distanceInKilometers2 function
Implementation
double distanceInKilometers2(GeoPoint p1, GeoPoint p2) {
final earthRadius = 6378.137; // WGS84 major axis
final lon1 = degreesToRadians(p1.longitude);
final lon2 = degreesToRadians(p2.longitude);
final lat1 = degreesToRadians(p1.latitude);
final lat2 = degreesToRadians(p2.latitude);
final distance = acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos(lon2 - lon1));
return distance * earthRadius;
}