function haversine_distance(mk1, mk2) {
      var R = 3958.8; // Radius of the Earth in miles
      var rlat1 = mk1.position.lat() * (Math.PI/180); // Convert degrees to radians
      var rlat2 = mk2.position.lat() * (Math.PI/180); // Convert degrees to radians
      var difflat = rlat2-rlat1; // Radian difference (latitudes)
      var difflon = (mk2.position.lng()-mk1.position.lng()) * (Math.PI/180); // Radian difference (longitudes)

      var d = 2 * R * Math.asin(Math.sqrt(Math.sin(difflat/2)*Math.sin(difflat/2)+Math.cos(rlat1)*Math.cos(rlat2)*Math.sin(difflon/2)*Math.sin(difflon/2)));
      return d;
    }