code: public static double distance(double lat1, double lon1,
                                  double lat2, double lon2) {
      double dLat = Math.toRadians(lat2-lat1);
      double dLon = Math.toRadians(lon2-lon1);
      lat1 = Math.toRadians(lat1);
      lat2 = Math.toRadians(lat2);
  
      double a = Math.sin(dLat/2) * Math.sin(dLat/2) +
          Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
      double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
      return R * c;
    }
docs: Returns the distance between the two points in meters.