diff --git a/lib/geocoder/calculations.rb b/lib/geocoder/calculations.rb
index 0152cbe0e118f350c50475e5b9df3bc95d1e54f7..f4dd7a42b232baed02af3f064e3d0d340d2ed6e4 100644
--- a/lib/geocoder/calculations.rb
+++ b/lib/geocoder/calculations.rb
@@ -48,23 +48,41 @@ module Geocoder
# Calculate bearing between two sets of coordinates.
# Returns a number of degrees from due north (clockwise).
#
+ # Also accepts an options hash:
+ #
+ # * <tt>:method</tt> - <tt>:linear</tt> (default) or <tt>:spherical</tt>;
+ # the spherical method is "correct" in that it returns the shortest path
+ # (one along a great circle) but the linear method is the default as it
+ # is less confusing (returns due east or west when given two points with
+ # the same latitude)
+ #
# Based on: http://www.movable-type.co.uk/scripts/latlong.html
#
- def bearing_between(lat1, lon1, lat2, lon2)
+ def bearing_between(lat1, lon1, lat2, lon2, options = {})
+ options[:method] = :linear unless options[:method] == :spherical
# convert degrees to radians
lat1, lon1, lat2, lon2 = to_radians(lat1, lon1, lat2, lon2)
- # compute delta
+ # compute deltas
+ dlat = lat2 - lat1
dlon = lon2 - lon1
- y = Math.sin(dlon) * Math.cos(lat2)
- x = Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) *
- Math.cos(lat2) * Math.cos(dlon)
- brng = Math.atan2(x,y)
- # brng is in radians counterclockwise from due east.
+ case options[:method]
+ when :linear
+ y = dlon
+ x = dlat
+
+ when :spherical
+ y = Math.sin(dlon) * Math.cos(lat2)
+ x = Math.cos(lat1) * Math.sin(lat2) -
+ Math.sin(lat1) * Math.cos(lat2) * 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(brng) + 360) % 360
+ (90 - to_degrees(bearing) + 360) % 360
end
##
diff --git a/lib/geocoder/orms/active_record.rb b/lib/geocoder/orms/active_record.rb
index 1194f8dca9b9187f83fc1737d89278e7e00efea5..5123618f4d914cd7133783e155426ad6457e95e2 100644
--- a/lib/geocoder/orms/active_record.rb
+++ b/lib/geocoder/orms/active_record.rb
@@ -27,9 +27,11 @@ module Geocoder::Orm
"OR #{geocoder_options[:longitude]} IS NULL"}}
##
- # Find all objects within a radius (in miles) of the given location
- # (address string). Location (the first argument) may be either a string
- # to geocode or an array of coordinates (<tt>[lat,long]</tt>).
+ # Find all objects within a radius of the given location.
+ # Location may be either a string to geocode or an array of
+ # coordinates (<tt>[lat,lon]</tt>). Also takes an options hash
+ # (see Geocoder::Orm::ActiveRecord::ClassMethods.near_scope_options
+ # for details).
#
scope :near, lambda{ |location, *args|
latitude, longitude = location.is_a?(Array) ?
@@ -56,6 +58,10 @@ module Geocoder::Orm
# * +:units+ - <tt>:mi</tt> (default) or <tt>:km</tt>; to be used
# for interpreting radius as well as the +distance+ attribute which
# is added to each found nearby object
+ # * +:bearing+ - <tt>:linear</tt> (default) or <tt>:spherical</tt>;
+ # the method to be used for calculating the bearing (direction)
+ # between the given point and each found nearby point;
+ # set to false for no bearing calculation
# * +:select+ - string with the SELECT SQL fragment (e.g. “id, nameâ€)
# * +:order+ - column(s) for ORDER BY SQL clause
# * +:limit+ - number of records to return (for LIMIT SQL clause)
@@ -76,7 +82,8 @@ module Geocoder::Orm
##
# Scope options hash for use with a database that supports POWER(),
- # SQRT(), PI(), and trigonometric functions (SIN(), COS(), and ASIN()).
+ # SQRT(), PI(), and trigonometric functions SIN(), COS(), ASIN(),
+ # ATAN2(), DEGREES(), and RADIANS().
#
# Distance calculations based on the excellent tutorial at:
# http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL
@@ -87,15 +94,28 @@ module Geocoder::Orm
def full_near_scope_options(latitude, longitude, radius, options)
lat_attr = geocoder_options[:latitude]
lon_attr = geocoder_options[:longitude]
- bearing = "(DEGREES(ATAN2( " +
- "SIN(RADIANS(#{lon_attr} - #{longitude})) * " +
- "COS(RADIANS(#{lat_attr})), (" +
- "COS(RADIANS(#{latitude})) * SIN(RADIANS(#{lat_attr}))" +
- ") - (" +
- "SIN(RADIANS(#{latitude})) * COS(RADIANS(#{lat_attr})) * " +
- "COS(RADIANS(#{lon_attr} - #{longitude}))" +
- "))) + 360)"
- bearing = "CAST(#{bearing} AS decimal) % 360"
+ options[:bearing] = :linear unless options.include?(:bearing)
+ bearing = case options[:bearing]
+ when :linear
+ "CAST(" +
+ "DEGREES(ATAN2( " +
+ "RADIANS(#{lon_attr} - #{longitude}), " +
+ "RADIANS(#{lat_attr} - #{latitude})" +
+ ")) + 360 " +
+ "AS decimal) % 360"
+ when :spherical
+ "CAST(" +
+ "DEGREES(ATAN2( " +
+ "SIN(RADIANS(#{lon_attr} - #{longitude})) * " +
+ "COS(RADIANS(#{lat_attr})), (" +
+ "COS(RADIANS(#{latitude})) * SIN(RADIANS(#{lat_attr}))" +
+ ") - (" +
+ "SIN(RADIANS(#{latitude})) * COS(RADIANS(#{lat_attr})) * " +
+ "COS(RADIANS(#{lon_attr} - #{longitude}))" +
+ ")" +
+ ")) + 360 " +
+ "AS decimal) % 360"
+ end
distance = "#{Geocoder::Calculations.earth_radius} * 2 * ASIN(SQRT(" +
"POWER(SIN((#{latitude} - #{lat_attr}) * PI() / 180 / 2), 2) + " +
"COS(#{latitude} * PI() / 180) * COS(#{lat_attr} * PI() / 180) * " +
@@ -103,7 +123,8 @@ module Geocoder::Orm
options[:order] ||= "#{distance} ASC"
default_near_scope_options(latitude, longitude, radius, options).merge(
:select => "#{options[:select] || '*'}, " +
- "#{distance} AS distance, #{bearing} AS bearing",
+ "#{distance} AS distance" +
+ (bearing ? ", #{bearing} AS bearing" : ""),
:having => "#{distance} <= #{radius}"
)
end
diff --git a/test/geocoder_test.rb b/test/geocoder_test.rb
index d0f53bbfb9fcebaa598d14b3341c4892aa33a652..fe6eae6d3789f9661d7447d5f4226b3cb98f3d1a 100644
--- a/test/geocoder_test.rb
+++ b/test/geocoder_test.rb
@@ -199,17 +199,17 @@ class GeocoderTest < Test::Unit::TestCase
:w => [40, -76]
}
directions = [:n, :e, :s, :w]
- types = [:spherical]
+ methods = [:linear, :spherical]
- types.each do |t|
+ methods.each do |m|
directions.each_with_index do |d,i|
opp = directions[(i + 2) % 4] # opposite direction
p1 = points[d]
p2 = points[opp]
- b = Geocoder::Calculations.bearing_between(*(p1 + p2))
+ b = Geocoder::Calculations.bearing_between(*(p1 + p2), :method => m)
assert (b - bearings[opp]).abs < 1,
- "Bearing (#{t}) should be close to #{bearings[opp]} but was #{b}."
+ "Bearing (#{m}) should be close to #{bearings[opp]} but was #{b}."
end
end
end