Viewing github.com/django/django-stable-4.1.x/docs/ref/contrib/gis/functions.txt

```
=============================
```
```
Geographic Database Functions
```
```
=============================
```

.. module:: django.contrib.gis.db.models.functions

    :synopsis: Geographic Database Functions

The functions documented on this page allow users to access geographic database

functions to be used in annotations, aggregations, or filters in Django.

```
Example::
```

    >>> from django.contrib.gis.db.models.functions import Length

    >>> Track.objects.annotate(length=Length('line')).filter(length__gt=100)

Not all backends support all functions, so refer to the documentation of each

function to see if your database backend supports the function you want to use.

If you call a geographic function on a backend that doesn't support it, you'll

get a ``NotImplementedError`` exception.

```
Function's summary:
```

=========================  ========================  ======================  =======================  ==================  =====================

Measurement                Relationships             Operations              Editors                  Output format       Miscellaneous

=========================  ========================  ======================  =======================  ==================  =====================

:class:`Area`              :class:`Azimuth`          :class:`Difference`     :class:`ForcePolygonCW`  :class:`AsGeoJSON`  :class:`IsValid`

:class:`Distance`          :class:`BoundingCircle`   :class:`Intersection`   :class:`MakeValid`       :class:`AsGML`      :class:`MemSize`

:class:`GeometryDistance`  :class:`Centroid`         :class:`SymDifference`  :class:`Reverse`         :class:`AsKML`      :class:`NumGeometries`

:class:`Length`            :class:`Envelope`         :class:`Union`          :class:`Scale`           :class:`AsSVG`      :class:`NumPoints`

:class:`Perimeter`         :class:`LineLocatePoint`                          :class:`SnapToGrid`      :class:`AsWKB`

..                         :class:`PointOnSurface`                           :class:`Transform`       :class:`AsWKT`

..                                                                           :class:`Translate`       :class:`GeoHash`

=========================  ========================  ======================  =======================  ==================  =====================

```
``Area``
```
```
========
```
```
.. class:: Area(expression, **extra)
```
```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-polygon-property-functions.html#function_st-area>`_,

Oracle, `PostGIS <https://postgis.net/docs/ST_Area.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns the area of the

field as an :class:`~django.contrib.gis.measure.Area` measure.

MySQL and SpatiaLite without LWGEOM/RTTOPO don't support area calculations on

```
geographic SRSes.
```
```
``AsGeoJSON``
```
```
=============
```

.. class:: AsGeoJSON(expression, bbox=False, crs=False, precision=8, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-geojson-functions.html#function_st-asgeojson>`__ (≥ 5.7.5),

Oracle, `PostGIS <https://postgis.net/docs/ST_AsGeoJSON.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns a `GeoJSON

<https://geojson.org/>`_ representation of the geometry. Note that the result

is not a complete GeoJSON structure but only the ``geometry`` key content of a

GeoJSON structure. See also :doc:`/ref/contrib/gis/serializers`.

```
Example::
```

    >>> City.objects.annotate(json=AsGeoJSON('point')).get(name='Chicago').json

    {"type":"Point","coordinates":[-87.65018,41.85039]}

=====================  =====================================================

```
Keyword Argument       Description
```

=====================  =====================================================

``bbox``               Set this to ``True`` if you want the bounding box

                       to be included in the returned GeoJSON. Ignored on

```
                       Oracle.
```

``crs``                Set this to ``True`` if you want the coordinate

                       reference system to be included in the returned

                       GeoJSON. Ignored on MySQL and Oracle.

``precision``          It may be used to specify the number of significant

                       digits for the coordinates in the GeoJSON

                       representation -- the default value is 8. Ignored on

```
                       Oracle.
```

=====================  =====================================================

```
``AsGML``
```
```
=========
```

.. class:: AsGML(expression, version=2, precision=8, **extra)

*Availability*: Oracle, `PostGIS <https://postgis.net/docs/ST_AsGML.html>`__,

```
SpatiaLite
```

Accepts a single geographic field or expression and returns a `Geographic Markup

Language (GML)`__ representation of the geometry.

```
Example::
```

    >>> qs = Zipcode.objects.annotate(gml=AsGML('poly'))

```
    >>> print(qs[0].gml)
```

    <gml:Polygon srsName="EPSG:4326"><gml:OuterBoundaryIs>-147.78711,70.245363 ...

    -147.78711,70.245363</gml:OuterBoundaryIs></gml:Polygon>

=====================  =====================================================

```
Keyword Argument       Description
```

=====================  =====================================================

``precision``          Specifies the number of significant digits for the

                       coordinates in the GML representation -- the default

                       value is 8. Ignored on Oracle.

``version``            Specifies the GML version to use: 2 (default) or 3.

=====================  =====================================================

__ https://en.wikipedia.org/wiki/Geography_Markup_Language

```
``AsKML``
```
```
=========
```

.. class:: AsKML(expression, precision=8, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_AsKML.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns a `Keyhole Markup

Language (KML)`__ representation of the geometry.

```
Example::
```

    >>> qs = Zipcode.objects.annotate(kml=AsKML('poly'))

```
    >>> print(qs[0].kml)
```

    <Polygon><outerBoundaryIs><LinearRing><coordinates>-103.04135,36.217596,0 ...

    -103.04135,36.217596,0</coordinates></LinearRing></outerBoundaryIs></Polygon>

=====================  =====================================================

```
Keyword Argument       Description
```

=====================  =====================================================

``precision``          This keyword may be used to specify the number of

                       significant digits for the coordinates in the KML

                       representation -- the default value is 8.

=====================  =====================================================

__ https://developers.google.com/kml/documentation/

```
``AsSVG``
```
```
=========
```

.. class:: AsSVG(expression, relative=False, precision=8, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_AsSVG.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns a `Scalable Vector

Graphics (SVG)`__ representation of the geometry.

=====================  =====================================================

```
Keyword Argument       Description
```

=====================  =====================================================

``relative``           If set to ``True``, the path data will be implemented

                       in terms of relative moves. Defaults to ``False``,

                       meaning that absolute moves are used instead.

``precision``          This keyword may be used to specify the number of

                       significant digits for the coordinates in the SVG

                       representation -- the default value is 8.

=====================  =====================================================

```
__ https://www.w3.org/Graphics/SVG/
```
```
``AsWKB``
```
```
=========
```
```
.. class:: AsWKB(expression, **extra)
```
```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-format-conversion-functions.html#function_st-asbinary>`__,

Oracle, `PostGIS <https://postgis.net/docs/ST_AsBinary.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns a `Well-known

binary (WKB)`__ representation of the geometry.

```
Example::
```

    >>> bytes(City.objects.annotate(wkb=AsWKB('point')).get(name='Chelyabinsk').wkb)

    b'\x01\x01\x00\x00\x00]3\xf9f\x9b\x91K@\x00X\x1d9\xd2\xb9N@'

__ https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry#Well-known_binary

```
``AsWKT``
```
```
=========
```
```
.. class:: AsWKT(expression, **extra)
```
```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-format-conversion-functions.html#function_st-astext>`__,

Oracle, `PostGIS <https://postgis.net/docs/ST_AsText.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns a `Well-known text

(WKT)`__ representation of the geometry.

```
Example::
```

    >>> City.objects.annotate(wkt=AsWKT('point')).get(name='Chelyabinsk').wkt

```
    'POINT (55.137555 61.451728)'
```

__ https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry

```
``Azimuth``
```
```
===========
```

.. class:: Azimuth(point_a, point_b, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_Azimuth.html>`__,

```
SpatiaLite (LWGEOM/RTTOPO)
```

Returns the azimuth in radians of the segment defined by the given point

geometries, or ``None`` if the two points are coincident. The azimuth is angle

referenced from north and is positive clockwise: north = ``0``; east = ``π/2``;

```
south = ``π``; west = ``3π/2``.
```
```
``BoundingCircle``
```
```
==================
```

.. class:: BoundingCircle(expression, num_seg=48, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_MinimumBoundingCircle.html>`__,

`Oracle <https://docs.oracle.com/en/database/oracle/oracle-database/21/spatl/

SDO_GEOM-reference.html#GUID-82A61626-BB64-4793-B53D-A0DBEC91831A>`_

Accepts a single geographic field or expression and returns the smallest circle

polygon that can fully contain the geometry.

The ``num_seg`` parameter is used only on PostGIS.

```
``Centroid``
```
```
============
```

.. class:: Centroid(expression, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-polygon-property-functions.html#function_st-centroid>`__,

`PostGIS <https://postgis.net/docs/ST_Centroid.html>`__, Oracle, SpatiaLite

Accepts a single geographic field or expression and returns the ``centroid``

```
value of the geometry.
```
```
``Difference``
```
```
==============
```

.. class:: Difference(expr1, expr2, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-operator-functions.html#function_st-difference>`__,

`PostGIS <https://postgis.net/docs/ST_Difference.html>`__, Oracle, SpatiaLite

Accepts two geographic fields or expressions and returns the geometric

difference, that is the part of geometry A that does not intersect with

```
geometry B.
```
```
``Distance``
```
```
============
```

.. class:: Distance(expr1, expr2, spheroid=None, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-relation-functions-object-shapes.html#function_st-distance>`__,

`PostGIS <https://postgis.net/docs/ST_Distance.html>`__, Oracle, SpatiaLite

Accepts two geographic fields or expressions and returns the distance between

them, as a :class:`~django.contrib.gis.measure.Distance` object. On MySQL, a raw

float value is returned when the coordinates are geodetic.

On backends that support distance calculation on geodetic coordinates, the

proper backend function is automatically chosen depending on the SRID value of

the geometries (e.g. `ST_DistanceSphere

<https://postgis.net/docs/ST_DistanceSphere.html>`__ on PostGIS).

When distances are calculated with geodetic (angular) coordinates, as is the

case with the default WGS84 (4326) SRID, you can set the ``spheroid`` keyword

argument to decide if the calculation should be based on a simple sphere (less

accurate, less resource-intensive) or on a spheroid (more accurate, more

```
resource-intensive).
```

In the following example, the distance from the city of Hobart to every other

:class:`~django.contrib.gis.db.models.PointField` in the ``AustraliaCity``

```
queryset is calculated::
```

    >>> from django.contrib.gis.db.models.functions import Distance

    >>> pnt = AustraliaCity.objects.get(name='Hobart').point

    >>> for city in AustraliaCity.objects.annotate(distance=Distance('point', pnt)):

    ...     print(city.name, city.distance)

```
    Wollongong 990071.220408 m
```
```
    Shellharbour 972804.613941 m
```
```
    Thirroul 1002334.36351 m
```
```
    ...
```
```
.. note::
```

    Because the ``distance`` attribute is a

    :class:`~django.contrib.gis.measure.Distance` object, you can easily express

    the value in the units of your choice. For example, ``city.distance.mi`` is

    the distance value in miles and ``city.distance.km`` is the distance value

    in kilometers. See :doc:`measure` for usage details and the list of

```
    :ref:`supported_units`.
```
```
``Envelope``
```
```
============
```

.. class:: Envelope(expression, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-general-property-functions.html#function_st-envelope>`__,

`Oracle <https://docs.oracle.com/en/database/oracle/oracle-database/21/spatl/

spatial-operators-reference.html#GUID-ACED800F-3435-44AA-9606-D40934A23ED0>`__,

`PostGIS <https://postgis.net/docs/ST_Envelope.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns the geometry

representing the bounding box of the geometry.

```
``ForcePolygonCW``
```
```
==================
```

.. class:: ForcePolygonCW(expression, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_ForcePolygonCW.html>`__,

```
SpatiaLite
```

Accepts a single geographic field or expression and returns a modified version

of the polygon/multipolygon in which all exterior rings are oriented clockwise

and all interior rings are oriented counterclockwise. Non-polygonal geometries

```
are returned unchanged.
```
```
``GeoHash``
```
```
===========
```

.. class:: GeoHash(expression, precision=None, **extra)

```
*Availability*: `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-geohash-functions.html#function_st-geohash>`__ (≥ 5.7.5),

`PostGIS <https://postgis.net/docs/ST_GeoHash.html>`__, SpatiaLite

```
(LWGEOM/RTTOPO)
```

Accepts a single geographic field or expression and returns a `GeoHash`__

```
representation of the geometry.
```

The ``precision`` keyword argument controls the number of characters in the

```
result.
```

__ https://en.wikipedia.org/wiki/Geohash

```
``GeometryDistance``
```
```
====================
```

.. class:: GeometryDistance(expr1, expr2, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/geometry_distance_knn.html>`__

Accepts two geographic fields or expressions and returns the distance between

them. When used in an :meth:`~django.db.models.query.QuerySet.order_by` clause,

it provides index-assisted nearest-neighbor result sets.

```
``Intersection``
```
```
================
```

.. class:: Intersection(expr1, expr2, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-operator-functions.html#function_st-intersection>`__,

`PostGIS <https://postgis.net/docs/ST_Intersection.html>`__, Oracle, SpatiaLite

Accepts two geographic fields or expressions and returns the geometric

```
intersection between them.
```
```
``IsValid``
```
```
===========
```
```
.. class:: IsValid(expr)
```
```
*Availability*: `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-convenience-functions.html#function_st-isvalid>`__ (≥ 5.7.5),

`PostGIS <https://postgis.net/docs/ST_IsValid.html>`__, Oracle, SpatiaLite

Accepts a geographic field or expression and tests if the value is well formed.

Returns ``True`` if its value is a valid geometry and ``False`` otherwise.

```
``Length``
```
```
==========
```

.. class:: Length(expression, spheroid=True, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-linestring-property-functions.html#function_st-length>`__,

Oracle, `PostGIS <https://postgis.net/docs/ST_Length.html>`__, SpatiaLite

Accepts a single geographic linestring or multilinestring field or expression

and returns its length as a :class:`~django.contrib.gis.measure.Distance`

```
measure.
```

On PostGIS and SpatiaLite, when the coordinates are geodetic (angular), you can

specify if the calculation should be based on a simple sphere (less

accurate, less resource-intensive) or on a spheroid (more accurate, more

resource-intensive) with the ``spheroid`` keyword argument.

MySQL doesn't support length calculations on geographic SRSes.

```
``LineLocatePoint``
```
```
===================
```

.. class:: LineLocatePoint(linestring, point, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_LineLocatePoint.html>`__,

```
SpatiaLite
```

Returns a float between 0 and 1 representing the location of the closest point on

``linestring`` to the given ``point``, as a fraction of the 2D line length.

```
``MakeValid``
```
```
=============
```
```
.. class:: MakeValid(expr)
```

*Availability*: `PostGIS <https://postgis.net/docs/ST_MakeValid.html>`__,

```
SpatiaLite (LWGEOM/RTTOPO)
```

Accepts a geographic field or expression and attempts to convert the value into

a valid geometry without losing any of the input vertices. Geometries that are

already valid are returned without changes. Simple polygons might become a

multipolygon and the result might be of lower dimension than the input.

```
``MemSize``
```
```
===========
```

.. class:: MemSize(expression, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_MemSize.html>`__

Accepts a single geographic field or expression and returns the memory size

(number of bytes) that the geometry field takes.

```
``NumGeometries``
```
```
=================
```

.. class:: NumGeometries(expression, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-geometrycollection-property-functions.html#function_st-numgeometries>`__,

`PostGIS <https://postgis.net/docs/ST_NumGeometries.html>`__, Oracle,

```
SpatiaLite
```

Accepts a single geographic field or expression and returns the number of

geometries if the geometry field is a collection (e.g., a ``GEOMETRYCOLLECTION``

or ``MULTI*`` field). Returns 1 for single geometries.

On MySQL, returns ``None`` for single geometries.

```
``NumPoints``
```
```
=============
```

.. class:: NumPoints(expression, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/gis-linestring-property-functions.html#function_st-numpoints>`__,

`PostGIS <https://postgis.net/docs/ST_NPoints.html>`__, Oracle, SpatiaLite

Accepts a single geographic field or expression and returns the number of points

```
in a geometry.
```

On MySQL, returns ``None`` for any non-``LINESTRING`` geometry.

```
``Perimeter``
```
```
=============
```

.. class:: Perimeter(expression, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_Perimeter.html>`__,

```
Oracle, SpatiaLite
```

Accepts a single geographic field or expression and returns the perimeter of the

geometry field as a :class:`~django.contrib.gis.measure.Distance` object.

```
``PointOnSurface``
```
```
==================
```

.. class:: PointOnSurface(expression, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_PointOnSurface.html>`__,

```
MariaDB, Oracle, SpatiaLite
```

Accepts a single geographic field or expression and returns a ``Point`` geometry

guaranteed to lie on the surface of the field; otherwise returns ``None``.

```
``Reverse``
```
```
===========
```

.. class:: Reverse(expression, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_Reverse.html>`__, Oracle,

```
SpatiaLite
```

Accepts a single geographic field or expression and returns a geometry with

```
reversed coordinates.
```
```
``Scale``
```
```
=========
```

.. class:: Scale(expression, x, y, z=0.0, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_Scale.html>`__, SpatiaLite

Accepts a single geographic field or expression and returns a geometry with

scaled coordinates by multiplying them with the ``x``, ``y``, and optionally

```
``z`` parameters.
```
```
``SnapToGrid``
```
```
==============
```

.. class:: SnapToGrid(expression, *args, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_SnapToGrid.html>`__,

```
SpatiaLite
```

Accepts a single geographic field or expression and returns a geometry with all

points snapped to the given grid.  How the geometry is snapped to the grid

depends on how many numeric (either float, integer, or long) arguments are

```
given.
```

===================  =====================================================

```
Number of Arguments  Description
```

===================  =====================================================

1                    A single size to snap both the X and Y grids to.

2                    X and Y sizes to snap the grid to.

4                    X, Y sizes and the corresponding X, Y origins.

===================  =====================================================

```
``SymDifference``
```
```
=================
```

.. class:: SymDifference(expr1, expr2, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-operator-functions.html#function_st-symdifference>`__,

`PostGIS <https://postgis.net/docs/ST_SymDifference.html>`__, Oracle,

```
SpatiaLite
```

Accepts two geographic fields or expressions and returns the geometric

symmetric difference (union without the intersection) between the given

```
parameters.
```
```
``Transform``
```
```
=============
```

.. class:: Transform(expression, srid, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_Transform.html>`__,

```
Oracle, SpatiaLite
```

Accepts a geographic field or expression and a SRID integer code, and returns

the transformed geometry to the spatial reference system specified by the

```
``srid`` parameter.
```
```
.. note::
```

    What spatial reference system an integer SRID corresponds to may depend on

    the spatial database used.  In other words, the SRID numbers used for Oracle

    are not necessarily the same as those used by PostGIS.

```
``Translate``
```
```
=============
```

.. class:: Translate(expression, x, y, z=0.0, **extra)

*Availability*: `PostGIS <https://postgis.net/docs/ST_Translate.html>`__,

```
SpatiaLite
```

Accepts a single geographic field or expression and returns a geometry with

its coordinates offset by the ``x``, ``y``, and optionally ``z`` numeric

```
parameters.
```
```
``Union``
```
```
=========
```

.. class:: Union(expr1, expr2, **extra)

```
*Availability*: MariaDB, `MySQL
```

<https://dev.mysql.com/doc/refman/en/spatial-operator-functions.html#function_st-union>`__,

`PostGIS <https://postgis.net/docs/ST_Union.html>`__, Oracle, SpatiaLite

Accepts two geographic fields or expressions and returns the union of both

```
geometries.
```