Distance calculate

    private function distance($currentCity, $city, $unit = 'M')
    {
        $lat1 = $currentCity->latitude;
        $lon1 = $currentCity->longitude;
        $lat2 = $city->latitude;
        $lon2 = $city->longitude;
        if ($lat1 == $lat2 && $lon1 == $lon2) {
            return 0;
        }
        $theta  = $lon1 - $lon2;
        $dist   =
            sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +
            cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
        $dist   = acos($dist);
        $dist   = rad2deg($dist);
        $miles  = $dist * 60 * 1.1515;
        $unit   = strtoupper($unit);


        if ($unit == "K") {
            return ($miles * 1.609344);
        } elseif ($unit == "N") {
            return ($miles * 0.8684);
        } else {
            return $miles;
        }
    }