ST_Expand
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## 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

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 on both axes, or by specifying an expansion distance for each axis. Uses double-precision. Can be used for distance queries, or to add a bounding box filter to a query to take advantage of a spatial index.

In addition to the version of ST_Expand accepting and returning a geometry, variants are provided that accept and return box2d and box3d data types.

Distances are in the units of the spatial reference system of the input.

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

Pre version 1.3, ST_Expand was used in conjunction with ST_Distance to do indexable distance queries. For example, `geom && ST_Expand('POINT(10 20)', 10) AND ST_Distance(geom, 'POINT(10 20)') < 10`. This has been replaced by the simpler and more efficient ST_DWithin function.

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

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_Buffer, ST_DWithin, ST_SRID

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