mirrors/django
1
0
Fork 0
mirror of https://github.com/django/django.git synced 2025-10-31 09:41:08 +00:00
Code Issues 32 Releases Wiki Activity

PostGIS 1.5 allows distance queries on non-point geographic geometry columns with ST_Distance_Sphere, enabled this functionality.

Browse Source 
git-svn-id: http://code.djangoproject.com/svn/django/trunk@12890 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Justin Bronn
2010-03-30 23:15:43 +00:00
parent dafc077e4a
commit 7bdb9a90d0
4 changed files with 53 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
docs/ref/contrib/gis/db-api.txt
View File

@@ -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`.