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PostGIS 1.5.8 Manual252 / 3107.12.5 ST_ExpandST_Expand — Returns bounding box expanded in all directions from the bounding box of the input geometry. Uses doubleprecisionSynopsisgeometry ST_Expand(geometry g1, float units_to_expand);box2d ST_Expand(box2d g1, float units_to_expand);box3d ST_Expand(box3d g1, float units_to_expand);DescriptionThis function returns a bounding box expanded in all directions from the bounding box of the input geometry, by an amountspecified in the second argument. Uses double-precision. Very useful for distance() queries, or bounding box queries to add anindex filter to the query.There are 3 variants of this. The one that takes a geometry will return a POLYGON geometry representation of the bounding boxand is the most commonly used variant.ST_Expand is similar in concept to ST_Buffer except while buffer expands the geometry in all directions, ST_Expand expandsthe bounding box an x,y,z unit amount.Units are in the units of the spatial reference system in use denoted by the SRIDNotePre 1.3, ST_Expand was used in conjunction with distance to do indexable queries. Something ofthe form the_geom && ST_Expand(’POINT(10 20)’, 10) AND ST_Distance(the_geom, ’PO-INT(10 20)’) < 10 Post 1.2, this was replaced with the easier ST_DWithin construct.NoteBounding boxes of all geometries are currently 2-d even if they are 3-dimensional geometries.NoteAvailability: 1.5.0 behavior changed to output double precision instead of float4 coordinates.ExamplesNoteExamples below use US National Atlas Equal Area (SRID=2163) which is a meter projection--10 meter expanded box around bbox of a linestringSELECT CAST(ST_Expand(ST_GeomFromText(’LINESTRING(2312980 110676,2312923 110701,2312892110714)’, 2163),10) As box2d);st_expand------------------------------------←↪