2312970 110666))

		

See Also

ST_AsEWKT, ST_Buffer, ST_DWithin, ST_GeomFromEWKT, ST_GeomFromText, ST_SRID