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Geokit gem for Merb/ActiveRecord. Provides location-based goodness for your Merb app. Requires geokit-gem.
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README.markdown

INSTALLATION

Geokit consists of a Gem (geokit-gem) and a Merb plugin (geokit-merb).

First install the gem:

gem sources -a http://gems.github.com
sudo gem install andre-geokit

Next, install is plugin:

sudo gem install erudified-geokit-merb

And you're good to go! FYI, the gem stands alone (you can use it without the plugin), but the plugin requires the gem.

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 currently supports Google, Yahoo, Geocoder.us, and Geocoder.ca geocoders, and it provides a uniform response structure from all of them. It also provides a fail-over mechanism, in case your input fails to geocode in one service. Geocoding is provided buy 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.

DISTANCE CALCULATIONS AND QUERIES

If you want only distance calculation services, you need only mix in the Mappable module like so:

class Location
    include Geokit::Mappable
end

After doing so, you can do things like:

Location.distance_between(from, to) 

with optional parameters :units and :formula. Values for :units can be :miles or :kms 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 plug-in.

You can also do:

location.distance_to(other)

The real power and utility of the plug-in is in its query support. This is achieved through mixing into an ActiveRecord model object:

class Location < ActiveRecord::Base
    acts_as_mappable
end

The plug-in uses the above-mentioned defaults, but can be modified to use different units and a different formulae. This is done through the :default_units and :default_formula keys which accept the same values as mentioned above.

The plug-in creates a calculated column and potentially a calculated condition.
By default, these are known as "distance" but this can be changed through the :distance_field_name key.

So, an alternative invocation would look as below:

class Location < ActiveRecord::Base
   acts_as_mappable :default_units => :kms, 
                    :default_formula => :flat, 
                    :distance_field_name => :distance
end

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.

Thereafter, a set of finder methods are made available. Below are the different combinations:

Origin as a two-element array of latititude/longitude:

    find(:all, :origin => [37.792,-122.393])

Origin as a geocodeable string:

    find(:all, :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:

    find(:all, :origin=>my_store) # my_store.lat and my_store.lng methods exist

Often you will need to find within a certain distance. The prefered syntax is:

find(:all, :origin => @somewhere, :within => 5)

. . . however these syntaxes will also work:

find_within(5, :origin => @somewhere)
find(:all, :origin => @somewhere, :conditions => "distance < 5")

Note however that the third form should be avoided. With either of the first two, Geokit automatically adds a bounding box to speed up the radial query in the database. With the third form, it does not.

If you need to combine distance conditions with other conditions, you should do so like this:

find(:all, :origin => @somewhere, :within => 5, :conditions=>['state=?',state])

If :origin is not provided in the finder call, the find method works as normal. Further, the key is removed from the :options hash prior to invoking the superclass behavior.

Other convenience methods work intuitively and are as follows:

find_within(distance, :origin => @somewhere)
find_beyond(distance, :origin => @somewhere)
find_closest(:origin => @somewhere)
find_farthest(:origin => @somewhere)

where the options respect the defaults, but can be overridden if desired.

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

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

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

There are methods available to enable you to get the count based upon the find condition that you have provided. These all work similarly to the finders. So for instance:

count(:origin, :conditions => "distance < 5")
count_within(distance, :origin => @somewhere)
count_beyond(distance, :origin => @somewhere)

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.find :all, :bounds=>[sw_point,ne_point]

The input to :bounds can be 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=Bounds.from_point_and_radius(home,5)
Store.find :all, :bounds=>bounds

USING INCLUDES

You can use includes along with your distance finders:

stores=Store.find :all, :origin=>home, :include=>[:reviews,:cities] :within=>5, :order=>'distance'

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_distance_from(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=Bounds.from_point_and_radius(home,5)
stores=Store.find :all, :include=>[:reviews,:cities] :bounds=>bounds
stores.sort_by_distance_from(home)

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.

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.find_farthest(:origin => '217.15.10.9')
Location.find_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. Currently, Geokit supports Google, Yahoo, and Geocoder.us geocoding services.

These geocoder services are made available through three classes: GoogleGeocoder, YahooGeocoder, and UsGeocoder. 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 naming 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 are 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 the PROVIDER_ORDER constant 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

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 equivilent to:

class Store << ActiveRecord::Base
  acts_as_mappable
  before_validation_on_create :geocode_address

  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
midpoing=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:

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

  3. 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 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:

    PROVIDER_ORDER=[:google]

  3. 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)
    
  4. 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 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.find :all
stores.sort_by_distance_from(home)
puts stores.first.distance

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

Database Compatability

  • Geokit works with MySQL (tested with version 5.0.41) or PostgreSQL (tested with version 8.2.6)
  • Geokit does not work with SQLite, as it lacks the necessary geometry functions.
  • 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 ojbects 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 modeule goodness for free.

IMPORTANT NOTE: 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.

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