geo-django

Running Django with PostGIS and geolocation libraries

Ovewview

Django

Django is a high-level web framework for building web applications in Python. It was first released in 2005 and has since become one of the most popular Python web frameworks, known for its flexibility, scalability, and ease of use.

Django provides a set of tools and libraries that help developers create web applications quickly and efficiently. It follows the Model-View-Controller (MVC) architectural pattern, but instead of using separate components for the Model, View, and Controller, Django uses a slightly different approach called Model-View-Template (MVT). In the MVT pattern, the Template component is responsible for rendering the HTML pages, while the Model component defines the database structure, and the View component handles the logic of the application.

Django is designed to be modular, which means that developers can use only the parts of the framework that they need, and they can add new functionality by using third-party packages or building their own reusable components. Django also includes built-in support for common web development tasks such as authentication, URL routing, form handling, and database migration.

PostGIS

PostGIS is an open-source extension for the PostgreSQL database management system that adds support for geospatial data. It allows users to store and manipulate spatial data such as points, lines, and polygons, and perform geospatial queries and analyses.

PostGIS provides a wide range of geospatial functions and operators that can be used to perform geometric and topological operations on spatial data, such as distance calculations, intersection tests, buffering, and simplification. It also supports various spatial data formats, such as Well-Known Text (WKT), Well-Known Binary (WKB), and GeoJSON, and can import and export data to and from other geospatial formats such as Shapefiles.

PostGIS is widely used in a variety of applications that deal with geospatial data, such as geographic information systems (GIS), location-based services, and web mapping. It is a powerful tool for managing and analyzing geospatial data within the context of a relational database, providing a scalable and flexible solution for storing and processing large amounts of spatial data.

Geo Django

GeoDjango is a geospatial web framework that extends Django, the popular Python web framework, with geospatial capabilities. It provides a set of tools and libraries that allow developers to build web applications that deal with geospatial data and perform geospatial queries and analyses.

GeoDjango includes the PostGIS extension for PostgreSQL, which allows users to store and manipulate geospatial data using a relational database. It also provides a set of Python APIs and utilities for working with geospatial data, such as the GeoDjango model fields for storing geometries and the GeoQuerySet API for performing spatial queries.

Leaflet

Leaflet is a popular open-source JavaScript library for building interactive maps and map-based applications. It provides a simple and flexible API for creating maps and adding various layers, markers, and popups to them.

When used with Django, Leaflet can be integrated into web applications to display and manipulate geospatial data. Django provides a set of tools and libraries for working with geospatial data, such as GeoDjango and the Django ORM, which can be used to store, retrieve, and manipulate geospatial data. Leaflet can then be used to render this geospatial data on a web page as an interactive map.

One way to use Leaflet in Django is to include the Leaflet JavaScript library in your Django project and use it to render a map on a web page. You can then use the Django ORM or a third-party package such as GeoDjango to retrieve geospatial data from a database and add it as markers or layers on the map.

There are also several third-party packages available for integrating Leaflet with Django, such as django-leaflet and django-geojson, which provide additional tools and utilities for working with geospatial data and Leaflet maps in Django.

Django Rest Framework

Django REST framework is a powerful toolkit for building Web APIs in Django. It provides a set of tools and utilities for building RESTful APIs, including serialization, authentication, pagination, and content negotiation.

With Django REST framework, developers can easily create APIs that communicate with other applications or services over the web. It supports both JSON and XML data formats, and provides a consistent and intuitive API for performing CRUD (Create, Retrieve, Update, Delete) operations on resources.

GDAL

GDAL (Geospatial Data Abstraction Library) is an open-source library for reading, writing, and manipulating geospatial data. It provides a set of tools and APIs for working with various raster and vector geospatial data formats, such as GeoTIFF, NetCDF, HDF, and Shapefile.

GeoTIFF

A GeoTIFF file is a standard file format for storing georeferenced raster data. It is a type of TIFF (Tagged Image File Format) file that includes additional geospatial metadata such as projection, coordinate system, and other spatial reference information.

A GeoTIFF file consists of one or more raster bands, where each band represents a different spectral channel or data layer. Each pixel in the raster is associated with a set of geographic coordinates that define its location on the Earth's surface. The geospatial metadata in the file allows software applications to interpret and manipulate the raster data in a spatial context, such as displaying it on a map or performing spatial analysis.

GeoTIFF files are widely used in various fields such as remote sensing, GIS (Geographic Information Systems), and cartography, and can contain a wide range of data types such as elevation data, satellite imagery, and land cover data. They are supported by many software applications and libraries, including GDAL (Geospatial Data Abstraction Library), QGIS, ArcGIS, and others.

SRID

A SRID (Spatial Reference ID) is a unique identifier that defines the coordinate system and projection of a geometry. It specifies the reference system in which the coordinates of the geometry are measured, and allows you to transform coordinates between different reference systems.

EWKT

EWKT (Extended Well-Known Text) is a text representation of a geometry that includes the SRID information. It is used to specify the spatial reference system of a geometry in text format.

References

• PostGIS
• Django Postgres
• Psycopg2
• GDAL
• PostGIS Docker tags

Architecture

File	Description
docker-compose.yml	Docker compose file.
manage.py	Django utility to manage the project.
cat/settings.py	Application settings file.
cat/urls.py	Routes settings file.
cat/wsgi.py	WSGI settings file.
core/apps.py	Core application configuration file.
core/fixtures/user.py	User sample data.
map/admin.py	Map application admin file.
map/models.py	Map application models file.
map/apps.py	Map application configuration file.
map/tests.py	Map application tests file.
map/views.py	Map application views.
map/fixtures/location.py	Location sample data.

Instructions

Starting a PostgreSQL database using Docker

docker-compose up

Installing all the dependencies

virtualenv -p "python3" .env
source .env/bin/activate
pip3 install -r requirements.txt

Applying migrations

python3 manage.py migrate --noinput

Load some test data

python manage.py loaddata core/fixtures/user.json
python manage.py loaddata map/fixtures/location.json

Starting the Django application locally

python3 manage.py runserver

Django version 4.2, using settings 'cat.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C

Create an admin

python3 manage.py shell

from django.contrib.auth.models import User
user = User()
user.username = 'test'
user.email = 'test@test.com'
user.set_password('test')
user.is_superuser = True
user.is_staff = True
user.save()

Login with username and password at http://127.0.0.1:8000/admin/login/?next=/admin/

Go to the Django admin

Check the Geospatial fields

In the Django shell, create a location object with a Point field:

>>> from django.contrib.gis.geos import Point
>>> from map.models import Location
>>> point = Point(0, 0)
>>> location = Location.objects.create(name='My Location', point=point)
>>> location.point.x
0.0
>>> location.point.y
0.0
>>> location.point.z
>>> location.point.srid
4326
>>> location.point.ewkt
'SRID=4326;POINT (0 0)'
>>> location.point.hex
b'010100000000000000000000000000000000000000'
>>> location.point.distance(Point(3, 4, 2))
5.0
>>> location.point.buffer(location.point.distance(Point(3, 4, 2)))
<Polygon object at 0x1176f5510>
>>> location.point.equals(Point(0, 0, 0))
True

In the Django shell, find locations within a certain distance of a point:

>>> from django.contrib.gis.measure import D
>>> from django.contrib.gis.geos import Point
>>> from map.models import Location
>>> locations = Location.objects.filter(point__distance_lte=(Point(1, 1), D(m=10000000000)))
>>> locations.count()
5

In the Django shell, find locations that intersect a polygon:

>>> from django.contrib.gis.geos import Polygon
>>> polygon = Polygon(((0, 0), (0, 10), (10, 10), (10, 0), (0, 0)))
>>> locations = Location.objects.filter(polygon__intersects=polygon)
>>> locations.count()
1

In the Django shell, get the centroid of a polygon

>>> from django.contrib.gis.geos import Polygon
>>> polygon = Polygon(((0, 0), (0, 10), (10, 10), (10, 0), (0, 0)))
>>> polygon.centroid.tuple
(5.0, 5.0)