Check distances with latitude and longitude using PostgreSQL special indexes. This gem enables your model to query the database using the earthdistance extension. This should be much faster than using trigonometry functions over standard indexes.
Postgresql 9.1+ with contrib and Rails 3.1+
On Ubuntu, this is easy:
sudo apt-get install postgresql-contrib-9.1
On Mac you have a couple of options:
- the binary package kindly provided by EnterpriseDB
- Homebrew’s Postgres installation also includes the contrib packages:
brew install postgres
Earthdistance is a PostgreSQL contrib module, check it out first.
Then, just add this to your Gemfile:
And run your bundler:
Now you need to create a migration that adds earthdistance support for your PostgreSQL database:
rails g earth_distance:setup
Now let's add some gist indexes to make queries ultra-fast. For the model Place we could create an index over the lat and lng fields:
rails g migration add_index_to_places
Edit the created migration:
class AddIndexToPlaces < ActiveRecord::Migration def up add_earthdistance_index :places end def down remove_earthdistance_index :places end end
This will create the index with a SQL like this:
CREATE INDEX places_earthdistance_ix ON places USING GIST (ll_to_earth(lat, lng));
This gem only provides a custom serialization coder. If you want to use it just put in your Gemfile:
Now add a line (for each earthdistance column) on the model you have your earthdistance columns. Assuming a model called Person, with a data field on it, the code should look like:
class Place < ActiveRecord::Base acts_as_geolocated end
This way, you will automatically look for columns with names such as lat/latitude and lng/longitude. But you can use alternative names passing them as:
class Place < ActiveRecord::Base acts_as_geolocated lat: 'latitude_column_name', lng: 'longitude_column_name' end
Querying the database
To query for all places within a given radius of 100 meters from the origin -22.951916,-43.210487 just use:
Place.within_radius(100, -22.951916, -43.210487).all
You can also order the records based on the distance from a point
within_radius query performs two checks: first against the bounding box, followed by computing the exact distance for
all contained elements. The latter might be computationally expensive for big ranges.
So if precision is not an issue but query speed is, you might want to query against the bounding box only:
Select the distance from a point:
point = [-22.951916, -43.210487] closest = Place.within_radius(100, *point).order_by_distance(*point).selecting_distance_from(*point).first closest.distance
To have earthdistance enabled when you load your database schema (as happens in rake db:test:prepare), you have two options.
The first option is creating a template database with earthdistance installed and set the template option in database.yml to that database.
The second option is to uncomment or add the following line in config/application.rb
config.active_record.schema_format = :sql
This will change your schema dumps from Ruby to SQL. If you're unsure about the implications of this change, we suggest reading this Rails Guide.
You can use issues in github for that. Or else you can reach us at twitter: @dbiazus
Note on Patches/Pull Requests
- Fork the project.
- Make your feature addition or bug fix.
- Add tests for it. This is important so I don’t break it in a future version unintentionally.
- Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
- Send me a pull request. Bonus points for topic branches.
Copyright © 2010 Diogo Biazus. See LICENSE for details.