php根据两点经纬度计算距离

<?php
$lng1 = 117.11596;
$lat1 = 36.701615;
$lng2 = 117.134968;
$lat2 = 36.692355;

$EARTH_RADIUS = 6378137;   //地球半径
$RAD          = pi() / 180.0;

$radLat1 = $lat1 * $RAD;
$radLat2 = $lat2 * $RAD;

$latDif = $radLat1 - $radLat2;//纬度差
$lngDif = ($lng1 - $lng2) * $RAD;//经度差

$s = 2 * asin(sqrt(pow(sin($latDif / 2), 2) + cos($radLat1) * cos($radLat2) * pow(sin($lngDif / 2), 2)));
$s = $s * $EARTH_RADIUS;
$s = round($s * 10000) / 10000;

$distance_str = sprintf('%.2f',($s/1000)).'km';
echo $distance_str;