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# haversine.rb
#
# haversine formula to compute the great circle distance between two points given their latitude and longitudes
#
# Copyright (C) 2008, 360VL, Inc
# Copyright (C) 2008, Landon Cox
#
# http://www.esawdust.com (Landon Cox)
# contact:
# http://www.esawdust.com/blog/businesscard/businesscard.html
#
# LICENSE: GNU Affero GPL v3
# The ruby implementation of the Haversine formula is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License version 3 as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
# License version 3 for more details. http://www.gnu.org/licenses/
#
# Landon Cox - 9/25/08
#
# Notes:
#
# translated into Ruby based on information contained in:
# http://mathforum.org/library/drmath/view/51879.html Doctors Rick and Peterson - 4/20/99
# http://www.movable-type.co.uk/scripts/latlong.html
# http://en.wikipedia.org/wiki/Haversine_formula
#
# This formula can compute accurate distances between two points given latitude and longitude, even for
# short distances.
# PI = 3.1415926535
RAD_PER_DEG = 0.017453293 # PI/180
# the great circle distance d will be in whatever units R is in
Rmiles = 3956 # radius of the great circle in miles
Rkm = 6371 # radius in kilometers...some algorithms use 6367
Rfeet = Rmiles * 5282 # radius in feet
Rmeters = Rkm * 1000 # radius in meters
=begin rdoc
given two lat/lon points, compute the distance between the two points using the haversine formula
the result will be a Hash of distances which are key'd by 'mi','km','ft', and 'm'
=end
module Foursquare
class Checkin
def distance_from(checkin2)
lon1 = self.venue.location.lng
lat1 = self.venue.location.lat
lon2 = checkin2.venue.location["lat"]
lat2 = checkin2.venue.location["lng"]
dlon = lon2 - lon1
dlat = lat2 - lat1
dlon_rad = dlon * RAD_PER_DEG
dlat_rad = dlat * RAD_PER_DEG
lat1_rad = lat1 * RAD_PER_DEG
lon1_rad = lon1 * RAD_PER_DEG
lat2_rad = lat2 * RAD_PER_DEG
lon2_rad = lon2 * RAD_PER_DEG
# puts "dlon: #{dlon}, dlon_rad: #{dlon_rad}, dlat: #{dlat}, dlat_rad: #{dlat_rad}"
a = (Math.sin(dlat_rad/2))**2 + Math.cos(lat1_rad) * Math.cos(lat2_rad) * (Math.sin(dlon_rad/2))**2
c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a))
return Rkm * c # delta in kilometers
end
end
end