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Description

Return the ’estimated’ extent of the given spatial table. The estimated is taken from the geometry column’s statistics. The currentschema will be used if not specified.

For PostgreSQL>=8.0.0 statistics are gathered by VACUUM ANALYZE and resulting extent will be about 95% of the real one.

For PostgreSQL<8.0.0 statistics are gathered by update_geometry_stats() and resulting extent will be exact.

This method supports Circular Strings and Curves

Examples

SELECT ST_Estimated_extent(’ny’, ’edges’, ’the_geom’);--result--BOX(-8877653 4912316,-8010225.5 5589284)

SELECT ST_Estimated_Extent(’feature_poly’, ’the_geom’);--result--BOX(-124.659652709961 24.6830825805664,-67.7798080444336 49.0012092590332)

See Also

ST_Extent

7.12.5 ST_Expand

Name

ST_Expand – Returns bounding box expanded in all directions from the bounding box of the input geometry. Uses double-precision

Synopsis

geometry 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);

Description

This 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 SRID

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NotePre 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.

Examples

NoteExamples 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 110701,2312892 ←↩

110714)’, 2163),10) As box2d);st_expand

------------------------------------BOX(2312882 110666,2312990 110724)

--10 meter expanded 3d box of a 3d boxSELECT 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 geometrySELECT 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

7.12.6 ST_Extent

Name

ST_Extent – an aggregate function that returns the bounding box that bounds rows of geometries.