Geokit Rails

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COMMUNICATION

  • If you need help, use Stack Overflow. (Tag 'geokit' and we'll be alerted)
  • If you found a bug, use GitHub issues.
  • If you have an idea, use GitHub issues.
  • If you'd like to ask a general question, use GitHub issues.
  • If you want to contribute, submit a pull request.

INSTALLATION

Geokit for Rails consists of a generic Gem (geokit) and a Rails plugin (geokit-rails).

Make sure you use a version >= 3.0 of Rails.

You just have to add the 'geokit-rails' gem to your Gemfile

gem 'geokit-rails'

Then tell bundler to update the gems :

$ bundle install

Last, consult the important post-installation notes section at the end of this document.

If you want to use geokit-rails in a Rails 2 application, just use the good old plugin (geokit-rails).

FEATURE SUMMARY

Geokit provides key functionality for location-oriented Rails applications:

  • Distance calculations, for both flat and spherical environments. For example, given the location of two points on the earth, you can calculate the miles/Km between them.
  • ActiveRecord distance-based finders. For example, you can find all the points in your database within a 50-mile radius.
  • IP-based location lookup utilizing hostip.info. Provide an IP address, and get city name and latitude/longitude in return
  • A before_filter helper to geocoder the user's location based on IP address, and retain the location in a cookie.
  • Geocoding from multiple providers. It provides a fail-over mechanism, in case your input fails to geocode in one service. Geocoding is provided by the Geokit gem, which you must have installed

The goal of this plugin is to provide the common functionality for location-oriented applications (geocoding, location lookup, distance calculation) in an easy-to-use package.

A NOTE ON TERMINOLOGY

Throughout the code and API, latitude and longitude are referred to as lat and lng. We've found over the long term the abbreviation saves lots of typing time.

LOCATION QUERIES

MAKING A MODEL MAPPABLE

To get started, just specify an ActiveRecord class as acts_as_mappable:

class Location < ActiveRecord::Base
  acts_as_mappable
end

There are some defaults you can override:

class Location < ActiveRecord::Base
  acts_as_mappable :default_units => :miles,
                   :default_formula => :sphere,
                   :distance_field_name => :distance,
                   :lat_column_name => :lat,
                   :lng_column_name => :lng
end

The optional parameters are units, formula, and distance_field_name. Values for units can be :miles, :kms (kilometers), or :nms (nautical miles), with :miles as the default. Values for formula can be :sphere or :flat with :sphere as the default. :sphere gives you Haversine calculations, while :flat gives the Pythagoreum Theory. These defaults persist through out the gem.

The plug-in creates a calculated distance field on AR instances that have been retrieved through a Geokit location query. By default, these fields are known as "distance" but this can be changed through the :distance_field_name key.

You can also define alternative column names for latitude and longitude using the :lat_column_name and :lng_column_name keys. The defaults are lat and lng respectively.

NEW SCOPES TO USE

Once you've specified acts_as_mappable, a few scopes are available :

  • within and beyond find records within or beyond a certain distance from the origin point.
  • in_range finds records within a certain distance range from the origin point.
  • in_bounds finds records within a rectangle on the map
  • closest and farthest find the closest or farthest record from the origin point
  • by_distance finds records ordered by distance from the origin point

All these scopes are the porcelain for a lower level scope named geo_scope that take a hash of options. Their first parameter is simply one of the possible options, without the name

A few examples :

Location.within(5, :origin => @somewhere)
# is the same as
Location.geo_scope(:within => 5, :origin => @somewhere)

Location.in_range(2..5, :origin => @somewhere)
# is the same as
Location.geo_scope(:range => 2..5, :origin => @somewhere)

Location.in_bounds([@south_west_point, @north_east_point], :origin => @somewhere)
# is the same as
Location.geo_scope(:bounds => [@south_west_point, @north_east_point], :origin => @somewhere)

The options can be :

:origin as a two-element array of latitude/longitude:

Location.geo_scope(:origin => [37.792,-122.393])

:origin as a geocodeable string:

Location.geo_scope(:origin => '100 Spear st, San Francisco, CA')

:origin as an object which responds to lat and lng methods, or latitude and longitude methods, or whatever methods you have specified for lng_column_name and lat_column_name:

Location.geo_scope(:origin => my_store)
# my_store.lat and my_store.lng methods exist

:units or :formula can be used to override the default values in a specific query

Location.within(5, :units => :kms, :origin => @somewhere)
# it will get the records within 5 kilometers instead of 5 miles

:range as a native Ruby range

:bounds as an array of two elements : the south/west point and the north/east point.

@sw = Geokit::LatLng.new(32.91663,-96.982841)
@ne = Geokit::LatLng.new(32.96302,-96.919495)
@somewhere = Location.find(123456)
Location.geo_scope(:bounds => [@sw, @ne], :origin => @somewhere)

:bounds as a Geokit::Bounds object

@bounds = Geokit::Bounds.new([32.91663,-96.982841], [32.96302,-96.919495])
@somewhere = Location.find(123456)
Location.geo_scope(:bounds => [@sw, @ne], :origin => @somewhere)

When using a point of reference or bounds, you leverage the power of Geokit to build this objects. Basically, if Geokit can make a Geokit::Point or a Geokit::Bounds with what you give to it, you're good to go.

FIND BY SQL

Finally, if all that is desired is the raw SQL for distance calculations, you can use the following:

Location.distance_sql(origin, units = default_units, formula = default_formula)

Thereafter, you are free to use it in find_by_sql as you wish.

CHAINABILITY

You can then chain these scope with any other or use a "calling" method like first, all, count, …

Location.within(5, :origin => @somewhere).all
Location.within(5, :origin => @somewhere).count
Location.geo_scope(:origin => [37.792,-122.393]).first

You can add order clauses in the chain as for any ActiveRecord query

Location.within(5, :origin => @somewhere).order('nbr_seats ASC')

You can even sort by distance (use the same name as specified in the model class)

Location.within(5, :origin => @somewhere).order('distance DESC, nbr_seats ASC')

Idem for the limit clause. In fact, closest and farthest are defined like this :

def closest(options = {})
  geo_scope(options).order("#{distance_column_name} asc").limit(1)
end
def farthest(options = {})
  geo_scope(options).order("#{distance_column_name} desc").limit(1)
end

Important caveat

In the current version of geokit-rails, it is not possible to add a where clause using the distance column. I've tried many different ways to do this and didn't get it working.

One would expect to build a query like this :

scoped  = Location.geo_scope(:origin => @somewhere)
scoped  = scoped.where('distance <= 5)
results = scoped.all

This is not possible right now, it must be done in a single step like this :

scoped  = Location.within(5, :origin => @somewhere)
results = scoped.all

Every good idea that would help achieve this is very much welcome.

FINDING WITHIN A BOUNDING BOX

If you are displaying points on a map, you probably need to query for whatever falls within the rectangular bounds of the map:

Store.in_bounds([sw_point,ne_point]).all

The input to bounds can be an array with the two points or a Bounds object. However you provide them, the order should always be the southwest corner, northeast corner of the rectangle. Typically, you will be getting the sw_point and ne_point from a map that is displayed on a web page.

If you need to calculate the bounding box from a point and radius, you can do that:

bounds = Geokit::Bounds.from_point_and_radius(home,5)
Store.in_bounds(bounds).all

What is following is from the previous geokit-rails plugin.

It has not been tested with Rails 3 nor with this version of the gem. Most of it should work, but it is not sure

USING INCLUDES

You can use includes along with your distance finders:

stores = Store.within(5, :origin=>home).includes([:reviews,:cities]).order('distance asc').all

However, ActiveRecord drops the calculated distance column when you use include. So, if you need to use the distance column, you'll have to re-calculate it post-query in Ruby:

stores.sort_by{|s| s.distance_to(home)}

In this case, you may want to just use the bounding box condition alone in your SQL (there's no use calculating the distance twice):

bounds=Geokit::Bounds.from_point_and_radius(home,5)
stores=Store.includes([:reviews,:cities]).in_bounds(bounds)
stores.sort_by{|s| s.distance_to(home)}

USING :through

You can also specify a model as mappable "through" another associated model. In other words, that associated model is the actual mappable model with "lat" and "lng" attributes, but this "through" model can still utilize all of the above find methods to search for records.

class Location < ActiveRecord::Base
  belongs_to :locatable, :polymorphic => true
  acts_as_mappable
end

class Company < ActiveRecord::Base
  has_one :location, :as => :locatable  # also works for belongs_to associations
  acts_as_mappable :through => :location
end

Then you can still call:

Company.within(distance, :origin => @somewhere)

You can also give :through a hash if your location is nested deep. For example, given:

class House
  acts_as_mappable
end

class Family
  belongs_to :house
end

class Person
  belongs_to :family
  acts_as_mappable :through => { :family => :house }
end

Remember that the notes above about USING INCLUDES apply to the results from this find, since an include is automatically used.

IP GEOCODING

You can obtain the location for an IP at any time using the geocoder as in the following example:

location = IpGeocoder.geocode('12.215.42.19')

where Location is a GeoLoc instance containing the latitude, longitude, city, state, and country code. Also, the success value is true.

If the IP cannot be geocoded, a GeoLoc instance is returned with a success value of false.

It should be noted that the IP address needs to be visible to the Rails application. In other words, you need to ensure that the requesting IP address is forwarded by any front-end servers that are out in front of the Rails app. Otherwise, the IP will always be that of the front-end server.

The Multi-Geocoder will also geocode IP addresses and provide failover among multiple IP geocoders. Just pass in an IP address for the parameter instead of a street address. Eg:

location = Geocoders::MultiGeocoder.geocode('12.215.42.19')

The MultiGeocoder class requires 2 configuration setting for the provider order. Ordering is done through Geokit::Geocoders::provider_order and Geokit::Geocoders::ip_provider_order, found in config/initializers/geokit_config.rb. If you don't already have a geokit_config.rb file, the plugin creates one when it is first installed.

IP GEOCODING HELPER

A class method called geocode_ip_address has been mixed into the ActionController::Base. This enables before_filter style lookup of the IP address. Since it is a filter, it can accept any of the available filter options.

Usage is as below:

class LocationAwareController < ActionController::Base
  geocode_ip_address
end

A first-time lookup will result in the GeoLoc class being stored in the session as :geo_location as well as in a cookie called :geo_session. Subsequent lookups will use the session value if it exists or the cookie value if it doesn't exist. The last resort is to make a call to the web service. Clients are free to manage the cookie as they wish.

The intent of this feature is to be able to provide a good guess as to a new visitor's location.

INTEGRATED FIND AND GEOCODING

Geocoding has been integrated with the finders enabling you to pass a physical address or an IP address. This would look the following:

Location.farthest(:origin => '217.15.10.9')
Location.farthest(:origin => 'Irving, TX')

where the IP or physical address would be geocoded to a location and then the resulting latitude and longitude coordinates would be used in the find. This is not expected to be common usage, but it can be done nevertheless.

ADDRESS GEOCODING

Geocoding is provided by the Geokit gem, which is required for this plugin. See the top of this file for instructions on installing the Geokit gem.

Geokit can geocode addresses using multiple geocodeing web services. Geokit supports services like Google, Yahoo, and Geocoder.us, and more -- see the Geokit gem API for a complete list.

These geocoder services are made available through the following classes: GoogleGeocoder, YahooGeocoder, UsGeocoder, CaGeocoder, and GeonamesGeocoder. Further, an additional geocoder class called MultiGeocoder incorporates an ordered failover sequence to increase the probability of successful geocoding.

All classes are called using the following signature:

include Geokit::Geocoders
location = XxxGeocoder.geocode(address)

where you replace Xxx Geocoder with the appropriate class. A GeoLoc instance is the result of the call. This class has a "success" attribute which will be true if a successful geocoding occurred. If successful, the lat and lng properties will be populated.

Geocoders are named with the convention NameGeocoder. This naming convention enables Geocoder to auto-detect its sub-classes in order to create methods called name_geocoder(address) so that all geocoders can be called through the base class. This is done purely for convenience; the individual geocoder classes are expected to be used independently.

The MultiGeocoder class requires the configuration of a provider order which dictates what order to use the various geocoders. Ordering is done through Geokit::Geocoders::provider_order, found in config/initializers/geokit_config.rb.

If you don't already have a geokit_config.rb file, the plugin creates one when it is first installed.

Make sure your failover configuration matches the usage characteristics of your application -- for example, if you routinely get bogus input to geocode, your code will be much slower if you have to failover among multiple geocoders before determining that the input was in fact bogus.

The Geocoder.geocode method returns a GeoLoc object. Basic usage:

loc=Geocoder.geocode('100 Spear St, San Francisco, CA')
if loc.success
  puts loc.lat
  puts loc.lng
  puts loc.full_address
end

REVERSE GEOCODING

Currently, only the Google Geocoder supports reverse geocoding. Pass the lat/lng as a string, array or LatLng instance:

res=Geokit::Geocoders::GoogleGeocoder.reverse_geocode "37.791821,-122.394679"
=> #<Geokit::GeoLoc:0x558ed0 ...
res.full_address "101-115 Main St, San Francisco, CA 94105, USA"

The address will usually appear as a range, as it does in the above example.

INTEGRATED FIND WITH ADDRESS GEOCODING

Just has you can pass an IP address directly into an ActiveRecord finder as the origin, you can also pass a physical address as the origin:

Location.find_closest(:origin => '100 Spear st, San Francisco, CA')

where the physical address would be geocoded to a location and then the resulting latitude and longitude coordinates would be used in the find.

Note that if the address fails to geocode, the find method will raise an ActiveRecord::GeocodeError you must be prepared to catch. Alternatively, You can geocoder the address beforehand, and pass the resulting lat/lng into the finder if successful.

Auto Geocoding

If your geocoding needs are simple, you can tell your model to automatically geocode itself on create:

class Store < ActiveRecord::Base
  acts_as_mappable :auto_geocode=>true
end

It takes two optional params:

class Store < ActiveRecord::Base
  acts_as_mappable :auto_geocode=>{:field=>:address, :error_message=>'Could not geocode address'}
end

. . . which is equivalent to:

class Store << ActiveRecord::Base
  acts_as_mappable
  before_validation :geocode_address, :on => :create

  private
  def geocode_address
    geo=Geokit::Geocoders::MultiGeocoder.geocode (address)
    errors.add(:address, "Could not Geocode address") if !geo.success
    self.lat, self.lng = geo.lat,geo.lng if geo.success
  end
end

If you need any more complicated geocoding behavior for your model, you should roll your own before_validate callback.

Distances, headings, endpoints, and midpoints

distance = home.distance_from(work, :units=>:miles)
heading  = home.heading_to(work) # result is in degrees, 0 is north
endpoint = home.endpoint(90,2)  # two miles due east
midpoint = home.midpoint_to(work)

Cool stuff you can do with bounds

bounds = Bounds.new(sw_point,ne_point)
bounds.contains?(home)
puts bounds.center

HOW TO . . .

A few quick examples to get you started ....

How to install the Geokit Rails plugin

(See the very top of this file)

How to find all stores within a 10-mile radius of a given lat/lng

  1. ensure your stores table has lat and lng columns with numeric or float datatypes to store your latitude/longitude

  2. use acts_as_mappable on your store model:

  3. class Store < ActiveRecord::Base
 acts_as_mappable
 ...
end

  4. finders now have extra capabilities:

  Store.find(:all, :origin =>[32.951613,-96.958444], :within=>10)

How to geocode an address

  1. configure your geocoder key(s) in config/initializers/geokit_config.rb

  2. also in geokit_config.rb, make sure that Geokit::Geocoders::provider_order reflects the geocoder(s). If you only want to use one geocoder, there should be only one symbol in the array. For example:

  Geokit::Geocoders::provider_order=[:google]
  1. Test it out in script/console
  include Geokit::Geocoders
  res = MultiGeocoder.geocode('100 Spear St, San Francisco, CA')
  puts res.lat
  puts res.lng
  puts res.full_address

... etc. The return type is GeoLoc, see the API for
all the methods you can call on it.

How to find all stores within 10 miles of a given address

  1. as above, ensure your table has the lat/lng columns, and you've applied acts_as_mappable to the Store model.

  2. configure and test out your geocoder, as above

  3. pass the address in under the :origin key

  Store.find(:all, :origin=>'100 Spear st, San Francisco, CA', :within=>10)
  1. you can also use a zipcode, or anything else that's geocodable:
  Store.find(:all, :origin=>'94117', :conditions=>'distance<10')

How to sort a query by distance from an origin

You now have access to a 'distance' column, and you can use it as you would any other column. For example:

Store.find(:all, :origin=>'94117', :order=>'distance')

How to sort elements of an array according to distance from a common point

Usually, you can do your sorting in the database as part of your find call. If you need to sort things post-query, you can do so:

stores = Store.all
stores.sort_by{|s| s.distance_to(home)}

Obviously, each of the items in the array must have a latitude/longitude so they can be sorted by distance.

Database indexes

MySQL can't create indexes on a calculated field such as those Geokit uses to calculate distance based on latitude/longitude values for a record. However, indexing the lat and lng columns does improve Geokit distance calculation performance since the lat and lng columns are used in a straight comparison for distance calculation. Assuming a Page model that is incorporating the Geokit plugin the migration would be as follows.

class AddIndexToPageLatAndLng < ActiveRecord::Migration

  def self.up
    add_index  :pages, [:lat, :lng]
  end

  def self.down
    remove_index  :pages, [:lat, :lng]
  end
end

Database Compatability

  • Geokit works with MySQL (tested with version 5.0.41), PostgreSQL (tested with version 8.2.6) and Microsoft SQL Server (tested with 2000).
  • Geokit is known to not work with Postgres versions under 8.1 -- it uses the least() funciton.

HIGH-LEVEL NOTES ON WHAT'S WHERE

acts_as_mappable.rb, as you'd expect, contains the ActsAsMappable module which gets mixed into your models to provide the location-based finder goodness.

ip_geocode_lookup.rb contains the before_filter helper method which enables auto lookup of the requesting IP address.

The Geokit gem provides the building blocks of distance-based operations:

The Mappable module, which provides basic distance calculation methods, i.e., calculating the distance between two points.

The LatLng class is a simple container for latitude and longitude, but it's made more powerful by mixing in the above-mentioned Mappable module -- therefore, you can calculate easily the distance between two LatLng objects with distance = first.distance_to(other)

GeoLoc represents an address or location which has been geocoded. You can get the city, zipcode, street address, etc. from a GeoLoc object. GeoLoc extends LatLng, so you also get lat/lng AND the Mappable module goodness for free.

IMPORTANT POST-INSTALLATION NOTES:

1. The configuration file: Geokit for Rails uses a configuration file in config/initializers. You must add your own keys for the various geocoding services if you want to use geocoding. If you need to refer to the original template again, see the assets/api_keys_template file.

2. The gem dependency: Geokit for Rails depends on the Geokit gem. Tell Rails about this dependency in config/environment.rb, within the initializer block: config.gem "geokit"