From 7bdb9a90d06a955d0ad099f9b72e6c2c30cb89dc Mon Sep 17 00:00:00 2001
From: Justin Bronn <jbronn@gmail.com>
Date: Tue, 30 Mar 2010 23:15:43 +0000
Subject: [PATCH] PostGIS 1.5 allows distance queries on non-point geographic
geometry columns with `ST_Distance_Sphere`, enabled this functionality.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@12890 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
.../gis/db/backends/postgis/operations.py | 12 ++++----
django/contrib/gis/tests/distapp/tests.py | 30 ++++++++++++-------
docs/ref/contrib/gis/db-api.txt | 24 +++++++++------
docs/ref/contrib/gis/model-api.txt | 22 +++++++-------
4 files changed, 53 insertions(+), 35 deletions(-)
diff --git a/django/contrib/gis/db/backends/postgis/operations.py b/django/contrib/gis/db/backends/postgis/operations.py
index c4576a3574..eeb9105002 100644
--- a/django/contrib/gis/db/backends/postgis/operations.py
+++ b/django/contrib/gis/db/backends/postgis/operations.py
@@ -536,12 +536,14 @@ class PostGISOperations(DatabaseOperations, BaseSpatialOperations):
op = op(self.geom_func_prefix, value[1])
elif lookup_type in self.distance_functions and lookup_type != 'dwithin':
if not field.geography and field.geodetic(self.connection):
- # Geodetic distances are only availble from Points to PointFields.
- if field.geom_type != 'POINT':
- raise ValueError('PostGIS spherical operations are only valid on PointFields.')
+ # Geodetic distances are only availble from Points to
+ # PointFields on PostGIS 1.4 and below.
+ if not self.connection.ops.geography:
+ if field.geom_type != 'POINT':
+ raise ValueError('PostGIS spherical operations are only valid on PointFields.')
- if str(geom.geom_type) != 'Point':
- raise ValueError('PostGIS geometry distance parameter is required to be of type Point.')
+ if str(geom.geom_type) != 'Point':
+ raise ValueError('PostGIS geometry distance parameter is required to be of type Point.')
# Setting up the geodetic operation appropriately.
if nparams == 3 and value[2] == 'spheroid':
diff --git a/django/contrib/gis/tests/distapp/tests.py b/django/contrib/gis/tests/distapp/tests.py
index 28e50a3571..aacb610dcc 100644
--- a/django/contrib/gis/tests/distapp/tests.py
+++ b/django/contrib/gis/tests/distapp/tests.py
@@ -265,21 +265,31 @@ class DistanceTest(unittest.TestCase):
def test05_geodetic_distance_lookups(self):
"Testing distance lookups on geodetic coordinate systems."
- if not oracle:
- # Oracle doesn't have this limitation -- PostGIS only allows geodetic
- # distance queries from Points to PointFields on geometry columns (geography
- # columns don't have that limitation).
- mp = GEOSGeometry('MULTIPOINT(0 0, 5 23)')
- self.assertRaises(ValueError, len,
- AustraliaCity.objects.filter(point__distance_lte=(mp, D(km=100))))
+ # Line is from Canberra to Sydney. Query is for all other cities within
+ # a 100km of that line (which should exclude only Hobart & Adelaide).
+ line = GEOSGeometry('LINESTRING(144.9630 -37.8143,151.2607 -33.8870)', 4326)
+ dist_qs = AustraliaCity.objects.filter(point__distance_lte=(line, D(km=100)))
+
+ if oracle or connection.ops.geography:
+ # Oracle and PostGIS 1.5 can do distance lookups on arbitrary geometries.
+ self.assertEqual(9, dist_qs.count())
+ self.assertEqual(['Batemans Bay', 'Canberra', 'Hillsdale',
+ 'Melbourne', 'Mittagong', 'Shellharbour',
+ 'Sydney', 'Thirroul', 'Wollongong'],
+ self.get_names(dist_qs))
+ else:
+ # PostGIS 1.4 and below only allows geodetic distance queries (utilizing
+ # ST_Distance_Sphere/ST_Distance_Spheroid) from Points to PointFields
+ # on geometry columns.
+ self.assertRaises(ValueError, dist_qs.count)
# Ensured that a ValueError was raised, none of the rest of the test is
# support on this backend, so bail now.
if spatialite: return
- # Too many params (4 in this case) should raise a ValueError.
- self.assertRaises(ValueError, len,
- AustraliaCity.objects.filter(point__distance_lte=('POINT(5 23)', D(km=100), 'spheroid', '4')))
+ # Too many params (4 in this case) should raise a ValueError.
+ self.assertRaises(ValueError, len,
+ AustraliaCity.objects.filter(point__distance_lte=('POINT(5 23)', D(km=100), 'spheroid', '4')))
# Not enough params should raise a ValueError.
self.assertRaises(ValueError, len,
diff --git a/docs/ref/contrib/gis/db-api.txt b/docs/ref/contrib/gis/db-api.txt
index 017c9ec142..0959156c43 100644
--- a/docs/ref/contrib/gis/db-api.txt
+++ b/docs/ref/contrib/gis/db-api.txt
@@ -160,21 +160,26 @@ to be in the units of the field.
.. note::
- For PostGIS users, the routine ``ST_distance_sphere``
+ For users of PostGIS 1.4 and below, the routine ``ST_Distance_Sphere``
is used by default for calculating distances on geographic coordinate systems
- -- which may only be called with point geometries [#fndistsphere]_. Thus,
- geographic distance lookups on traditional PostGIS geometry columns are
+ (e.g., WGS84) -- which may only be called with point geometries [#fndistsphere14]_.
+ Thus, geographic distance lookups on traditional PostGIS geometry columns are
only allowed on :class:`PointField` model fields using a point for the
geometry parameter.
.. note::
- PostGIS 1.5 introduced :ref:`geography columns <geography-type>`, which
- is limited on what geometry types distance queries are performed with. In
- other words, if you have ``geography=True`` in your geometry field
- definition you'll be allowed to peform arbitrary distance queries with your
- data in geodetic units of WGS84.
+ In PostGIS 1.5, ``ST_Distance_Sphere`` does *not* limit the geometry types
+ geographic distance queries are performed with. [#fndistsphere15]_ However,
+ these queries may take a long time, as great-circle distances must be
+ calculated on the fly for *every* row in the query. This is because the
+ spatial index on traditional geometry fields cannot be used.
+ For much better performance on WGS84 distance queries, consider using
+ :ref:`geography columns <geography-type>` in your database instead because
+ they are able to use their spatial index in distance queries.
+ You can tell GeoDjango to use a geography column by setting ``geography=True``
+ in your field definition.
For example, let's say we have a ``SouthTexasCity`` model (from the
`GeoDjango distance tests`__ ) on a *projected* coordinate system valid for cities
@@ -300,5 +305,6 @@ Method PostGIS Oracle SpatiaLite
.. [#fnwkt] *See* Open Geospatial Consortium, Inc., `OpenGIS Simple Feature Specification For SQL <http://www.opengis.org/docs/99-049.pdf>`_, Document 99-049 (May 5, 1999), at Ch. 3.2.5, p. 3-11 (SQL Textual Representation of Geometry).
.. [#fnewkb] *See* `PostGIS EWKB, EWKT and Canonical Forms <http://postgis.refractions.net/documentation/manual-1.5/ch04.html#EWKB_EWKT>`_, PostGIS documentation at Ch. 4.1.2.
.. [#fngeojson] *See* Howard Butler, Martin Daly, Allan Doyle, Tim Schaub, & Christopher Schmidt, `The GeoJSON Format Specification <http://geojson.org/geojson-spec.html>`_, Revision 1.0 (June 16, 2008).
-.. [#fndistsphere] *See* PostGIS 1.5 ``ST_distance_sphere`` `documentation <http://postgis.refractions.net/documentation/manual-1.5/ST_Distance_Sphere.html>`_.
+.. [#fndistsphere14] *See* `PostGIS 1.4 documentation <http://postgis.refractions.net/documentation/manual-1.4/ST_Distance_Sphere.html>`_ on ``ST_distance_sphere``.
+.. [#fndistsphere15] *See* `PostGIS 1.5 documentation <http://postgis.refractions.net/documentation/manual-1.5/ST_Distance_Sphere.html>`_ on ``ST_distance_sphere``.
.. [#] MySQL only supports bounding box operations (known as minimum bounding rectangles, or MBR, in MySQL). Thus, spatial lookups such as :lookup:`contains <gis-contains>` are really equivalent to :lookup:`bbcontains`.
diff --git a/docs/ref/contrib/gis/model-api.txt b/docs/ref/contrib/gis/model-api.txt
index 6b7b20d478..7c83a7e267 100644
--- a/docs/ref/contrib/gis/model-api.txt
+++ b/docs/ref/contrib/gis/model-api.txt
@@ -107,10 +107,11 @@ a flat surface is a straight line, the shortest path between two points on a cur
surface (such as the earth) is an *arc* of a `great circle`__. [#fnthematic]_ Thus,
additional computation is required to obtain distances in planar units (e.g.,
kilometers and miles). Using a geographic coordinate system may introduce
-complications for the developer later on. For example, PostGIS does not
-have the capability to perform distance calculations between non-point
-geometries using geographic coordinate systems, e.g., constructing a query to
-find all points within 5 miles of a county boundary stored as WGS84. [#fndist]_
+complications for the developer later on. For example, PostGIS versions 1.4
+and below do not have the capability to perform distance calculations between
+non-point geometries using geographic coordinate systems, e.g., constructing a
+query to find all points within 5 miles of a county boundary stored as WGS84.
+[#fndist]_
Portions of the earth's surface may projected onto a two-dimensional, or
Cartesian, plane. Projected coordinate systems are especially convenient
@@ -123,9 +124,10 @@ calculations.
.. note::
If you wish to peform arbitrary distance queries using non-point
- geometries, consider using PostGIS 1.5 and enabling the
- :attr:`GeometryField.geography` keyword to use the
- :ref:`geography database type <geography-type>` instead.
+ geometries in WGS84, consider upgrading to PostGIS 1.5. For
+ better performance, enable the :attr:`GeometryField.geography`
+ keyword so that :ref:`geography database type <geography-type>`
+ is used instead.
Additional Resources:
@@ -182,7 +184,7 @@ three-dimensonal support.
.. attribute:: GeometryField.geography
-If set to ``True``, this option will use create a database column of
+If set to ``True``, this option will create a database column of
type geography, rather than geometry. Please refer to the
:ref:`geography type <geography-type>` section below for more
details.
@@ -223,8 +225,6 @@ For more information, the PostGIS documentation contains a helpful section on
determining `when to use geography data type over geometry data type
<http://postgis.refractions.net/documentation/manual-1.5/ch04.html#PostGIS_GeographyVSGeometry>`_.
-
-
``GeoManager``
==============
@@ -262,5 +262,5 @@ for example::
.. [#fnsrid] Typically, SRID integer corresponds to an EPSG (`European Petroleum Survey Group <http://www.epsg.org>`_) identifier. However, it may also be associated with custom projections defined in spatial database's spatial reference systems table.
.. [#fnharvard] Harvard Graduate School of Design, `An Overview of Geodesy and Geographic Referencing Systems <http://www.gsd.harvard.edu/gis/manual/projections/fundamentals/>`_. This is an excellent resource for an overview of principles relating to geographic and Cartesian coordinate systems.
.. [#fnthematic] Terry A. Slocum, Robert B. McMaster, Fritz C. Kessler, & Hugh H. Howard, *Thematic Cartography and Geographic Visualization* (Prentice Hall, 2nd edition), at Ch. 7.1.3.
-.. [#fndist] This isn't impossible using GeoDjango; you could for example, take a known point in a projected coordinate system, buffer it to the appropriate radius, and then perform an intersection operation with the buffer transformed to the geographic coordinate system.
+.. [#fndist] This limitation does not apply to PostGIS 1.5. It should be noted that even in previous versions of PostGIS, this isn't impossible using GeoDjango; you could for example, take a known point in a projected coordinate system, buffer it to the appropriate radius, and then perform an intersection operation with the buffer transformed to the geographic coordinate system.
.. [#fngeography] Please refer to the `PostGIS Geography Type <http://postgis.refractions.net/documentation/manual-1.5/ch04.html#PostGIS_Geography>`_ documentation for more details.