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Geo-spatial extension for Mongoid 2

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README.textile

Mongoid geo

A Geo extension for Mongoid.

MongoDB Geospatial Indexing

  • Supports Mongo DB 1.7+ sphere distance calculations
  • Adds nearSphere inclusion method
  • Adds a set of geo related inflections
  • Adds an exta option for defining a “geo” field, to have the generated attr_writer parse and convert strings etc. to float arrays.
  • Calculate locations near a given point (geoNear)

Mongoid 2 geo features

The following summarized what geo functionality is already provided by Mongoid 2.0 (as far as I could tell, May 9th, 2011)

Find addresses near a point

  Address.near(:latlng => [37.761523, -122.423575, 1])

Find locations within a circle

  base.where(:location.within => { "$center" => [ [ 50, -40 ], 1 ] })

Create geo-spatial index

  class Person
    field :location, :type => Array
    index [[ :location, Mongo::GEO2D ]], :min => -180, :max => 180
  end

  # to ensure indexes are created, either:
  Mongoid.autocreate_indexes = true

  # or in the mongoid.yml
  autocreate_indexes: true

These are the only geo features I could find that are currently built-in for Mongoid 2.

Mongoid Geo implements some nice extra geo features:

Mongoid Geo features

The following briefly demonstrates all the features that mongoid-geo provides:

Geo index

A new geo_index class method

Usage example:

geo_index :location

Note: For embedded documents, you must define the index in the root collection class. (davemitchell)

Geo option for Array GPS location field

Objective: When setting a geo GPS location array, the setter should try to convert the value to an array of floats

The “old” manual way:

  class Person
    field :locations, :type => Array

    def locations= args
      @locations = args.kind_of?(String) ? args.split(",").map(&:to_f) : args
    end
  end

mongoid-geo provides a new :geo option that can be used with any Array field:

Usage example:

  class Person
    field :location, :type => Array, :geo => true

    geo_index :location
  end

   p = Person.new

   # A Geo array can now be set via String or Strings, Hash or Object, here a few examples...
   # Please see geo_fields_spec.rb for more options!

   p.location = "45.1, -3.4"
   p.location = "45.1", "-3.4"
   p.location = {:lat => 45.1, :lng => -3.4}
   p.location = [{:lat => 45.1, :lng => -3.4}]
   p.location = {:latitude => 45.1, :longitude => -3.4}

   my_location  = Location.new :latitude => 45.1, :longitude => -3.4
   p.location   = my_location

   # for each of the above, the following holds
   assert([45.1, -3.4], p.location)

   # also by default adds #lat and #lng convenience methods (thanks to TeuF)

   assert(45.1 , p.lat)
   assert(-3.4 , p.lng)

   # the #lat and #lng convenience methods can also be customized with the :lat and :lng options
  field :location, :type => Array, :geo => true, :lat => :latitude, :lng => :longitude

  assert(45.1 , p.latitude)
  assert(-3.4 , p.longitude)

  # or set the array attributes using symmetric setter convenience methods!
  p.latitude   = 44
  assert(44 , p.latitude)

  # You can also reverse the lat/lng positioning of the array storage - this is fx useful for spherical calculations
  
  Mongoid::Geo.spherical_mode do
    # Mongoid::Geo.lat_index.should == 1
    # Mongoid::Geo.lng_index.should == 0
    address.location = "23.5, -47"
    address.location.should == [23.5, -47].reverse
  end  

  # or alternatively 
  Mongoid::Geo.spherical = true
  
  address.location = "23.5, -47"
  address.location.should == [23.5, -47].reverse  

geoNear

class Address
  include Mongoid::Document
  extend Mongoid::Geo::Near

  field :location, :type => Array, :geo => true
  ...
end

# Find all addresses sorted nearest to a specific address loation
nearest_addresses = Address.geoNear(another_address, :location)

class Position
  include Mongoid::Document

  field :pos, :type => Array, :geo => true
  ...
end

Find all positions sorted nearest to the address loation

nearest_positions = Position.geoNear(another_address.location, :pos)

Perform distance locations in Speherical mode inside Mongo DB (default is :plane)

nearest_positions = Position.geoNear(another_address.location, :pos, :mode => :sphere)

Other options supported are: :num, :maxDistance, :distanceMultiplier, :query

GeoNear returns each distance calculated in degrees. Use the :distanceMultiplier or :unit option to return in the unit of your choice (see unit.rb).

Set :distanceMultiplier = 6371 to get distance in KMs
Set @:distanceMultiplier = @3963.19 to get distance in Miles

You can also use the :unit option instead like this (supports :feet, :meters, :kms, :miles):

results = Address.geoNear @center.location, :location, :unit => :feet, :dist_order => :desc

The geoNear query result is returned as a Mongoid::Criteria

results.desc(:distance).map(&:distance)

Note that the :fromLocation field, stores the location the distance was last calculated as a Hash of the GPS location point it was calculated from:

[23.5, -47].hash

This hash can be retrieved (and used for comparison?) using the fromHash field

from = results.first.fromHash

You can also at any time get the GPS location point which the distance of any result instance was calculated from, using the @fromPoint field

from = results.first.fromPoint

You can now explicitly set/configure the Mongo DB version used. This will affect whether built-in Mongo DB distance calculation will be used or using standalone Ruby Haversine algorithm. By default the Mongo DB version is set to 1.8 (as of May 9, 2011) . See geo_near specs for more details/info on this.

Mongoid::Geo.mongo_db_version = 1.7

Mongoid Geo extra inclusions

Find addresses near a point using spherical distance calculation

  Address.nearSphere(:location => [ 72, -44 ])

Mongoid Geo extra inflections

nearSphere

  base.where(:location.nearSphere => [ 72, -44 ])
  # => :location => { "$nearSphere" : [ 72, -44 ] }

nearMax

Find points near a given point within a maximum distance

  base.where(:location.nearMax => [[ 72, -44 ], 5])
  # => { $near: [50, 40] , $maxDistance: 3 }

  base.where(:location.nearMax(:sphere) => [[ 72, -44 ], 5])
  # => { $nearSphere: [50, 40] , $maxDistanceSphere: 3 }

  base.where(:location.nearMax(:sphere, :flat) => [[ 72, -44 ], 5])
  # => { $nearSphere: [50, 40] , $maxDistance: 3 }

You can also use a Hash to define the nearMax

  places.where(:location.nearMax => {:point => [ 72, -44 ], :distance => 5})

Or use an Object (which must have the methods #point and #distance that return the point and max distance from that point)

  near_max_ = (Struct.new :point, :distance).new
  near_max.point = [50, 40]
  near_max.distance = [30,55]

  places.where(:location.nearMax => near_max)

Note: For the points, you can also use a hash or an object with the methods/keys, either :lat, :lng or :latitude, :longitude

Example:

  center = (Struct.new :lat, :lng).new
  center.lat = 72
  center.lng = -44
  places.where(:location.withinCenter => [center, radius])

  # OR

  places.where(:location.withinCenter => [{:lat => 72, :lng => -44}, radius])

withinBox

  box = [[50, 40], [30,55]]
  base.where(:location.withinBox => box)
  # => locations: {"$within" : {"$box" : [[50, 40], [30,55]]}

  base.where(:location.withinBox(:sphere) => box)
  # => locations: {"$within" : {"$boxSphere" : [[50, 40], [30,55]]}

You can also use a Hash to define the box

  places.where(:location.withinBox => {:lower_left => [50, 40], :upper_right => [30,55]})

  # or mix and match

  places.where(:location.withinBox => {:lower_left => {:lat => 50, :lng => 40}, :upper_right => [30,55] } )

Or use an object (which must have the methods #lower_left and #upper_right that return the points of the bounding box)

  box = (Struct.new :lower_left, :upper_right).new
  box.lower_left =  [50, 40]
  box.upper_right = [30, 55]

  places.where(:location.withinBox => box)

withinCenter

  center = [50, 40]
  radius = 4

  places.where(:location.withinCenter => [center, radius])
  # => places: {"$within" : {"$center" : [[50, 40], 4]}

  places.where(:location.withinCenter(:sphere) => [center, radius])
  # => places: {"$within" : {"$centerSphere" : [[50, 40], 4]}

You can also use a hash to define the circle, with :center and :radius keys

  places.where(:location.withinCenter => {:center => [50, 40], :radius => 4})

Or use an object (which must have the methods #lower_left and #upper_right that return the points of the bounding box)

  circle = (Struct.new :center, :radius).new
  circle.center = [50, 40]
  circle.radius = 4

  places.where(:location.withinCenter => circle)
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