function getGeoDistance($lat1, $lon1, $lat2, $lon2) {
  $earthRadius = 6371000;
  $lat1 = deg2rad($lat1);
  $lon1 = deg2rad($lon1);
  $lat2 = deg2rad($lat2);
  $lon2 = deg2rad($lon2);

  $dLat = $lat2 - $lat1;
  $dLon = $lon2 - $lon1;

  $a = sin($dLat/2) * sin($dLat/2) + cos($lat1) * cos($lat2) * sin($dLon/2) * sin($dLon/2);
  $c = 2 * atan2(sqrt($a), sqrt(1-$a));

  $distance = $earthRadius * $c;

  return ($distance);
}