Question

Here my code I used below code to calculate the distance between two location using their latitude and longitude. It is giving wrong distance. sometimes getting right and sometimes getting irrelevant distance.

We are getting lat1 and lng1 from database.

//getting lat2 and lng2 from GPS as below

public class MyLocationListener implements LocationListener {

  @Override
  public void onLocationChanged(Location loc)
  {
    lat2=loc.getLatitude();
    lng2=loc.getLongitude();
    String Text = "My current location is: " +"Latitud = "+ loc.getLatitude() +"Longitud = " + loc.getLongitude();

    //System.out.println("Lat & Lang form Loc"+Text);
    //Toast.makeText( getApplicationContext(), Text,Toast.LENGTH_SHORT).show();
  }

  @Override
  public void onProviderDisabled(String provider)
  {
  }

  @Override
  public void onProviderEnabled(String provider)
  {
  }

  @Override
  public void onStatusChanged(String provider, int status, Bundle extras)
  {
  }


  //Calculating distance
  double earthRadius = 3958.75;

  double dLat = Math.toRadians(lat1-lat2);
  double dLng = Math.toRadians(lng1-lng2);
  double a = Math.sin(dLat/2) * Math.sin(dLat/2) +
             Math.cos(Math.toRadians(lat2)) * Math.cos(Math.toRadians(lat1)) *
             Math.sin(dLng/2) * Math.sin(dLng/2);
  double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
  double dist = earthRadius * c;

Answer 1

As shown in the article at https://dzone.com/articles/distance-calculation-using-3 and in the answer at Calculating distance between two points, using latitude longitude? —

private double distance(double lat1, double lon1, double lat2, double
lon2) {
    double theta = lon1 - lon2;
    double dist = Math.sin(deg2rad(lat1)) 
                    * Math.sin(deg2rad(lat2))
                    + Math.cos(deg2rad(lat1))
                    * Math.cos(deg2rad(lat2))
                    * Math.cos(deg2rad(theta));
    dist = Math.acos(dist);
    dist = rad2deg(dist);
    dist = dist * 60 * 1.1515;
    return (dist); }

private double deg2rad(double deg) {
    return (deg * Math.PI / 180.0); }

private double rad2deg(double rad) {
    return (rad * 180.0 / Math.PI); }