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Spatial Data and GeoDjango

Bruno Renié

EuroPython 2011

Mobile Nuggets

Prerequisites: Django knowledge

GIS concepts

GeoDjango

Writing a GIS app

➀

GIS concepts

GIS

Geographic Information Systems

Coordinate Systems

Different ways to represent spatial data

Geodetic

Coordinates = longitude / latitude

geodetic

datum: ellipsoidal approximation of the earth's surface. E.g. WGS 84

Projected

Way to represent the curved surface on a flat surface
Compromises on distortion

Cylindrical

Planar

Conical

Projections

SRID, Spatial Reference ID
spatialreference.org

WGS 84: 4326

Spherical Mercator: 900913 (now 3857) …

SELECT COUNT(*) from spatial_ref_sys: 3749

Standards

Open Geospatial Consortium

SQL

WKT, GeoJSON, KML, GML, WMS…

Geometries

geometries

Geometry, GeometryCollection

Representation

WKB

WKT

POINT (30 10)

LINESTRING (30 10, 10 30, 40 40)

GEOMETRYCOLLECTION(POINT(4 6), LINESTRING(4 6,7 10))

GeoJSON

{"type": "Point", "coordinates": [30, 10]}

➁

GeoDjango

Started by Justin Bronn in 2006-2007
Merged into Django in 2008
django.contrib.gis

Requirements

Python + ctypes
gdal, geos and proj.4 C libraries
spatial database

Spatial backends

django.contrib.gis.db.backends

SpatiaLite
MySQL
Oracle
PostGIS

Use PostGIS*

*friends don't let friends use anything else

Geographic Admin
GEOS / GDAL

django.contrib.gis.{geos,gdal}

DataSource / LayerMapping
Serialization (KML, GeoJSON, GeoRSS…)

➂

Writing a game with contrib.gis

Typewar

game

Import countries data
Disply a random country's shape
Re-display it, on a map

INSTALLED_APPS += (
    'django.contrib.gis',
)

DATABASES = {'default': {
    'ENGINE': 'django.contrib.gis.db.backends.postgis',
    # '...' ...,
}}

$ createdb -T template_postgis -E UTF8 europythongame

$ ./manage.py startapp countries

World Borders data

thematicmapping.org/downloads
Shapefile

ogrinspect

$ ./manage.py ogrinspect WORLD_BORDERS.shp Country \
    --srid=4326 --mapping --multi-geom > coutries/models.py

from django.contrib.gis.db import models

class Country(models.Model):
    fips = models.CharField('FIPS Code', max_length=2)
    iso2 = models.CharField('2 Digit ISO', max_length=2)
    iso3 = models.CharField('3 Digit ISO', max_length=3)
    un = models.IntegerField('United Nations Code')
    name = models.CharField('Name', max_length=50)
    area = models.IntegerField()
    pop2005 = models.IntegerField('Population in 2005')
    region = models.IntegerField('Region Code')
    subregion = models.IntegerField('Sub-Region Code')
    lon = models.FloatField()
    lat = models.FloatField()

    geom = models.MultiPolygonField(srid=4326)

    objects = models.GeoManager()

from django.contrib.gis.db import models

class Country(models.Model):
    # ...
    geom = models.MultiPolygonField(srid=4326)

    objects = models.GeoManager()

country_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',
}

from django.contrib.gis.utils import LayerMapping

lm = LayerMapping(Country, 'TM_WORLD_BORDERS-0.3.shp',
                  country_mapping,
                  encoding='iso-8859-1')

lm.save(verbose=True)

Admin

GeoModelAdmin


from django.contrib.gis import admin
from coutries.models import Country

admin.site.register(Country, admin.GeoModelAdmin)
admin.site.register(Country, admin.OSMGeoAdmin)

django-floppyforms / olWidget

Floppyforms

pip install django-floppyforms
INSTALLED_APPS += ('floppyforms',)
import floppyforms as forms

GeoDjango widgets

Base widgets: map backends (OSM, GMaps, ...)
Geometry-specific widgets
Inherit from both

import floppyforms as forms

class MultiPolygonWidget(forms.gis.MultiPolygonWidget,
                         forms.gis.BaseOsmWidget):
    pass

from countries.models import Country

class CountryForm(forms.ModelForm):

    class Meta:
        model = Country
        widgets = {
            'geom': MultiPolygonWidget,
        }

from django.contrib import admin

class CountryAdmin(admin.ModelAdmin):
    form = CountryForm

admin.site.register(Country, CountryAdmin)

Spatial queries

>>> from django.contrib.gis.geos import Point
>>> from countries.models import Country

>>> p = Point(11.27, 43.77)
>>> Country.objects.filter(mpoly__contains=p)
[<Country: Italy>]

Spatial queries

>>> Country.objects.distance(p).order_by('distance')[:5]

[<Country: Italy>, <Country: San Marino>, <Country: France>,
<Country: Holy See (Vatican City)>, <Country: Croatia>]

Spatial queries

it = Country.objects.get(name='Italy')

# This is expensive
>>> Country.objects.distance(it.mpoly).order_by('distance')[:5]

[<Country: France>, <Country: San Marino>, <Country: Austria>,
<Country: Slovenia>, <Country: Italy>]

Spatial queries

https://docs.djangoproject.com/en/dev/ref/contrib/gis/db-api/

game

Mapping Frameworks

OpenLayers
Google Maps
Leaflet
Polymaps
Tile5

SVG

ct = Country.objects.order_by('?')

<script type="text/javascript"
        src="OpenLayers.js"></script>

<div id="map"></div>

<textarea class="hidden">
    {{ ct.geom.geojson|safe }}
</textarea>

var map = new OpenLayers.Map({
    div: "map",
    projection: "EPSG:900913",
    maxExtent: new OpenLayers.Bounds(-20037508,
                   -20037508,20037508,20037508),
    maxResolution: 156543.0339,
    units: 'm',
    controls: []
}),

parser = new OpenLayers.Format.GeoJSON();
features = parser.read($('textarea').innerHTML);

vector = new OpenLayers.Layer.Vector('Country'),
map.addLayer(vector);
map.setBaseLayer(vector);

var src = new OpenLayers.Projection('EPSG:4326');
var dst = map.getProjectionObject();

for (var i=0; i<features.length; i++) {
    feature = features[i];
    features.geometry.transform(src, dst);
}

vector.addFeatures(features);
map.zoomToExtent(vector.getDataExtent());

import floppyforms as forms

class ReadOnlyWidget(forms.gis.MultiPolygonWidget,
                     forms.gis.BaseOsmWidget):
    template_name = 'questions/widget.html'

class CountryForm(forms.Form):
    country = forms.gis.MultiPolygonField(
        widget=ReadOnlyWidget,
    )

{% extends "floppyforms/gis/osm.html" %}

{% block options %}{{ block.super }}

options['modifiable'] = false;

{% endblock %}

form = CountryForm(
    initial={
        'country': previous.country.geom,
    },
)

{{ form.media }}
{{ form }}

Spatial Data and GeoDjango

Bruno Renié

EuroPython 2011

Prerequisites: Django knowledge

GIS concepts

GeoDjango

Writing a GIS app

➀

GIS concepts

GIS

Coordinate Systems

Geodetic

datum: ellipsoidal approximation of the earth's surface. E.g. WGS 84

Projected

Projections

WGS 84: 4326

Spherical Mercator: 900913 (now 3857) …

Standards

SQL

WKT, GeoJSON, KML, GML, WMS…

Geometries

Geometry, GeometryCollection

Representation

WKB

WKT

POINT (30 10)

LINESTRING (30 10, 10 30, 40 40)

GEOMETRYCOLLECTION(POINT(4 6), LINESTRING(4 6,7 10))

GeoJSON

{"type": "Point", "coordinates": [30, 10]}

➁

GeoDjango

Requirements

Spatial backends

django.contrib.gis.db.backends

Use PostGIS*

*friends don't let friends use anything else

django.contrib.gis.{geos,gdal}

➂

Writing a game with contrib.gis

Typewar

World Borders data

ogrinspect

Admin

GeoModelAdmin

django-floppyforms / olWidget

Floppyforms

GeoDjango widgets

Spatial queries

Spatial queries

Spatial queries

Spatial queries

Mapping Frameworks

SVG

Recap

game.bruno.im

Going further

github.com/brutasse/geogame

@brutasse

Questions!