# Module: Geocoder::Calculations

Extended by:
Calculations
Included in:
Calculations
Defined in:
lib/geocoder/calculations.rb

## Constant Summary

COMPASS_POINTS =

Compass point names, listed clockwise starting at North.

If you want bearings named using more, fewer, or different points override Geocoder::Calculations.COMPASS_POINTS with your own array.

`%w[N NE E SE S SW W NW]`

`6371.0`
KM_IN_MI =

Conversion factor: multiply by kilometers to get miles.

`0.621371192`
KM_IN_NM =

Conversion factor: multiply by nautical miles to get miles.

`0.539957`
NAN =

Not a number constant

`defined?(::Float::NAN) ? ::Float::NAN : 0 / 0.0`

## Instance Method Summary (collapse)

• Bearing between two points on Earth.

• Returns coordinates of the southwest and northeast corners of a box with the given point at its center.

• Translate a bearing (float) into a compass direction (string, eg “North”).

• Returns true if all given arguments are valid latitude/longitude values.

• Distance between two points on Earth (Haversine formula).

• Radius of the Earth in the given units (:mi or :km).

• Takes an object which is a [lat,lon] array, a geocodable string, or an object that implements to_coordinates and returns a [lat,lon] array.

• Compute the geographic center (aka geographic midpoint, center of gravity) for an array of geocoded objects and/or [lat,lon] arrays (can be mixed).

• Conversion factor: km to mi.

• Conversion factor: km to nm.

• Distance spanned by one degree of latitude in the given units.

• Distance spanned by one degree of longitude at the given latitude.

• Conversion factor: mi to km.

• Conversion factor: nm to km.

• Convert miles to kilometers.

• Convert kilometers to miles.

• Convert kilometers to nautical miles.

## Instance Method Details

### - (Object) bearing_between(point1, point2, options = {})

Bearing between two points on Earth. Returns a number of degrees from due north (clockwise).

See Geocoder::Calculations.distance_between for ways of specifying the points. Also accepts an options hash:

• :method - :linear or :spherical; the spherical method is “correct” in that it returns the shortest path (one along a great circle) but the linear method is less confusing (returns due east or west when given two points with the same latitude). Use Geocoder.configure(:distances => …) to configure calculation method.

 ``` 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148``` ```# File 'lib/geocoder/calculations.rb', line 115 def bearing_between(point1, point2, options = {}) # set default options options[:method] ||= Geocoder.config.distances options[:method] = :linear unless options[:method] == :spherical # convert to coordinate arrays point1 = extract_coordinates(point1) point2 = extract_coordinates(point2) # convert degrees to radians point1 = to_radians(point1) point2 = to_radians(point2) # compute deltas dlat = point2[0] - point1[0] dlon = point2[1] - point1[1] case options[:method] when :linear y = dlon x = dlat when :spherical y = Math.sin(dlon) * Math.cos(point2[0]) x = Math.cos(point1[0]) * Math.sin(point2[0]) - Math.sin(point1[0]) * Math.cos(point2[0]) * Math.cos(dlon) end bearing = Math.atan2(x,y) # Answer is in radians counterclockwise from due east. # Convert to degrees clockwise from due north: (90 - to_degrees(bearing) + 360) % 360 end```

### - (Object) bounding_box(point, radius, options = {})

Returns coordinates of the southwest and northeast corners of a box with the given point at its center. The radius is the shortest distance from the center point to any side of the box (the length of each side is twice the radius).

This is useful for finding corner points of a map viewport, or for roughly limiting the possible solutions in a geo-spatial search (ActiveRecord queries use it thusly).

See Geocoder::Calculations.distance_between for ways of specifying the point. Also accepts an options hash:

• :units - :mi or :km. Use Geocoder.configure(:units => …) to configure default units.

 ``` 207 208 209 210 211 212 213 214 215 216 217``` ```# File 'lib/geocoder/calculations.rb', line 207 def bounding_box(point, radius, options = {}) lat,lon = extract_coordinates(point) radius = radius.to_f units = options[:units] || Geocoder.config.units [ lat - (radius / latitude_degree_distance(units)), lon - (radius / longitude_degree_distance(lat, units)), lat + (radius / latitude_degree_distance(units)), lon + (radius / longitude_degree_distance(lat, units)) ] end```

### - (Object) compass_point(bearing, points = COMPASS_POINTS)

Translate a bearing (float) into a compass direction (string, eg “North”).

 ``` 153 154 155 156``` ```# File 'lib/geocoder/calculations.rb', line 153 def compass_point(bearing, points = COMPASS_POINTS) seg_size = 360 / points.size points[((bearing + (seg_size / 2)) % 360) / seg_size] end```

### - (Boolean) coordinates_present?(*args)

Returns true if all given arguments are valid latitude/longitude values.

Returns:

• (Boolean)
 ``` 35 36 37 38 39 40 41 42``` ```# File 'lib/geocoder/calculations.rb', line 35 def coordinates_present?(*args) args.each do |a| # note that Float::NAN != Float::NAN # still, this could probably be improved: return false if (!a.is_a?(Numeric) or a.to_s == "NaN") end true end```

### - (Object) distance_between(point1, point2, options = {})

Distance between two points on Earth (Haversine formula). Takes two points and an options hash. The points are given in the same way that points are given to all Geocoder methods that accept points as arguments. They can be:

• an array of coordinates ([lat,lon])

• a geocoded object (one which implements a to_coordinates method which returns a [lat,lon] array

The options hash supports:

• :units - :mi or :km Use Geocoder.configure(:units => …) to configure default units.

 ``` 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98``` ```# File 'lib/geocoder/calculations.rb', line 77 def distance_between(point1, point2, options = {}) # set default options options[:units] ||= Geocoder.config.units # convert to coordinate arrays point1 = extract_coordinates(point1) point2 = extract_coordinates(point2) # convert degrees to radians point1 = to_radians(point1) point2 = to_radians(point2) # compute deltas dlat = point2[0] - point1[0] dlon = point2[1] - point1[1] a = (Math.sin(dlat / 2))**2 + Math.cos(point1[0]) * (Math.sin(dlon / 2))**2 * Math.cos(point2[0]) c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a)) c * earth_radius(options[:units]) end```

### - (Object) distance_to_radians(distance, units = nil)

 ``` 247 248 249 250``` ```# File 'lib/geocoder/calculations.rb', line 247 def distance_to_radians(distance, units = nil) units ||= Geocoder.config.units distance.to_f / earth_radius(units) end```

### - (Object) earth_radius(units = nil)

Radius of the Earth in the given units (:mi or :km). Use Geocoder.configure(:units => …) to configure default units.

 ``` 282 283 284 285 286 287 288 289``` ```# File 'lib/geocoder/calculations.rb', line 282 def earth_radius(units = nil) units ||= Geocoder.config.units case units when :km; EARTH_RADIUS when :mi; to_miles(EARTH_RADIUS) when :nm; to_nautical_miles(EARTH_RADIUS) end end```

### - (Object) extract_coordinates(point)

Takes an object which is a [lat,lon] array, a geocodable string, or an object that implements to_coordinates and returns a

lat,lon

array. Note that if a string is passed this may be a slow-

running method and may return nil.

 ``` 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348``` ```# File 'lib/geocoder/calculations.rb', line 327 def extract_coordinates(point) case point when Array if point.size == 2 lat, lon = point if !lat.nil? && lat.respond_to?(:to_f) and !lon.nil? && lon.respond_to?(:to_f) then return [ lat.to_f, lon.to_f ] end end when String point = Geocoder.coordinates(point) and return point else if point.respond_to?(:to_coordinates) if Array === array = point.to_coordinates return extract_coordinates(array) end end end [ NAN, NAN ] end```

### - (Object) geographic_center(points)

Compute the geographic center (aka geographic midpoint, center of gravity) for an array of geocoded objects and/or [lat,lon] arrays (can be mixed). Any objects missing coordinates are ignored. Follows the procedure documented at www.geomidpoint.com/calculation.html.

 ``` 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189``` ```# File 'lib/geocoder/calculations.rb', line 164 def geographic_center(points) # convert objects to [lat,lon] arrays and convert degrees to radians coords = points.map{ |p| to_radians(extract_coordinates(p)) } # convert to Cartesian coordinates x = []; y = []; z = [] coords.each do |p| x << Math.cos(p[0]) * Math.cos(p[1]) y << Math.cos(p[0]) * Math.sin(p[1]) z << Math.sin(p[0]) end # compute average coordinate values xa, ya, za = [x,y,z].map do |c| c.inject(0){ |tot,i| tot += i } / c.size.to_f end # convert back to latitude/longitude lon = Math.atan2(ya, xa) hyp = Math.sqrt(xa**2 + ya**2) lat = Math.atan2(za, hyp) # return answer in degrees to_degrees [lat, lon] end```

### - (Object) km_in_mi

Conversion factor: km to mi.

 ``` 294 295 296``` ```# File 'lib/geocoder/calculations.rb', line 294 def km_in_mi KM_IN_MI end```

### - (Object) km_in_nm

Conversion factor: km to nm.

 ``` 301 302 303``` ```# File 'lib/geocoder/calculations.rb', line 301 def km_in_nm KM_IN_NM end```

### - (Object) latitude_degree_distance(units = nil)

Distance spanned by one degree of latitude in the given units.

 ``` 47 48 49 50``` ```# File 'lib/geocoder/calculations.rb', line 47 def latitude_degree_distance(units = nil) units ||= Geocoder.config.units 2 * Math::PI * earth_radius(units) / 360 end```

### - (Object) longitude_degree_distance(latitude, units = nil)

Distance spanned by one degree of longitude at the given latitude. This ranges from around 69 miles at the equator to zero at the poles.

 ``` 56 57 58 59``` ```# File 'lib/geocoder/calculations.rb', line 56 def longitude_degree_distance(latitude, units = nil) units ||= Geocoder.config.units latitude_degree_distance(units) * Math.cos(to_radians(latitude)) end```

### - (Object) mi_in_km

Conversion factor: mi to km.

 ``` 310 311 312``` ```# File 'lib/geocoder/calculations.rb', line 310 def mi_in_km 1.0 / KM_IN_MI end```

### - (Object) nm_in_km

Conversion factor: nm to km.

 ``` 317 318 319``` ```# File 'lib/geocoder/calculations.rb', line 317 def nm_in_km 1.0 / KM_IN_NM end```

 ``` 252 253 254 255``` ```# File 'lib/geocoder/calculations.rb', line 252 def radians_to_distance(radians, units = nil) units ||= Geocoder.config.units radians * earth_radius(units) end```

### - (Object) to_degrees(*args)

Convert radians to degrees. If an array (or multiple arguments) is passed, converts each value and returns array.

 ``` 238 239 240 241 242 243 244 245``` ```# File 'lib/geocoder/calculations.rb', line 238 def to_degrees(*args) args = args.first if args.first.is_a?(Array) if args.size == 1 (args.first * 180.0) / Math::PI else args.map{ |i| to_degrees(i) } end end```

### - (Object) to_kilometers(mi)

Convert miles to kilometers.

 ``` 260 261 262``` ```# File 'lib/geocoder/calculations.rb', line 260 def to_kilometers(mi) mi * mi_in_km end```

### - (Object) to_miles(km)

Convert kilometers to miles.

 ``` 267 268 269``` ```# File 'lib/geocoder/calculations.rb', line 267 def to_miles(km) km * km_in_mi end```

### - (Object) to_nautical_miles(km)

Convert kilometers to nautical miles.

 ``` 274 275 276``` ```# File 'lib/geocoder/calculations.rb', line 274 def to_nautical_miles(km) km * km_in_nm end```

 ``` 224 225 226 227 228 229 230 231``` ```# File 'lib/geocoder/calculations.rb', line 224 def to_radians(*args) args = args.first if args.first.is_a?(Array) if args.size == 1 args.first * (Math::PI / 180) else args.map{ |i| to_radians(i) } end end```