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790 lines
27 KiB
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790 lines
27 KiB
Plaintext
==================
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GeoDjango Tutorial
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==================
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Introduction
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============
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GeoDjango is an add-on for Django that turns it into a world-class geographic
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Web framework. GeoDjango strives to make it as simple as possible to create
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geographic Web applications, like location-based services. Some features
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include:
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* Django model fields for `OGC`_ geometries.
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* Extensions to Django's ORM for the querying and manipulation of spatial data.
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* Loosely-coupled, high-level Python interfaces for GIS geometry operations and
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data formats.
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* Editing of geometry fields inside the admin.
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This tutorial assumes a familiarity with Django; thus, if you're brand new to
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Django please read through the :doc:`regular tutorial </intro/tutorial01>` to
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introduce yourself with basic Django concepts.
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.. note::
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GeoDjango has special prerequisites overwhat is required by Django --
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please consult the :ref:`installation documentation <ref-gis-install>`
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for more details.
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This tutorial will guide you through the creation of a geographic Web
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application for viewing the `world borders`_. [#]_ Some of the code
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used in this tutorial is taken from and/or inspired by the `GeoDjango
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basic apps`_ project. [#]_
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.. note::
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Proceed through the tutorial sections sequentially for step-by-step
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instructions.
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.. _OGC: http://www.opengeospatial.org/
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.. _world borders: http://thematicmapping.org/downloads/world_borders.php
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.. _GeoDjango basic apps: http://code.google.com/p/geodjango-basic-apps/
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Setting Up
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==========
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Create a Spatial Database
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-------------------------
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.. note::
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MySQL and Oracle users can skip this section because spatial types
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are already built into the database.
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First, a spatial database needs to be created for our project. If using
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PostgreSQL and PostGIS, then the following commands will
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create the database from a :ref:`spatial database template
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<spatialdb_template>`:
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.. code-block:: bash
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$ createdb -T template_postgis geodjango
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.. note::
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This command must be issued by a database user that has permissions to
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create a database. Here is an example set of commands to create such
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a user:
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.. code-block:: bash
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$ sudo su - postgres
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$ createuser --createdb geo
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$ exit
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Replace ``geo`` to correspond to the system login user name will be
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connecting to the database. For example, ``johndoe`` if that is the
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system user that will be running GeoDjango.
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Users of SQLite and SpatiaLite should consult the instructions on how
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to create a :ref:`SpatiaLite database <create_spatialite_db>`.
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Create GeoDjango Project
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------------------------
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Use the ``django-admin.py`` script like normal to create a ``geodjango``
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project:
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.. code-block:: bash
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$ django-admin.py startproject geodjango
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With the project initialized, now create a ``world`` Django application within
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the ``geodjango`` project:
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.. code-block:: bash
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$ cd geodjango
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$ python manage.py startapp world
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Configure ``settings.py``
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-------------------------
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The ``geodjango`` project settings are stored in the ``settings.py`` file. Edit
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the database connection settings appropriately::
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DATABASES = {
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'default': {
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'ENGINE': 'django.contrib.gis.db.backends.postgis',
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'NAME': 'geodjango',
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'USER': 'geo',
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}
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}
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.. note::
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These database settings are for Django 1.2 and above.
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In addition, modify the :setting:`INSTALLED_APPS` setting to include
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:mod:`django.contrib.admin`, :mod:`django.contrib.gis`,
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and ``world`` (our newly created application)::
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INSTALLED_APPS = (
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'django.contrib.auth',
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'django.contrib.contenttypes',
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'django.contrib.sessions',
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'django.contrib.sites',
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'django.contrib.admin',
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'django.contrib.gis',
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'world'
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)
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Geographic Data
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===============
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.. _worldborders:
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World Borders
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-------------
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The world borders data is available in this `zip file`__. Create a data
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directory in the ``world`` application, download the world borders data, and
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unzip. On GNU/Linux platforms the following commands should do it:
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.. code-block:: bash
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$ mkdir world/data
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$ cd world/data
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$ wget http://thematicmapping.org/downloads/TM_WORLD_BORDERS-0.3.zip
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$ unzip TM_WORLD_BORDERS-0.3.zip
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$ cd ../..
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The world borders ZIP file contains a set of data files collectively known as
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an `ESRI Shapefile`__, one of the most popular geospatial data formats. When
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unzipped the world borders data set includes files with the following
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extensions:
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* ``.shp``: Holds the vector data for the world borders geometries.
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* ``.shx``: Spatial index file for geometries stored in the ``.shp``.
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* ``.dbf``: Database file for holding non-geometric attribute data
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(e.g., integer and character fields).
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* ``.prj``: Contains the spatial reference information for the geographic
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data stored in the shapefile.
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__ http://thematicmapping.org/downloads/TM_WORLD_BORDERS-0.3.zip
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__ http://en.wikipedia.org/wiki/Shapefile
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Use ``ogrinfo`` to examine spatial data
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---------------------------------------
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The GDAL ``ogrinfo`` utility is excellent for examining metadata about
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shapefiles (or other vector data sources):
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.. code-block:: bash
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$ ogrinfo world/data/TM_WORLD_BORDERS-0.3.shp
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INFO: Open of `world/data/TM_WORLD_BORDERS-0.3.shp'
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using driver `ESRI Shapefile' successful.
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1: TM_WORLD_BORDERS-0.3 (Polygon)
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Here ``ogrinfo`` is telling us that the shapefile has one layer, and that
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layer contains polygon data. To find out more we'll specify the layer name
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and use the ``-so`` option to get only important summary information:
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.. code-block:: bash
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$ ogrinfo -so world/data/TM_WORLD_BORDERS-0.3.shp TM_WORLD_BORDERS-0.3
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INFO: Open of `world/data/TM_WORLD_BORDERS-0.3.shp'
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using driver `ESRI Shapefile' successful.
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Layer name: TM_WORLD_BORDERS-0.3
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Geometry: Polygon
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Feature Count: 246
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Extent: (-180.000000, -90.000000) - (180.000000, 83.623596)
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Layer SRS WKT:
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GEOGCS["GCS_WGS_1984",
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DATUM["WGS_1984",
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SPHEROID["WGS_1984",6378137.0,298.257223563]],
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PRIMEM["Greenwich",0.0],
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UNIT["Degree",0.0174532925199433]]
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FIPS: String (2.0)
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ISO2: String (2.0)
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ISO3: String (3.0)
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UN: Integer (3.0)
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NAME: String (50.0)
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AREA: Integer (7.0)
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POP2005: Integer (10.0)
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REGION: Integer (3.0)
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SUBREGION: Integer (3.0)
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LON: Real (8.3)
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LAT: Real (7.3)
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This detailed summary information tells us the number of features in the layer
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(246), the geographical extent, the spatial reference system ("SRS WKT"),
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as well as detailed information for each attribute field. For example,
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``FIPS: String (2.0)`` indicates that there's a ``FIPS`` character field
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with a maximum length of 2; similarly, ``LON: Real (8.3)`` is a floating-point
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field that holds a maximum of 8 digits up to three decimal places. Although
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this information may be found right on the `world borders`_ Web site, this
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shows you how to determine this information yourself when such metadata is not
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provided.
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Geographic Models
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=================
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Defining a Geographic Model
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---------------------------
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Now that we've examined our world borders data set using ``ogrinfo``, we can
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create a GeoDjango model to represent this data::
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from django.contrib.gis.db import models
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class WorldBorder(models.Model):
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# Regular Django fields corresponding to the attributes in the
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# world borders shapefile.
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name = models.CharField(max_length=50)
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area = models.IntegerField()
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pop2005 = models.IntegerField('Population 2005')
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fips = models.CharField('FIPS Code', max_length=2)
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iso2 = models.CharField('2 Digit ISO', max_length=2)
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iso3 = models.CharField('3 Digit ISO', max_length=3)
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un = models.IntegerField('United Nations Code')
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region = models.IntegerField('Region Code')
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subregion = models.IntegerField('Sub-Region Code')
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lon = models.FloatField()
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lat = models.FloatField()
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# GeoDjango-specific: a geometry field (MultiPolygonField), and
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# overriding the default manager with a GeoManager instance.
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mpoly = models.MultiPolygonField()
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objects = models.GeoManager()
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# Returns the string representation of the model.
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def __unicode__(self):
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return self.name
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Two important things to note:
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1. The ``models`` module is imported from :mod:`django.contrib.gis.db`.
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2. The model overrides its default manager with
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:class:`~django.contrib.gis.db.models.GeoManager`; this is *required*
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to perform spatial queries.
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When declaring a geometry field on your model the default spatial reference
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system is WGS84 (meaning the `SRID`__ is 4326) -- in other words, the field
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coordinates are in longitude/latitude pairs in units of degrees. If you want
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the coordinate system to be different, then SRID of the geometry field may be
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customized by setting the ``srid`` with an integer corresponding to the
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coordinate system of your choice.
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__ http://en.wikipedia.org/wiki/SRID
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Run ``syncdb``
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--------------
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After you've defined your model, it needs to be synced with the spatial
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database. First, let's look at the SQL that will generate the table for the
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``WorldBorder`` model::
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$ python manage.py sqlall world
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This management command should produce the following output:
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.. code-block:: sql
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BEGIN;
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CREATE TABLE "world_worldborders" (
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"id" serial NOT NULL PRIMARY KEY,
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"name" varchar(50) NOT NULL,
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"area" integer NOT NULL,
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"pop2005" integer NOT NULL,
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"fips" varchar(2) NOT NULL,
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"iso2" varchar(2) NOT NULL,
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"iso3" varchar(3) NOT NULL,
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"un" integer NOT NULL,
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"region" integer NOT NULL,
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"subregion" integer NOT NULL,
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"lon" double precision NOT NULL,
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"lat" double precision NOT NULL
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)
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;
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SELECT AddGeometryColumn('world_worldborders', 'mpoly', 4326, 'MULTIPOLYGON', 2);
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ALTER TABLE "world_worldborders" ALTER "mpoly" SET NOT NULL;
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CREATE INDEX "world_worldborders_mpoly_id" ON "world_worldborders" USING GIST ( "mpoly" GIST_GEOMETRY_OPS );
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COMMIT;
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If satisfied, you may then create this table in the database by running the
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``syncdb`` management command::
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$ python manage.py syncdb
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Creating table world_worldborders
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Installing custom SQL for world.WorldBorder model
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The ``syncdb`` command may also prompt you to create an admin user; go ahead
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and do so (not required now, may be done at any point in the future using the
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``createsuperuser`` management command).
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Importing Spatial Data
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======================
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This section will show you how to take the data from the world borders
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shapefile and import it into GeoDjango models using the
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:ref:`ref-layermapping`.
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There are many different ways to import data in to a spatial database --
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besides the tools included within GeoDjango, you may also use the following to
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populate your spatial database:
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* `ogr2ogr`_: Command-line utility, included with GDAL, that
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supports loading a multitude of vector data formats into
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the PostGIS, MySQL, and Oracle spatial databases.
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* `shp2pgsql`_: This utility is included with PostGIS and only supports
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ESRI shapefiles.
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.. _ogr2ogr: http://www.gdal.org/ogr2ogr.html
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.. _shp2pgsql: http://postgis.refractions.net/documentation/manual-1.5/ch04.html#shp2pgsql_usage
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.. _gdalinterface:
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GDAL Interface
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--------------
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Earlier we used the ``ogrinfo`` to explore the contents of the world borders
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shapefile. Included within GeoDjango is an interface to GDAL's powerful OGR
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library -- in other words, you'll be able explore all the vector data sources
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that OGR supports via a Pythonic API.
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First, invoke the Django shell:
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.. code-block:: bash
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$ python manage.py shell
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If the :ref:`worldborders` data was downloaded like earlier in the
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tutorial, then we can determine the path using Python's built-in
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``os`` module::
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>>> import os
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>>> from geodjango import world
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>>> world_shp = os.path.abspath(os.path.join(os.path.dirname(world.__file__),
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... 'data/TM_WORLD_BORDERS-0.3.shp'))
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Now, the world borders shapefile may be opened using GeoDjango's
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:class:`~django.contrib.gis.gdal.DataSource` interface::
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>>> from django.contrib.gis.gdal import *
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>>> ds = DataSource(world_shp)
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>>> print ds
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/ ... /geodjango/world/data/TM_WORLD_BORDERS-0.3.shp (ESRI Shapefile)
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Data source objects can have different layers of geospatial features; however,
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shapefiles are only allowed to have one layer::
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>>> print len(ds)
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1
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>>> lyr = ds[0]
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>>> print lyr
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TM_WORLD_BORDERS-0.3
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You can see what the geometry type of the layer is and how many features it
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contains::
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>>> print lyr.geom_type
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Polygon
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>>> print len(lyr)
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246
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.. note::
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Unfortunately the shapefile data format does not allow for greater
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specificity with regards to geometry types. This shapefile, like
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many others, actually includes ``MultiPolygon`` geometries in its
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features. You need to watch out for this when creating your models
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as a GeoDjango ``PolygonField`` will not accept a ``MultiPolygon``
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type geometry -- thus a ``MultiPolygonField`` is used in our model's
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definition instead.
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The :class:`~django.contrib.gis.gdal.Layer` may also have a spatial reference
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system associated with it -- if it does, the ``srs`` attribute will return a
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:class:`~django.contrib.gis.gdal.SpatialReference` object::
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>>> srs = lyr.srs
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>>> print srs
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GEOGCS["GCS_WGS_1984",
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DATUM["WGS_1984",
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SPHEROID["WGS_1984",6378137.0,298.257223563]],
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PRIMEM["Greenwich",0.0],
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UNIT["Degree",0.0174532925199433]]
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>>> srs.proj4 # PROJ.4 representation
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'+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs '
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Here we've noticed that the shapefile is in the popular WGS84 spatial reference
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system -- in other words, the data uses units of degrees longitude and
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latitude.
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In addition, shapefiles also support attribute fields that may contain
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additional data. Here are the fields on the World Borders layer:
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>>> print lyr.fields
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['FIPS', 'ISO2', 'ISO3', 'UN', 'NAME', 'AREA', 'POP2005', 'REGION', 'SUBREGION', 'LON', 'LAT']
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Here we are examining the OGR types (e.g., whether a field is an integer or
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a string) associated with each of the fields:
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>>> [fld.__name__ for fld in lyr.field_types]
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['OFTString', 'OFTString', 'OFTString', 'OFTInteger', 'OFTString', 'OFTInteger', 'OFTInteger', 'OFTInteger', 'OFTInteger', 'OFTReal', 'OFTReal']
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You can iterate over each feature in the layer and extract information from both
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the feature's geometry (accessed via the ``geom`` attribute) as well as the
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feature's attribute fields (whose **values** are accessed via ``get()``
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method)::
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>>> for feat in lyr:
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... print feat.get('NAME'), feat.geom.num_points
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...
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Guernsey 18
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Jersey 26
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South Georgia South Sandwich Islands 338
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Taiwan 363
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:class:`~django.contrib.gis.gdal.Layer` objects may be sliced::
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>>> lyr[0:2]
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[<django.contrib.gis.gdal.feature.Feature object at 0x2f47690>, <django.contrib.gis.gdal.feature.Feature object at 0x2f47650>]
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And individual features may be retrieved by their feature ID::
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>>> feat = lyr[234]
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>>> print feat.get('NAME')
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San Marino
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Here the boundary geometry for San Marino is extracted and looking
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exported to WKT and GeoJSON::
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>>> geom = feat.geom
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>>> print geom.wkt
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POLYGON ((12.415798 43.957954,12.450554 ...
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>>> print geom.json
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{ "type": "Polygon", "coordinates": [ [ [ 12.415798, 43.957954 ], [ 12.450554, 43.979721 ], ...
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``LayerMapping``
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----------------
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We're going to dive right in -- create a file called ``load.py`` inside the
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``world`` application, and insert the following::
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import os
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from django.contrib.gis.utils import LayerMapping
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from models import WorldBorder
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world_mapping = {
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'fips' : 'FIPS',
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'iso2' : 'ISO2',
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'iso3' : 'ISO3',
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'un' : 'UN',
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'name' : 'NAME',
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'area' : 'AREA',
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'pop2005' : 'POP2005',
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'region' : 'REGION',
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'subregion' : 'SUBREGION',
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'lon' : 'LON',
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'lat' : 'LAT',
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'mpoly' : 'MULTIPOLYGON',
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}
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world_shp = os.path.abspath(os.path.join(os.path.dirname(__file__), 'data/TM_WORLD_BORDERS-0.3.shp'))
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def run(verbose=True):
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lm = LayerMapping(WorldBorder, world_shp, world_mapping,
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transform=False, encoding='iso-8859-1')
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lm.save(strict=True, verbose=verbose)
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A few notes about what's going on:
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* Each key in the ``world_mapping`` dictionary corresponds to a field in the
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``WorldBorder`` model, and the value is the name of the shapefile field
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that data will be loaded from.
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* The key ``mpoly`` for the geometry field is ``MULTIPOLYGON``, the
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geometry type we wish to import as. Even if simple polygons are encountered
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in the shapefile they will automatically be converted into collections prior
|
|
to insertion into the database.
|
|
* The path to the shapefile is not absolute -- in other words, if you move the
|
|
``world`` application (with ``data`` subdirectory) to a different location,
|
|
then the script will still work.
|
|
* The ``transform`` keyword is set to ``False`` because the data in the
|
|
shapefile does not need to be converted -- it's already in WGS84 (SRID=4326).
|
|
* The ``encoding`` keyword is set to the character encoding of string values in
|
|
the shapefile. This ensures that string values are read and saved correctly
|
|
from their original encoding system.
|
|
|
|
Afterwards, invoke the Django shell from the ``geodjango`` project directory:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py shell
|
|
|
|
Next, import the ``load`` module, call the ``run`` routine, and watch ``LayerMapping``
|
|
do the work::
|
|
|
|
>>> from world import load
|
|
>>> load.run()
|
|
|
|
|
|
.. _ogrinspect-intro:
|
|
|
|
Try ``ogrinspect``
|
|
------------------
|
|
Now that you've seen how to define geographic models and import data with the
|
|
:ref:`ref-layermapping`, it's possible to further automate this process with
|
|
use of the :djadmin:`ogrinspect` management command. The :djadmin:`ogrinspect`
|
|
command introspects a GDAL-supported vector data source (e.g., a shapefile)
|
|
and generates a model definition and ``LayerMapping`` dictionary automatically.
|
|
|
|
The general usage of the command goes as follows:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py ogrinspect [options] <data_source> <model_name> [options]
|
|
|
|
Where ``data_source`` is the path to the GDAL-supported data source and
|
|
``model_name`` is the name to use for the model. Command-line options may
|
|
be used to further define how the model is generated.
|
|
|
|
For example, the following command nearly reproduces the ``WorldBorder`` model
|
|
and mapping dictionary created above, automatically:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py ogrinspect world/data/TM_WORLD_BORDERS-0.3.shp WorldBorder --srid=4326 --mapping --multi
|
|
|
|
A few notes about the command-line options given above:
|
|
|
|
* The ``--srid=4326`` option sets the SRID for the geographic field.
|
|
* The ``--mapping`` option tells ``ogrinspect`` to also generate a
|
|
mapping dictionary for use with
|
|
:class:`~django.contrib.gis.utils.LayerMapping`.
|
|
* The ``--multi`` option is specified so that the geographic field is a
|
|
:class:`~django.contrib.gis.db.models.MultiPolygonField` instead of just a
|
|
:class:`~django.contrib.gis.db.models.PolygonField`.
|
|
|
|
The command produces the following output, which may be copied
|
|
directly into the ``models.py`` of a GeoDjango application::
|
|
|
|
# This is an auto-generated Django model module created by ogrinspect.
|
|
from django.contrib.gis.db import models
|
|
|
|
class WorldBorder(models.Model):
|
|
fips = models.CharField(max_length=2)
|
|
iso2 = models.CharField(max_length=2)
|
|
iso3 = models.CharField(max_length=3)
|
|
un = models.IntegerField()
|
|
name = models.CharField(max_length=50)
|
|
area = models.IntegerField()
|
|
pop2005 = models.IntegerField()
|
|
region = models.IntegerField()
|
|
subregion = models.IntegerField()
|
|
lon = models.FloatField()
|
|
lat = models.FloatField()
|
|
geom = models.MultiPolygonField(srid=4326)
|
|
objects = models.GeoManager()
|
|
|
|
# Auto-generated `LayerMapping` dictionary for WorldBorder model
|
|
worldborders_mapping = {
|
|
'fips' : 'FIPS',
|
|
'iso2' : 'ISO2',
|
|
'iso3' : 'ISO3',
|
|
'un' : 'UN',
|
|
'name' : 'NAME',
|
|
'area' : 'AREA',
|
|
'pop2005' : 'POP2005',
|
|
'region' : 'REGION',
|
|
'subregion' : 'SUBREGION',
|
|
'lon' : 'LON',
|
|
'lat' : 'LAT',
|
|
'geom' : 'MULTIPOLYGON',
|
|
}
|
|
|
|
Spatial Queries
|
|
===============
|
|
|
|
Spatial Lookups
|
|
---------------
|
|
GeoDjango extends the Django ORM and allows the use of spatial lookups.
|
|
Let's do an example where we find the ``WorldBorder`` model that contains
|
|
a point. First, fire up the management shell:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py shell
|
|
|
|
Now, define a point of interest [#]_::
|
|
|
|
>>> pnt_wkt = 'POINT(-95.3385 29.7245)'
|
|
|
|
The ``pnt_wkt`` string represents the point at -95.3385 degrees longitude,
|
|
and 29.7245 degrees latitude. The geometry is in a format known as
|
|
Well Known Text (WKT), an open standard issued by the Open Geospatial
|
|
Consortium (OGC). [#]_ Import the ``WorldBorder`` model, and perform
|
|
a ``contains`` lookup using the ``pnt_wkt`` as the parameter::
|
|
|
|
>>> from world.models import WorldBorder
|
|
>>> qs = WorldBorder.objects.filter(mpoly__contains=pnt_wkt)
|
|
>>> qs
|
|
[<WorldBorder: United States>]
|
|
|
|
Here we retrieved a ``GeoQuerySet`` that has only one model: the one
|
|
for the United States (which is what we would expect). Similarly,
|
|
a :ref:`GEOS geometry object <ref-geos>` may also be used -- here the
|
|
``intersects`` spatial lookup is combined with the ``get`` method to retrieve
|
|
only the ``WorldBorder`` instance for San Marino instead of a queryset::
|
|
|
|
>>> from django.contrib.gis.geos import Point
|
|
>>> pnt = Point(12.4604, 43.9420)
|
|
>>> sm = WorldBorder.objects.get(mpoly__intersects=pnt)
|
|
>>> sm
|
|
<WorldBorder: San Marino>
|
|
|
|
The ``contains`` and ``intersects`` lookups are just a subset of what's
|
|
available -- the :ref:`ref-gis-db-api` documentation has more.
|
|
|
|
Automatic Spatial Transformations
|
|
---------------------------------
|
|
When querying the spatial database GeoDjango automatically transforms
|
|
geometries if they're in a different coordinate system. In the following
|
|
example, the coordinate will be expressed in terms of `EPSG SRID 32140`__,
|
|
a coordinate system specific to south Texas **only** and in units of
|
|
**meters** and not degrees::
|
|
|
|
>>> from django.contrib.gis.geos import *
|
|
>>> pnt = Point(954158.1, 4215137.1, srid=32140)
|
|
|
|
Note that ``pnt`` may also constructed with EWKT, an "extended" form of
|
|
WKT that includes the SRID::
|
|
|
|
>>> pnt = GEOSGeometry('SRID=32140;POINT(954158.1 4215137.1)')
|
|
|
|
When using GeoDjango's ORM, it will automatically wrap geometry values
|
|
in transformation SQL, allowing the developer to work at a higher level
|
|
of abstraction::
|
|
|
|
>>> qs = WorldBorder.objects.filter(mpoly__intersects=pnt)
|
|
>>> print qs.query # Generating the SQL
|
|
SELECT "world_worldborders"."id", "world_worldborders"."name", "world_worldborders"."area",
|
|
"world_worldborders"."pop2005", "world_worldborders"."fips", "world_worldborders"."iso2",
|
|
"world_worldborders"."iso3", "world_worldborders"."un", "world_worldborders"."region",
|
|
"world_worldborders"."subregion", "world_worldborders"."lon", "world_worldborders"."lat",
|
|
"world_worldborders"."mpoly" FROM "world_worldborders"
|
|
WHERE ST_Intersects("world_worldborders"."mpoly", ST_Transform(%s, 4326))
|
|
>>> qs # printing evaluates the queryset
|
|
[<WorldBorder: United States>]
|
|
|
|
__ http://spatialreference.org/ref/epsg/32140/
|
|
|
|
Lazy Geometries
|
|
---------------
|
|
Geometries come to GeoDjango in a standardized textual representation. Upon
|
|
access of the geometry field, GeoDjango creates a `GEOS geometry object
|
|
<ref-geos>`, exposing powerful functionality, such as serialization properties
|
|
for popular geospatial formats::
|
|
|
|
>>> sm = WorldBorder.objects.get(name='San Marino')
|
|
>>> sm.mpoly
|
|
<MultiPolygon object at 0x24c6798>
|
|
>>> sm.mpoly.wkt # WKT
|
|
MULTIPOLYGON (((12.4157980000000006 43.9579540000000009, 12.4505540000000003 43.9797209999999978, ...
|
|
>>> sm.mpoly.wkb # WKB (as Python binary buffer)
|
|
<read-only buffer for 0x1fe2c70, size -1, offset 0 at 0x2564c40>
|
|
>>> sm.mpoly.geojson # GeoJSON (requires GDAL)
|
|
'{ "type": "MultiPolygon", "coordinates": [ [ [ [ 12.415798, 43.957954 ], [ 12.450554, 43.979721 ], ...
|
|
|
|
This includes access to all of the advanced geometric operations provided by
|
|
the GEOS library::
|
|
|
|
>>> pnt = Point(12.4604, 43.9420)
|
|
>>> sm.mpoly.contains(pnt)
|
|
True
|
|
>>> pnt.contains(sm.mpoly)
|
|
False
|
|
|
|
``GeoQuerySet`` Methods
|
|
-----------------------
|
|
|
|
|
|
Putting your data on the map
|
|
============================
|
|
|
|
Google
|
|
------
|
|
|
|
Geographic Admin
|
|
----------------
|
|
|
|
GeoDjango extends :doc:`Django's admin application </ref/contrib/admin/index>`
|
|
to enable support for editing geometry fields.
|
|
|
|
Basics
|
|
^^^^^^
|
|
|
|
GeoDjango also supplements the Django admin by allowing users to create
|
|
and modify geometries on a JavaScript slippy map (powered by `OpenLayers`_).
|
|
|
|
Let's dive in again -- create a file called ``admin.py`` inside the
|
|
``world`` application, and insert the following::
|
|
|
|
from django.contrib.gis import admin
|
|
from models import WorldBorder
|
|
|
|
admin.site.register(WorldBorder, admin.GeoModelAdmin)
|
|
|
|
Next, edit your ``urls.py`` in the ``geodjango`` project folder to look
|
|
as follows::
|
|
|
|
from django.conf.urls import patterns, url, include
|
|
from django.contrib.gis import admin
|
|
|
|
admin.autodiscover()
|
|
|
|
urlpatterns = patterns('',
|
|
(r'^admin/', include(admin.site.urls)),
|
|
)
|
|
|
|
Start up the Django development server:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py runserver
|
|
|
|
Finally, browse to ``http://localhost:8000/admin/``, and log in with the admin
|
|
user created after running ``syncdb``. Browse to any of the ``WorldBorder``
|
|
entries -- the borders may be edited by clicking on a polygon and dragging
|
|
the vertexes to the desired position.
|
|
|
|
.. _OpenLayers: http://openlayers.org/
|
|
.. _Open Street Map: http://openstreetmap.org/
|
|
.. _Vector Map Level 0: http://earth-info.nga.mil/publications/vmap0.html
|
|
.. _Metacarta: http://metacarta.com
|
|
|
|
.. _osmgeoadmin-intro:
|
|
|
|
``OSMGeoAdmin``
|
|
^^^^^^^^^^^^^^^
|
|
|
|
With the :class:`~django.contrib.gis.admin.OSMGeoAdmin`, GeoDjango uses
|
|
a `Open Street Map`_ layer in the admin.
|
|
This provides more context (including street and thoroughfare details) than
|
|
available with the :class:`~django.contrib.gis.admin.GeoModelAdmin`
|
|
(which uses the `Vector Map Level 0`_ WMS data set hosted at `Metacarta`_).
|
|
|
|
First, there are some important requirements and limitations:
|
|
|
|
* :class:`~django.contrib.gis.admin.OSMGeoAdmin` requires that the
|
|
:ref:`spherical mercator projection be added <addgoogleprojection>`
|
|
to the to be added to the ``spatial_ref_sys`` table (PostGIS 1.3 and
|
|
below, only).
|
|
* The PROJ.4 datum shifting files must be installed (see the
|
|
:ref:`PROJ.4 installation instructions <proj4>` for more details).
|
|
|
|
If you meet these requirements, then just substitute in the ``OSMGeoAdmin``
|
|
option class in your ``admin.py`` file::
|
|
|
|
admin.site.register(WorldBorder, admin.OSMGeoAdmin)
|
|
|
|
.. rubric:: Footnotes
|
|
|
|
.. [#] Special thanks to Bjørn Sandvik of `thematicmapping.org <http://thematicmapping.org>`_ for providing and maintaining this data set.
|
|
.. [#] GeoDjango basic apps was written by Dane Springmeyer, Josh Livni, and Christopher Schmidt.
|
|
.. [#] Here the point is for the `University of Houston Law Center <http://www.law.uh.edu/>`_.
|
|
.. [#] Open Geospatial Consortium, Inc., `OpenGIS Simple Feature Specification For SQL <http://www.opengis.org/docs/99-049.pdf>`_, Document 99-049.
|