ST_Envelope function

The ST_Envelope function takes a geometry as an input parameter and returns an envelope around the geometry. The envelope is a rectangle that is represented as a polygon.

If the specified geometry is a point, a horizontal linestring, or a vertical linestring, then a rectangle, which is slightly larger than the specified geometry, is returned. Otherwise, the minimum bounding rectangle of the geometry is returned as the envelope. If the specified geometry is null or is empty, then null is returned. To return the exact minimum bounding rectangle for all geometries, use the function ST_MBR.

Syntax

Parameter

geometry: A value of type ST_Geometry that represents the geometry to return the envelope for.

Return type

ST_Polygon

Example

In the following examples, the lines of results have been reformatted for readability. The spacing in your results will vary according to your online display.

This example creates several geometries and then determines their envelopes. For the non-empty point and the linestring (which is horizontal), the envelope is a rectangle that is slightly larger than the geometry.


CREATE TABLE sample_geoms (id INTEGER, geometry ST_Geometry)

INSERT INTO sample_geoms VALUES
    (1, ST_Geometry('point EMPTY',0))

INSERT INTO sample_geoms VALUES
    (2, ST_Geometry('point zm (10 10 16 30)' ,0))

INSERT INTO sample_geoms VALUES
    (3, ST_Geometry('multipoint m (10 10 5, 50 10 6, 10 30 8)' ,0))

INSERT INTO sample_geoms VALUES
    (4, ST_Geometry('linestring (10 10, 20 10)',0))

INSERT INTO sample_geoms VALUES
    (5, ST_Geometry('polygon((40 120, 90 120, 90 150, 40 150, 40 120))',0))


SELECT id, CAST(ST_AsText(ST_Envelope(geometry)) as VARCHAR(160))  Envelope
FROM sample_geoms

Results:


ID          ENVELOPE
----------- ---------------------------------------------------------------
          1 -                                                                                                                                                       
          2 POLYGON ((9 9, 11 9, 11 11, 9 11, 9 9))                                                                                                                 
          3 POLYGON ((10 10, 50 10, 50 30, 10 30, 10 10))                                                                                                           
          4 POLYGON ((10 9, 20 9, 20 11, 10 11, 10 9))                                                                                                              
          5 POLYGON ((40 120, 90 120, 90 150, 40 150, 40 120))