Calculate distance between two latitude-longitude points?

Question

I need to calculate distance between two GPS points. I found this function in earlier post:

function getDistanceFromLatLonInKm(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;
}

I tried it, and it does not make sense. Let's say I did not move, thus lat1 and lat2 are the same. So, dLat and dLon would both be 0. Thus, term a would be 0. Term c = 2 * Math.atan2(0,1) = 3.141593 (I used Excel to get this number), and the distance d = 20015.08 km.

I am calculating distance of a vehicle moving every second given two GPS points. I am expecting small number. What is wrong here?

Answer 1

I used this code - it worked fine.

    public static double distance(MyLocation p1, MyLocation p2) {
    double theta = p1.mLongitude - p2.mLongitude;
    String unit = "K";
    double dist = Math.sin(deg2rad(p1.mLatitude)) * Math.sin(deg2rad(p2.mLatitude))
            + Math.cos(deg2rad(p1.mLatitude)) * Math.cos(deg2rad(p2.mLatitude)) * Math.cos(deg2rad(theta));
    dist = Math.acos(dist);
    dist = rad2deg(dist);
    dist = dist * 60 * 1.1515;
    if (unit == "K") {
        dist = dist * 1.609344;



    } else if (unit == "N") {
        dist = dist * 0.8684;
    }

    return (dist);
}

it calculates distances in kilometers.