<?php
function distance($lat1, $lon1, $lat2, $lon2, $unit) {

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