Distance between two addresses using google maps and the Haversine forumla

harvesine.rb

require 'open-uri'
require "rexml/document"

# 
# 
# Distance between two addresses using google maps and the Haversine forumla
# (http://en.wikipedia.org/wiki/Haversine_formula) based on the JS implementation
# (http://www.movable-type.co.uk/scripts/latlong.html)
# 
# 

GM_APIKEY = "ABQIAAAAuunGS_VtjHf9ymsKEjhoRBT2yXp_ZAY8_ufC3CFXhHIE1NvwkxQiRG09L8LvCecfieIFyIMNkGEZxg"

def get_distance(address1, address2)
  pointA = get_coordinates(address1)
  pointB = get_coordinates(address2)
  
  # Haversine rules :)
  earth_radius = 6371 # km
  dLat = ((Float(pointA[0])-Float(pointB[0]))*Math::PI)/180
  dLon = ((Float(pointA[1])-Float(pointB[1]))*Math::PI)/180
  a = Math.sin(dLat/2) * Math.sin(dLat/2) +
      Math.cos((Float(pointA[0])*Math::PI)/180) * Math.cos((Float(pointB[0])*Math::PI)/180) * 
      Math.sin(dLon/2) * Math.sin(dLon/2)
  c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))
  d = earth_radius * c
end

def get_coordinates(address)
  doc = REXML::Document.new(open("http://maps.google.com/maps/geo?q=#{address.gsub(" ", "+")}&output=xml&key=#{GM_APIKEY}"))
  doc.elements.to_a("//coordinates").first.text.split(",")
end


# using postal code and country code
get_distance("03400 ES", "28002 ES")