PostGIS
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.
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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
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--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))