function getDistance($longitude1, $latitude1, $longitude2, $latitude2, $unit=2, $decimal=2){
$EARTH_RADIUS = 6370.996;
$PI = 3.1415926;
$radLat1 = $latitude1 * $PI / 180.0;
$radLat2 = $latitude2 * $PI / 180.0;
$radLng1 = $longitude1 * $PI / 180.0;
$radLng2 = $longitude2 * $PI /180.0;
$a = $radLat1 - $radLat2;
$b = $radLng1 - $radLng2;
$distance = 2 * asin(sqrt(pow(sin($a/2),2) + cos($radLat1) * cos($radLat2) * pow(sin($b/2),2)));
$distance = $distance * $EARTH_RADIUS * 1000;
if($unit==2){
$distance = $distance / 1000;
}
return round($distance, $decimal);
}