code: public static function gpsDistance($lat1, $lon1, $lat2, $lon2)
      {
          $lat1 = deg2rad($lat1);
          $lon1 = deg2rad($lon1);
          $lat2 = deg2rad($lat2);
          $lon2 = deg2rad($lon2);
  
          $lonDelta = $lon2 - $lon1;
          $a = ((cos($lat2) * sin($lonDelta)) ** 2) + ((cos($lat1) * sin($lat2) - sin($lat1) * cos($lat2) * cos($lonDelta)) ** 2);
          $b = sin($lat1) * sin($lat2) + cos($lat1) * cos($lat2) * cos($lonDelta);
  
          return atan2(sqrt($a), $b) * 6371.0088;
      }
docs: Calculates distance in kilometers between two GPS coordinates
  
  @param float $lat1 GPS latitude 1
  @param float $lon1 GPS longitude 1
  @param float $lat2 GPS latitude 2
  @param float $lon2 GPS longitude 2
  
  @return float Distance between points in kilometers
  @static