Calculate the distance between two points on Earth

geo.rb

module Geo
  def self.distance(point_a = {}, point_b = {})
    # http://en.wikipedia.org/wiki/Haversine_formula

    r = 6371.009  # IUGG mean radius of the Earth

    deg2rad = lambda { |d| d * Math::PI / 180 }
    sin2 = lambda { |x| Math.sin(x) ** 2 }

    lat1 = deg2rad.call(point_a['lat'])
    lat2 = deg2rad.call(point_b['lat'])

    dlat = lat2 - lat1
    dlng = deg2rad.call(point_b['lng']) - deg2rad.call(point_a['lng'])

    r * 2 *
      Math.asin(
        Math.sqrt(
          sin2.call(dlat / 2) + Math.cos(lat1) *
          Math.cos(lat2) * sin2.call(dlng / 2)
        )
      )
  end
end