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Add support for PostgreSQL earthdistance extension to Django

Project description

Using PostgreSQL’s EarthDistance extension for django >= 1.8 (for older versions see with_djorm_expressions branch)*

Earthdistance allows to do fast geolocalized queries without using PostGIS

https://pypip.in/v/django-earthdistance/badge.png https://pypip.in/d/django-earthdistance/badge.png

Tested with python 2.7 and 3.3

Usage

Cube and EarthDistance extensions must be enabled in postgreSQL BD, so log in database using pgsql and install extensions:

=> create extension cube;
=> create extension earthdistance;

Filter by rows inside a circunference of radius r

from django.db import models

from django_earthdistance.models import EarthDistanceQuerySet

class MyModel(models.Model):
    latitute = models.FloatField()
    longitude = models.FloatField()

    objects = EarthDistanceQuerySet.as_manager()

# Define fields to query in DistanceExpression initialization
# search with lat=0.2546 and lon=-38.25 and distance 1500 meters
# use param `annotate` to set a custom field for the distance, `_ed_distance` as default

MyModel.objects.in_distance(1500, fields=['latitude', 'longitude'], points=[0.2546, -38.25])

Annotate each row returned by a query with distance between two points

from django_earthdistance.models import EarthDistance, LlToEarth

MyModel.objects.filter(....).annotate(
    distance=EarthDistance(
        LlToEarth([0.2546, -38.25]),
        LlToEarth(['latitude', 'longitude'])))

Optimizing perfomance with indexes

PostgreSQL allow to use GiST indexes with functions results, a good perfomance improvement is to store ll_to_earth results in an index, ll_to_earth is a function that calculates the position of a point on the surface of the earth (assuming earth is perfectly spherical)

-- Example MyModel table is app_mymodel and points columns are latitude and longitude
CREATE INDEX mymodel_location ON app_mymodel USING gist (ll_to_earth(latitude, longitude));

Also, using south is preferred, just add this migration to migrations/ folder and edit it to your needs, index will be created

class Migration(SchemaMigration):

    def forwards(self, orm):
        cursor = connection.cursor()
        cursor.execute("CREATE INDEX mymodel_location ON app_mymodel USING gist (ll_to_earth(latitude, longitude));")


    def backwards(self, orm):
        # Deleting field 'Venue.coords'
        cursor = connection.cursor()
        cursor.execute("DROP INDEX mymodel_location ON app_mymodel;")

Project details


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