A `GEOMETRYCOLLECTION` is a collection of heterogeneous spatial objects, such as Points, LineStrings, Polygons, or other `GEOMETRYCOLLECTION`s. It provides a way of referring to a group of spatial objects as one "thing" so that you can operate on it/them more conveniently using various SQL functions.

You can also store a `GEOMETRYCOLLECTION` with the following additional dimensions:

• A third dimension coordinate `Z` (`GEOMETRYCOLLECTIONZ`).
• A measure coordinate `M` (`GEOMETRYCOLLECTIONM`).
• Both a third dimension and a measure coordinate (`GEOMETRYCOLLECTIONZM`).

The `Z` and `M` dimensions can be accessed or modified using a number of built-in functions, including:

• `ST_Z`
• `ST_M`
• `ST_Affine`
• `ST_Zmflag`
• `ST_MakePoint`
• `ST_MakePointM`
• `ST_Force3D`
• `ST_Force3DZ`
• `ST_Force3DM`
• `ST_Force4D`
• `ST_Snap`
• `ST_SnapToGrid`
• `ST_RotateZ`
• `ST_AddMeasure`

Note that CockroachDB's spatial indexing is still based on the 2D coordinate system. This means that:

• The Z/M dimension is not index accelerated when using spatial predicates.
• Some spatial functions ignore the Z/M dimension, with transformations discarding the Z/M value.

## Examples

A GeometryCollection can be created from SQL by calling the `st_geomfromtext` function on a GeometryCollection definition expressed in the Well Known Text (WKT) format as shown below.

``````SELECT ST_GeomFromText('GEOMETRYCOLLECTION(POINT(0 0), LINESTRING(0 0, 1440 900), POLYGON((0 0, 0 1024, 1024 1024, 1024 0, 0 0)))');
``````
``````                                                                                                                                                              st_geomfromtext
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0107000000030000000101000000000000000000000000000000000000000102000000020000000000000000000000000000000000000000000000008096400000000000208C40010300000001000000050000000000000000000000000000000000000000000000000000000000000000009040000000000000904000000000000090400000000000009040000000000000000000000000000000000000000000000000
(1 row)
``````