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c12a00e554
Added the IsValid and MakeValid database functions, and the isvalid lookup, all for PostGIS. Thanks Tim Graham for the review.
482 lines
16 KiB
Plaintext
482 lines
16 KiB
Plaintext
=============================
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Geographic Database Functions
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=============================
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.. module:: django.contrib.gis.db.models.functions
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:synopsis: Geographic Database Functions
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.. versionadded:: 1.9
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The functions documented on this page allow users to access geographic database
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functions to be used in annotations, aggregations, or filters in Django.
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Example::
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>>> from django.contrib.gis.db.models.functions import Length
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>>> Track.objects.annotate(length=Length('line')).filter(length__gt=100)
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Not all backends support all functions, so refer to the documentation of each
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function to see if your database backend supports the function you want to use.
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If you call a geographic function on a backend that doesn't support it, you'll
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get a ``NotImplementedError`` exception.
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Function's summary:
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================== ======================= ====================== =================== ================== =====================
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Measurement Relationships Operations Editors Output format Miscellaneous
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================== ======================= ====================== =================== ================== =====================
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:class:`Area` :class:`BoundingCircle` :class:`Difference` :class:`ForceRHR` :class:`AsGeoJSON` :class:`IsValid`
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:class:`Distance` :class:`Centroid` :class:`Intersection` :class:`MakeValid` :class:`AsGML` :class:`MemSize`
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:class:`Length` :class:`Envelope` :class:`SymDifference` :class:`Reverse` :class:`AsKML` :class:`NumGeometries`
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:class:`Perimeter` :class:`PointOnSurface` :class:`Union` :class:`Scale` :class:`AsSVG` :class:`NumPoints`
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:class:`SnapToGrid` :class:`GeoHash`
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:class:`Transform`
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:class:`Translate`
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================== ======================= ====================== =================== ================== =====================
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``Area``
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========
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.. class:: Area(expression, **extra)
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*Availability*: MySQL, Oracle, PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns the area of the
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field as an :class:`~django.contrib.gis.measure.Area` measure. On MySQL, a raw
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float value is returned, as it's not possible to automatically determine the
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unit of the field.
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``AsGeoJSON``
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=============
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.. class:: AsGeoJSON(expression, bbox=False, crs=False, precision=8, **extra)
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*Availability*: PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns a `GeoJSON
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<http://geojson.org/>`_ representation of the geometry. Note that the result is
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not a complete GeoJSON structure but only the ``geometry`` key content of a
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GeoJSON structure. See also :doc:`/ref/contrib/gis/serializers`.
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Example::
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>>> City.objects.annotate(json=AsGeoJSON('point')).get(name='Chicago').json
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{"type":"Point","coordinates":[-87.65018,41.85039]}
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===================== =====================================================
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Keyword Argument Description
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===================== =====================================================
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``bbox`` Set this to ``True`` if you want the bounding box
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to be included in the returned GeoJSON.
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``crs`` Set this to ``True`` if you want the coordinate
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reference system to be included in the returned
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GeoJSON.
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``precision`` It may be used to specify the number of significant
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digits for the coordinates in the GeoJSON
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representation -- the default value is 8.
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===================== =====================================================
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``AsGML``
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=========
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.. class:: AsGML(expression, version=2, precision=8, **extra)
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*Availability*: Oracle, PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns a `Geographic Markup
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Language (GML)`__ representation of the geometry.
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Example::
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>>> qs = Zipcode.objects.annotate(gml=AsGML('poly'))
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>>> print(qs[0].gml)
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<gml:Polygon srsName="EPSG:4326"><gml:OuterBoundaryIs>-147.78711,70.245363 ...
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-147.78711,70.245363</gml:OuterBoundaryIs></gml:Polygon>
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===================== =====================================================
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Keyword Argument Description
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===================== =====================================================
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``precision`` Not used on Oracle. It may be used to specify the number
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of significant digits for the coordinates in the GML
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representation -- the default value is 8.
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``version`` Not used on Oracle. It may be used to specify the GML
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version used, and may only be values of 2 or 3. The
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default value is 2.
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===================== =====================================================
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__ https://en.wikipedia.org/wiki/Geography_Markup_Language
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``AsKML``
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=========
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.. class:: AsKML(expression, precision=8, **extra)
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*Availability*: PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns a `Keyhole Markup
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Language (KML)`__ representation of the geometry.
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Example::
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>>> qs = Zipcode.objects.annotate(kml=AsKML('poly'))
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>>> print(qs[0].kml)
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<Polygon><outerBoundaryIs><LinearRing><coordinates>-103.04135,36.217596,0 ...
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-103.04135,36.217596,0</coordinates></LinearRing></outerBoundaryIs></Polygon>
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===================== =====================================================
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Keyword Argument Description
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===================== =====================================================
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``precision`` This keyword may be used to specify the number of
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significant digits for the coordinates in the KML
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representation -- the default value is 8.
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===================== =====================================================
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__ https://developers.google.com/kml/documentation/
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``AsSVG``
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=========
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.. class:: AsSVG(expression, relative=False, precision=8, **extra)
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*Availability*: PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns a `Scalable Vector
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Graphics (SVG)`__ representation of the geometry.
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===================== =====================================================
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Keyword Argument Description
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===================== =====================================================
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``relative`` If set to ``True``, the path data will be implemented
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in terms of relative moves. Defaults to ``False``,
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meaning that absolute moves are used instead.
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``precision`` This keyword may be used to specify the number of
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significant digits for the coordinates in the SVG
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representation -- the default value is 8.
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===================== =====================================================
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__ http://www.w3.org/Graphics/SVG/
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``BoundingCircle``
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==================
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.. class:: BoundingCircle(expression, num_seg=48, **extra)
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*Availability*: `PostGIS <http://postgis.net/docs/ST_MinimumBoundingCircle.html>`__
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Accepts a single geographic field or expression and returns the smallest circle
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polygon that can fully contain the geometry.
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``Centroid``
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============
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.. class:: Centroid(expression, **extra)
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*Availability*: MySQL, PostGIS, Oracle, SpatiaLite
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Accepts a single geographic field or expression and returns the ``centroid``
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value of the geometry.
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``Difference``
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==============
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.. class:: Difference(expr1, expr2, **extra)
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*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
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Accepts two geographic fields or expressions and returns the geometric
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difference, that is the part of geometry A that does not intersect with
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geometry B.
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.. versionchanged:: 1.10
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MySQL support was added.
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``Distance``
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============
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.. class:: Distance(expr1, expr2, spheroid=None, **extra)
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*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
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Accepts two geographic fields or expressions and returns the distance between
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them, as a :class:`~django.contrib.gis.measure.Distance` object. On MySQL, a raw
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float value is returned, as it's not possible to automatically determine the
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unit of the field.
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On backends that support distance calculation on geodetic coordinates, the
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proper backend function is automatically chosen depending on the SRID value of
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the geometries (e.g. ``ST_Distance_Sphere`` on PostGIS).
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When distances are calculated with geodetic (angular) coordinates, as is the
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case with the default WGS84 (4326) SRID, you can set the ``spheroid`` keyword
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argument to decide if the calculation should be based on a simple sphere (less
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accurate, less resource-intensive) or on a spheroid (more accurate, more
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resource-intensive).
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In the following example, the distance from the city of Hobart to every other
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:class:`~django.contrib.gis.db.models.PointField` in the ``AustraliaCity``
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queryset is calculated::
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>>> from django.contrib.gis.db.models.functions import Distance
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>>> pnt = AustraliaCity.objects.get(name='Hobart').point
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>>> for city in AustraliaCity.objects.annotate(distance=Distance('point', pnt)):
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... print(city.name, city.distance)
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Wollongong 990071.220408 m
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Shellharbour 972804.613941 m
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Thirroul 1002334.36351 m
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...
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.. note::
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Because the ``distance`` attribute is a
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:class:`~django.contrib.gis.measure.Distance` object, you can easily express
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the value in the units of your choice. For example, ``city.distance.mi`` is
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the distance value in miles and ``city.distance.km`` is the distance value
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in kilometers. See :doc:`measure` for usage details and the list of
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:ref:`supported_units`.
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``Envelope``
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============
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.. class:: Envelope(expression, **extra)
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*Availability*: MySQL, PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns the geometry
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representing the bounding box of the geometry.
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``ForceRHR``
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============
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.. class:: ForceRHR(expression, **extra)
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*Availability*: `PostGIS <http://postgis.net/docs/ST_ForceRHR.html>`__
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Accepts a single geographic field or expression and returns a modified version
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of the polygon/multipolygon in which all of the vertices follow the
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right-hand rule.
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``GeoHash``
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===========
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.. class:: GeoHash(expression, **extra)
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*Availability*: PostGIS, SpatiaLite (≥ 4.0, LWGEOM)
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Accepts a single geographic field or expression and returns a `GeoHash`__
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representation of the geometry.
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.. versionchanged:: 1.10
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SpatiaLite support was added.
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__ https://en.wikipedia.org/wiki/Geohash
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``Intersection``
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================
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.. class:: Intersection(expr1, expr2, **extra)
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*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
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Accepts two geographic fields or expressions and returns the geometric
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intersection between them.
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.. versionchanged:: 1.10
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MySQL support was added.
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``IsValid``
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===========
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.. class:: IsValid(expr)
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.. versionadded:: 1.10
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*Availability*: PostGIS
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Accepts a geographic field or expression and tests if the value is well formed.
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Returns ``True`` if its value is a valid geometry and ``False`` otherwise.
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``Length``
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==========
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.. class:: Length(expression, spheroid=True, **extra)
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*Availability*: MySQL, Oracle, PostGIS, SpatiaLite
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Accepts a single geographic linestring or multilinestring field or expression
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and returns its length as an :class:`~django.contrib.gis.measure.Distance`
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measure. On MySQL, a raw float value is returned, as it's not possible to
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automatically determine the unit of the field.
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On PostGIS and SpatiaLite, when the coordinates are geodetic (angular), you can
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specify if the calculation should be based on a simple sphere (less
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accurate, less resource-intensive) or on a spheroid (more accurate, more
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resource-intensive) with the ``spheroid`` keyword argument.
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``MakeValid``
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=============
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.. class:: MakeValid(expr)
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.. versionadded:: 1.10
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*Availability*: PostGIS
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Accepts a geographic field or expression and attempts to convert the value into
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a valid geometry without losing any of the input vertices. Geometries that are
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already valid are returned without changes. Simple polygons might become a
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multipolygon and the result might be of lower dimension than the input.
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``MemSize``
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===========
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.. class:: MemSize(expression, **extra)
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*Availability*: PostGIS
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Accepts a single geographic field or expression and returns the memory size
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(number of bytes) that the geometry field takes.
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``NumGeometries``
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=================
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.. class:: NumGeometries(expression, **extra)
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*Availability*: MySQL, PostGIS, Oracle, SpatiaLite
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Accepts a single geographic field or expression and returns the number of
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geometries if the geometry field is a collection (e.g., a ``GEOMETRYCOLLECTION``
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or ``MULTI*`` field); otherwise returns ``None``.
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``NumPoints``
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=============
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.. class:: NumPoints(expression, **extra)
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*Availability*: MySQL, PostGIS, Oracle, SpatiaLite
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Accepts a single geographic field or expression and returns the number of points
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in the first linestring in the geometry field; otherwise returns ``None``.
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``Perimeter``
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=============
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.. class:: Perimeter(expression, **extra)
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*Availability*: PostGIS, Oracle, SpatiaLite (≥ 4.0)
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Accepts a single geographic field or expression and returns the perimeter of the
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geometry field as a :class:`~django.contrib.gis.measure.Distance` object. On
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MySQL, a raw float value is returned, as it's not possible to automatically
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determine the unit of the field.
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``PointOnSurface``
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==================
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.. class:: PointOnSurface(expression, **extra)
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*Availability*: PostGIS, Oracle, SpatiaLite
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Accepts a single geographic field or expression and returns a ``Point`` geometry
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guaranteed to lie on the surface of the field; otherwise returns ``None``.
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``Reverse``
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===========
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.. class:: Reverse(expression, **extra)
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*Availability*: PostGIS, Oracle, SpatiaLite (≥ 4.0)
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Accepts a single geographic field or expression and returns a geometry with
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reversed coordinates.
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``Scale``
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=========
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.. class:: Scale(expression, x, y, z=0.0, **extra)
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*Availability*: PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns a geometry with
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scaled coordinates by multiplying them with the ``x``, ``y``, and optionally
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``z`` parameters.
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``SnapToGrid``
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==============
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.. class:: SnapToGrid(expression, *args, **extra)
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*Availability*: PostGIS, SpatiaLite (≥ 3.1)
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Accepts a single geographic field or expression and returns a geometry with all
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points snapped to the given grid. How the geometry is snapped to the grid
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depends on how many numeric (either float, integer, or long) arguments are
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given.
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=================== =====================================================
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Number of Arguments Description
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=================== =====================================================
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1 A single size to snap both the X and Y grids to.
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2 X and Y sizes to snap the grid to.
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4 X, Y sizes and the corresponding X, Y origins.
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=================== =====================================================
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``SymDifference``
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=================
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.. class:: SymDifference(expr1, expr2, **extra)
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*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
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Accepts two geographic fields or expressions and returns the geometric
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symmetric difference (union without the intersection) between the given
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parameters.
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.. versionchanged:: 1.10
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MySQL support was added.
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``Transform``
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=============
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.. class:: Transform(expression, srid, **extra)
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*Availability*: PostGIS, Oracle, SpatiaLite
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Accepts a geographic field or expression and a SRID integer code, and returns
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the transformed geometry to the spatial reference system specified by the
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``srid`` parameter.
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.. note::
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What spatial reference system an integer SRID corresponds to may depend on
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the spatial database used. In other words, the SRID numbers used for Oracle
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are not necessarily the same as those used by PostGIS.
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``Translate``
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=============
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.. class:: Translate(expression, x, y, z=0.0, **extra)
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*Availability*: PostGIS, SpatiaLite
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Accepts a single geographic field or expression and returns a geometry with
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its coordinates offset by the ``x``, ``y``, and optionally ``z`` numeric
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parameters.
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``Union``
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=========
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.. class:: Union(expr1, expr2, **extra)
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*Availability*: MySQL (≥ 5.6.1), PostGIS, Oracle, SpatiaLite
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Accepts two geographic fields or expressions and returns the union of both
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geometries.
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