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.

举例：

>>> 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:

Area

class Area(expression, \*extra*)

Availability: MariaDB, MySQL, Oracle, PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns the area of the field as an Area measure.

MySQL and SpatiaLite without LWGEOM don’t support area calculations on geographic SRSes.

AsGeoJSON

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

Availability: MariaDB (≥ 10.2.4), MySQL (≥ 5.7.5), Oracle, PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns a GeoJSON 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 GeoJSON Serializer.

举例：

>>> City.objects.annotate(json=AsGeoJSON('point')).get(name='Chicago').json
{"type":"Point","coordinates":[-87.65018,41.85039]}

Changed in Django 3.1:

Oracle support was added.

AsGML

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

Availability: Oracle, PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns a Geographic Markup Language (GML) representation of the geometry.

举例：

>>> 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>

AsKML

class AsKML(expression, precision=8, \*extra*)

Availability: PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns a Keyhole Markup Language (KML) representation of the geometry.

举例：

>>> 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>

Changed in Django 3.1:

The undocumented version parameter was removed.

AsSVG

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

Availability: PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns a Scalable Vector Graphics (SVG) representation of the geometry.

AsWKB

class AsWKB(expression, \*extra*)

New in Django 3.1.

Availability: MariaDB, MySQL, Oracle, PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns a Well-known binary (WKB) representation of the geometry.

举例：

>>> 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@'

AsWKT

class AsWKT(expression, \*extra*)

New in Django 3.1.

Availability: MariaDB, MySQL, Oracle, PostGIS, SpatiaLite

Accepts a single geographic field or expression and returns a Well-known text (WKT) representation of the geometry.

举例：

>>> City.objects.annotate(wkt=AsWKT('point')).get(name='Chelyabinsk').wkt
'POINT (55.137555 61.451728)'

Azimuth

class Azimuth(point_a, point_b, \*extra*)

Availability: PostGIS, SpatiaLite (LWGEOM)

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, Oracle

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, PostGIS, 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, PostGIS, 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, PostGIS, Oracle, SpatiaLite

Accepts two geographic fields or expressions and returns the distance between them, as a 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 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 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
...

注解

Because the distance attribute is a 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 Measurement Objects for usage details and the list of Supported units.

Envelope

class Envelope(expression, \*extra*)

Availability: MariaDB, MySQL, Oracle, PostGIS, 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, 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 (≥ 5.7.5), PostGIS, SpatiaLite (LWGEOM)

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.

GeometryDistance

class GeometryDistance(expr1, expr2, \*extra*)

Availability: PostGIS

Accepts two geographic fields or expressions and returns the distance between them. When used in an order_by() clause, it provides index-assisted nearest-neighbor result sets.

Intersection

class Intersection(expr1, expr2, \*extra*)

Availability: MariaDB, MySQL, PostGIS, Oracle, SpatiaLite

Accepts two geographic fields or expressions and returns the geometric intersection between them.

IsValid

class IsValid(expr)

Availability: MySQL (≥ 5.7.5), PostGIS, Oracle, SpatiaLite (LWGEOM)

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, Oracle, PostGIS, SpatiaLite

Accepts a single geographic linestring or multilinestring field or expression and returns its length as a 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, 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, SpatiaLite (LWGEOM)

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

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, PostGIS, 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, PostGIS, 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, Oracle, SpatiaLite

Accepts a single geographic field or expression and returns the perimeter of the geometry field as a Distance object.

PointOnSurface

class PointOnSurface(expression, \*extra*)

Availability: PostGIS, 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, 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, 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, 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.

SymDifference

class SymDifference(expr1, expr2, \*extra*)

Availability: MariaDB, MySQL, PostGIS, 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, 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.

注解

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, 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, PostGIS, Oracle, SpatiaLite

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