The SE_BoundingBox() function

The buildingfootprints table is created with the following statement. The building_id column uniquely identifies the buildings, the lot_id identifies the building's lot, and the footprint multipolygon stores the building's geometry:

CREATE TABLE buildingfootprints (building_id  integer,
                                 lot_id       integer,
                                 footprint    ST_MultiPolygon);

After the table is populated, create an R-tree index on the footprint column:

CREATE INDEX footprint_ix 
   ON buildingfootprints (footprint ST_Geometry_ops)
   USING RTREE;

Use the SE_BoundingBox() function to obtain a polygon that defines the spatial extent of all the polygons in the table:

EXECUTE FUNCTION SE_BoundingBox ('buildingfootprints', 'footprint');


(expression)  1000 POLYGON ((7 22, 38 22, 38 55, 7 55, 7 22)) 

You cannot use the SE_BoundingBox() function on a functional R-tree index. Instead, you must use the rtreeRootBB() function. The rtreeRootBB() function takes the index name and type name as arguments and returns the well-known text representation of an ST_Polygon, as shown in the following example:

CREATE TABLE xytab (x float, y float, srid int);

INSERT INTO xytab VALUES (1, 2, 0);
INSERT INTO xytab VALUES (3, 4, 0);
   
CREATE INDEX point_idx ON xytab
   (ST_Point(x,y,srid) ST_Geometry_ops) USING RTREE;

EXECUTE FUNCTION rtreeRootBB('point_idx', 'st_point');

(expression)  0 POLYGON ((1 2, 3 2, 3 4, 1 4, 1 2))