ST_Envelope
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## Name

ST_Envelope — Returns a geometry representing the bounding box of a geometry.

## Synopsis

`geometry ST_Envelope(`geometry g1`)`;

## Description

Returns the double-precision (float8) minimum bounding box for the supplied geometry, as a geometry. The polygon is defined by the corner points of the bounding box ((`MINX`, `MINY`), (`MINX`, `MAXY`), (`MAXX`, `MAXY`), (`MAXX`, `MINY`), (`MINX`, `MINY`)). (PostGIS will add a `ZMIN`/`ZMAX` coordinate as well).

Degenerate cases (vertical lines, points) will return a geometry of lower dimension than `POLYGON`, ie. `POINT` or `LINESTRING`.

Availability: 1.5.0 behavior changed to output double precision instead of float4

This method implements the OGC Simple Features Implementation Specification for SQL 1.1. s2.1.1.1

This method implements the SQL/MM specification. SQL-MM 3: 5.1.19

## Examples

    SELECT ST_AsText(ST_Envelope('POINT(1 3)'::geometry));
     st_astext
    ------------
     POINT(1 3)
    (1 row)

    SELECT ST_AsText(ST_Envelope('LINESTRING(0 0, 1 3)'::geometry));
    		   st_astext
    --------------------------------
     POLYGON((0 0,0 3,1 3,1 0,0 0))
    (1 row)

    SELECT ST_AsText(ST_Envelope('POLYGON((0 0, 0 1, 1.0000001 1, 1.0000001 0, 0 0))'::geometry));
    						  st_astext
    --------------------------------------------------------------
     POLYGON((0 0,0 1,1.00000011920929 1,1.00000011920929 0,0 0))
    (1 row)
    SELECT ST_AsText(ST_Envelope('POLYGON((0 0, 0 1, 1.0000000001 1, 1.0000000001 0, 0 0))'::geometry));
    						  st_astext
    --------------------------------------------------------------
     POLYGON((0 0,0 1,1.00000011920929 1,1.00000011920929 0,0 0))
    (1 row)

    SELECT Box3D(geom), Box2D(geom), ST_AsText(ST_Envelope(geom)) As envelopewkt
    	FROM (SELECT 'POLYGON((0 0, 0 1000012333334.34545678, 1.0000001 1, 1.0000001 0, 0 0))'::geometry As geom) As foo;

Envelope of a point and linestring.

    SELECT ST_AsText(ST_Envelope(
    		ST_Collect(
    			ST_GeomFromText('LINESTRING(55 75,125 150)'),
    				ST_Point(20, 80))
    				)) As wktenv;
    wktenv
    -----------
    POLYGON((20 75,20 150,125 150,125 75,20 75))

## See Also

Box2D, Box3D, ST_OrientedEnvelope

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