## Name

ST_Extent3D — an aggregate function that returns the box3D bounding box that bounds rows of geometries.

## Synopsis

`box3d ST_Extent3D(`geometry set geomfield`)`;

## Description

ST_Extent3D returns a box3d (includes Z coordinate) bounding box that encloses a set of geometries. The ST_Extent3D function is an "aggregate" function in the terminology of SQL. That means that it operates on lists of data, in the same way the SUM() and AVG() functions do.

Since it returns a bounding box, the spatial Units are in the units of the spatial reference system in use denoted by the SRID

 Since ST_Extent3D returns a bounding box, the SRID meta-data is lost. Use ST_SetSRID to force it back into a geometry with SRID meta data. The coordinates are in the units of the spatial ref of the orginal geometries.

This function supports 3d and will not drop the z-index.

This method supports Circular Strings and Curves

## Examples

```SELECT ST_Extent3D(foo.the_geom) As b3extent
FROM (SELECT ST_MakePoint(x,y,z) As the_geom
FROM generate_series(1,3) As x
CROSS JOIN generate_series(1,2) As y
CROSS JOIN generate_series(0,2) As Z) As foo;
b3extent
--------------------
BOX3D(1 1 0,3 2 2)

--Get the extent of various elevated circular strings
SELECT ST_Extent3D(foo.the_geom) As b3extent
FROM (SELECT ST_Translate(ST_Force_3DZ(ST_LineToCurve(ST_Buffer(ST_MakePoint(x,y),1))),0,0,z) As the_geom
FROM generate_series(1,3) As x
CROSS JOIN generate_series(1,2) As y
CROSS JOIN generate_series(0,2) As Z) As foo;

b3extent
--------------------
BOX3D(1 0 0,4 2 2)
```