PHP distance by latitude and longitude of two locations

<?php
/**
* Find the distance between two known longitude and latitude, in meters
* @param lng1,lng2 Longitude
* @param LAT1,LAT2 Latitude
* @return float distance, Unit meter
* @author Yalong Sun<[email protected]>
**/
function Getdistance ($lng 1, $lat 1, $lng 2, $lat 2) {
Turn angle into Fox degree
$radLat 1=deg2rad ($lat 1);//deg2rad () function converts an angle to radians
$radLat 2=deg2rad ($lat 2);
$radLng 1=deg2rad ($lng 1);
$radLng 2=deg2rad ($lng 2);
$a = $radLat 1-$radLat 2;
$b = $radLng 1-$radLng 2;
$s =2*asin (sqrt (Pow (sin ($a/2), 2) +cos ($radLat 1) *cos ($radLat 2) *pow (sin ($b/2), 2)) *6378.137*1000;
return $s;
}
echo getdistance (116.46865,39.914638,116.482233,39.91425);
?>

PHP distance by latitude and longitude of two locations