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 |
---|---|---|---|---|---|
Area | BoundingCircle | Difference | ForceRHR | AsGeoJSON | IsValid |
Distance | Centroid | Intersection | MakeValid | AsGML | MemSize |
Length | Envelope | SymDifference | Reverse | AsKML | NumGeometries |
Perimeter | PointOnSurface | Union | Scale | AsSVG | NumPoints |
SnapToGrid | GeoHash | ||||
Transform | |||||
Translate |
Area
class Area(expression, **extra)
Availability: 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.
In older versions, a raw value was returned on MySQL when used on projected SRS.
AsGeoJSON
class AsGeoJSON(expression, bbox=False, crs=False, precision=8, **extra)
Availability: 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.
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. |
crs | Set this to True if you want the coordinate reference system to be included in the returned GeoJSON. |
precision | It may be used to specify the number of significant digits for the coordinates in the GeoJSON representation – the default value is 8. |
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.
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. |
Oracle support was added.
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.
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. |
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.
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. |
BoundingCircle
class BoundingCircle(expression, num_seg=48, **extra)
Availability: PostGIS, Oracle (≥ 12.1.0.2)
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.
Oracle support was added.
Centroid
class Centroid(expression, **extra)
Availability: 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: MySQL (≥ 5.6.1), 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.
MySQL support was added.
Distance
class Distance(expr1, expr2, spheroid=None, **extra)
Availability: MySQL (≥ 5.6.1), 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 ...
Note
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.
In older versions, a raw value was returned on MySQL when used on projected SRS.
Envelope
class Envelope(expression, **extra)
Availability: MySQL, PostGIS, SpatiaLite
Accepts a single geographic field or expression and returns the geometry representing the bounding box of the geometry.
ForceRHR
class ForceRHR(expression, **extra)
Availability: PostGIS
Accepts a single geographic field or expression and returns a modified version of the polygon/multipolygon in which all of the vertices follow the right-hand rule.
GeoHash
class GeoHash(expression, precision=None, **extra)
Availability: 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.
SpatiaLite support was added.
Intersection
class Intersection(expr1, expr2, **extra)
Availability: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
Accepts two geographic fields or expressions and returns the geometric intersection between them.
MySQL support was added.
IsValid
class IsValid(expr)
Availability: 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.
SpatiaLite and Oracle support was added.
Length
class Length(expression, spheroid=True, **extra)
Availability: 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.
In older versions, a raw value was returned on MySQL.
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.
SpatiaLite support was added.
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: 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: MySQL, PostGIS, Oracle, SpatiaLite
Accepts a single geographic field or expression and returns the number of points in the first linestring in the geometry field; otherwise returns None
.
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, 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.
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: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
Accepts two geographic fields or expressions and returns the geometric symmetric difference (union without the intersection) between the given parameters.
MySQL support was added.
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.
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, 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: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
Accepts two geographic fields or expressions and returns the union of both geometries.
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Licensed under the BSD License.
https://docs.djangoproject.com/en/1.11/ref/contrib/gis/functions/