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 |
|---|---|---|---|---|---|
Area |
Azimuth |
Difference |
ForcePolygonCW |
AsGeoJSON |
IsValid |
Distance |
BoundingCircle |
Intersection |
ForceRHR |
AsGML |
MemSize |
Length |
Centroid |
SymDifference |
MakeValid |
AsKML |
NumGeometries |
Perimeter |
Envelope |
Union |
Reverse |
AsSVG |
NumPoints |
LineLocatePoint |
Scale |
GeoHash |
|||
PointOnSurface |
SnapToGrid |
||||
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.
AsGeoJSON¶
-
class
AsGeoJSON(expression, bbox=False, crs=False, precision=8, **extra)¶
Availability: MySQL (≥ 5.7.5), 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. Ignored on MySQL. |
precision |
It may be used to specify the number of significant digits for the coordinates in the GeoJSON representation – the default value is 8. |
MySQL 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.
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. |
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. |
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)¶
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: 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, 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: 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
...
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.
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.
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.
ForceRHR¶
-
class
ForceRHR(expression, **extra)¶
Deprecated since version 2.1: Use ForcePolygonCW instead.
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: 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.
MySQL support was added.
Intersection¶
-
class
Intersection(expr1, expr2, **extra)¶
Availability: 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.
MySQL 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.
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: 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 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, 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, 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.
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.
