haversine_salvador (v9)

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = deg2rad(lat2 - lat1); // deg2rad below
  var dLon = deg2rad(lon2 - lon1);
  var a =
    Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);

  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c; // Distance in km
  return d;
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371;
  var dLat = deg2rad(lat2 - lat1);
  var dLon = deg2rad(lon2 - lon1);
  var a =
    0.5 - Math.cos(dLat) / 2 +
    Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
    (1 - Math.cos(dLon)) / 2;

  return R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = (lat2 - lat1) * Math.PI / 180; // deg2rad below
  var dLon = (lon2 - lon1) * Math.PI / 180;
  var a =
    0.5 - Math.cos(dLat) / 2 +
    Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) *
    (1 - Math.cos(dLon)) / 2;

  return R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = (lat2 - lat1) * Math.PI / 180; // deg2rad below
  var dLon = (lon2 - lon1) * Math.PI / 180;
  var a =
    0.5 - Math.cos(dLat) / 2 +
    Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) *
    (1 - Math.cos(dLon)) / 2;

  return R * 2 * Math.asin(Math.sqrt(a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var deg2rad = Math.PI / 180;
  lat1 *= deg2rad;
  lon1 *= deg2rad;
  lat2 *= deg2rad;
  lon2 *= deg2rad;
  var diam = 12742; // Diameter of the earth in km (2 * 6371)
  var dLat = lat2 - lat1;
  var dLon = lon2 - lon1;
  var a = (
    (1 - Math.cos(dLat)) +
    (1 - Math.cos(dLon)) * Math.cos(lat1) * Math.cos(lat2)
  ) / 2;

  return diam * Math.asin(Math.sqrt(a));
}

distance(48, -122, 49, -121);

        public static double calculateDistance(double lat1, double lon1,
                        double lat2, double lon2) {
                // convert coordinates to radians from degrees
                lat1 = toRadians(lat1);
                lon1 = toRadians(lon1);
                lat2 = toRadians(lat2);
                lon2 = toRadians(lon2);

                // calculate
                //NOTE td_IPPT00055645 - round the distance to 2 decimal places before returning 
                return round(Math.acos(Math.cos(lat1) * Math.cos(lon1) * Math.cos(lat2)
                                * Math.cos(lon2) + Math.cos(lat1) * Math.sin(lon1)
                                * Math.cos(lat2) * Math.sin(lon2) + Math.sin(lat1)
                                * Math.sin(lat2))
                                * EARTH_RADIUS, 2);
        }

function distance(lat1, lon1, lat2, lon2) {
  var deg2rad = 0.017453292519943295; // === Math.PI / 180
  var cos = Math.cos;
  lat1 *= deg2rad;
  lon1 *= deg2rad;
  lat2 *= deg2rad;
  lon2 *= deg2rad;
  var a = (
    (1 - cos(lat2 - lat1)) +
    (1 - cos(lon2 - lon1)) * cos(lat1) * cos(lat2)
  ) / 2;

  return 12742 * Math.asin(Math.sqrt(a)); // Diameter of the earth in km (2 * 6371)
}

distance(48, -122, 49, -121);