README.md

----------------

### The Near Method

Mongo document classes (Mongoid and MongoMapper) have a built-in `near` scope, but since it only works two-dimensions Geocoder overrides it with its own spherical `near` method in geocoded classes.

### Latitude/Longitude Order

Coordinates are generally printed and spoken as latitude, then longitude ([lat,lon]). Geocoder respects this convention and always expects method arguments to be given in [lat,lon] order. However, MongoDB requires that coordinates be stored in [lon,lat] order as per the GeoJSON spec (http://geojson.org/geojson-spec.html#positions), so internally they are stored "backwards." However, this does not affect order of arguments to methods when using Mongoid or MongoMapper.

To access an object's coordinates in the conventional order, use the `to_coordinates` instance method provided by Geocoder. For example:

    obj.to_coordinates  # => [37.7941013, -122.3951096] # [lat, lon]

Calling `obj.coordinates` directly returns the internal representation of the coordinates which, in the case of MongoDB, is probably the reverse of what you want:

    obj.coordinates     # => [-122.3951096, 37.7941013] # [lon, lat]

For consistency with the rest of Geocoder, always use the `to_coordinates` method instead.

Notes on Non-Rails Frameworks
-----------------------------

If you are using Geocoder with ActiveRecord and a framework other than Rails (like Sinatra or Padrino) you will need to add this in your model before calling Geocoder methods:

    extend Geocoder::Model::ActiveRecord

Optimisation of Distance Queries
--------------------------------

In MySQL and Postgres the finding of objects near a given point is speeded up by using a bounding box to limit the number of points over which a full distance calculation needs to be done.

To take advantage of this optimisation you need to add a composite index on latitude and longitude. In your Rails migration:

    add_index :table, [:latitude, :longitude]


Distance Queries in SQLite
--------------------------

SQLite's lack of trigonometric functions requires an alternate implementation of the `near` scope. When using SQLite, Geocoder will automatically use a less accurate algorithm for finding objects near a given point. Results of this algorithm should not be trusted too much as it will return objects that are outside the given radius, along with inaccurate distance and bearing calculations.


### Discussion

There are few options for finding objects near a given point in SQLite without installing extensions:

1. Use a square instead of a circle for finding nearby points. For example, if you want to find points near 40.71, 100.23, search for objects with latitude between 39.71 and 41.71 and longitude between 99.23 and 101.23. One degree of latitude or longitude is at most 69 miles so divide your radius (in miles) by 69.0 to get the amount to add and subtract from your center coordinates to get the upper and lower bounds. The results will not be very accurate (you'll get points outside the desired radius), but you will get all the points within the required radius.

2. Load all objects into memory and compute distances between them using the `Geocoder::Calculations.distance_between` method. This will produce accurate results but will be very slow (and use a lot of memory) if you have a lot of objects in your database.

3. If you have a large number of objects (so you can't use approach #2) and you need accurate results (better than approach #1 will give), you can use a combination of the two. Get all the objects within a square around your center point, and then eliminate the ones that are too far away using `Geocoder::Calculations.distance_between`.

Because Geocoder needs to provide this functionality as a scope, we must go with option #1, but feel free to implement #2 or #3 if you need more accuracy.


Tests
-----

Geocoder comes with a test suite (just run `rake test`) that mocks ActiveRecord and is focused on testing the aspects of Geocoder that do not involve executing database queries. Geocoder uses many database engine-specific queries which must be tested against all supported databases (SQLite, MySQL, etc). Ideally this involves creating a full, working Rails application, and that seems beyond the scope of the included test suite. As such, I have created a separate repository which includes a full-blown Rails application and some utilities for easily running tests against multiple environments:

http://github.com/alexreisner/geocoder_test


Error Handling
--------------

By default Geocoder will rescue any exceptions raised by calls to a geocoding service and return an empty array. You can override this on a per-exception basis, and also have Geocoder raise its own exceptions for certain events (eg: API quota exceeded) by using the `:always_raise` option:

    Geocoder.configure(:always_raise => [SocketError, Timeout::Error])

You can also do this to raise all exceptions:

    Geocoder.configure(:always_raise => :all)

The raise-able exceptions are:

    SocketError
    Timeout::Error
    Geocoder::OverQueryLimitError
    Geocoder::RequestDenied
    Geocoder::InvalidRequest
    Geocoder::InvalidApiKey
    Geocoder::ServiceUnavailable

Note that only a few of the above exceptions are raised by any given lookup, so there's no guarantee if you configure Geocoder to raise `ServiceUnavailable` that it will actually be raised under those conditions (because most APIs don't return 503 when they should; you may get a `Timeout::Error` instead). Please see the source code for your particular lookup for details.


Troubleshooting
---------------

### Mongoid

If you get one of these errors:

    uninitialized constant Geocoder::Model::Mongoid
    uninitialized constant Geocoder::Model::Mongoid::Mongo

you should check your Gemfile to make sure the Mongoid gem is listed _before_ Geocoder. If Mongoid isn't loaded when Geocoder is initialized, Geocoder will not load support for Mongoid.

### ActiveRecord

A lot of debugging time can be saved by understanding how Geocoder works with ActiveRecord. When you use the `near` scope or the `nearbys` method of a geocoded object, Geocoder creates an ActiveModel::Relation object which adds some attributes (eg: distance, bearing) to the SELECT clause. It also adds a condition to the WHERE clause to check that distance is within the given radius. Because the SELECT clause is modified, anything else that modifies the SELECT clause may produce strange results, for example:

* using the `pluck` method (selects only a single column)
* specifying another model through `includes` (selects columns from other tables)

### Unexpected Responses from Geocoding Services

Take a look at the server's raw response. You can do this by getting the request URL in an app console:

    Geocoder::Lookup.get(:google).query_url(Geocoder::Query.new("..."))

Replace `:google` with the lookup you are using and replace `...` with the address you are trying to geocode. Then visit the returned URL in your web browser. Often the API will return an error message that helps you resolve the problem. If, after reading the raw response, you believe there is a problem with Geocoder, please post an issue and include both the URL and raw response body.

You can also fetch the response in the console:

    Geocoder::Lookup.get(:google).send(:fetch_raw_data, Geocoder::Query.new("..."))


Reporting Issues
----------------

When reporting an issue, please list the version of Geocoder you are using and any relevant information about your application (Rails version, database type and version, etc). Also avoid vague language like "it doesn't work." Please describe as specifically as you can what behavior your are actually seeing (eg: an error message? a nil return value?).

Please DO NOT use GitHub issues to ask questions about how to use Geocoder. Sites like [StackOverflow](http://www.stackoverflow.com/) are a better forum for such discussions.


### Known Issue

You cannot use the `near` scope with another scope that provides an `includes` option because the `SELECT` clause generated by `near` will overwrite it (or vice versa).

Instead of using `includes` to reduce the number of database queries, try using `joins` with either the `:select` option or a call to `preload`. For example:

    # Pass a :select option to the near scope to get the columns you want.
    # Instead of City.near(...).includes(:venues), try:
    City.near("Omaha, NE", 20, :select => "cities.*, venues.*").joins(:venues)

    # This preload call will normally trigger two queries regardless of the
    # number of results; one query on hotels, and one query on administrators.
    # Instead of Hotel.near(...).includes(:administrator), try:
    Hotel.near("London, UK", 50).joins(:administrator).preload(:administrator)

If anyone has a more elegant solution to this problem I am very interested in seeing it.


Contributing
------------

Contributions are welcome via Github pull requests. If you are new to the project and looking for a way to get involved, try picking up an issue with a "beginner-task" label. Hints about what needs to be done are usually provided.

For all contributions, please respect the following guidelines:

* Each pull request should implement ONE feature or bugfix. If you want to add or fix more than one thing, submit more than one pull request.
* Do not commit changes to files that are irrelevant to your feature or bugfix (eg: `.gitignore`).
* Do not add dependencies on other gems.
* Do not add unnecessary `require` statements which could cause LoadErrors on certain systems.
* Remember: Geocoder needs to run outside of Rails. Don't assume things like ActiveSupport are available.
* Be willing to accept criticism and work on improving your code; Geocoder is used by thousands of developers and care must be taken not to introduce bugs.
* Be aware that the pull request review process is not immediate, and is generally proportional to the size of the pull request.
* If your pull request is merged, please do not ask for an immediate release of the gem. There are many factors contributing to when releases occur (remember that they affect thousands of apps with Geocoder in their Gemfiles). If necessary, please install from the Github source until the next official release.


Copyright (c) 2009-15 Alex Reisner, released under the MIT license