php根据经纬度计算两点直接的距离

distanceBetween.php

<?php
/**
* 计算两个坐标之间的距离(米)
* @param float $fP1Lat 起点(纬度)
* @param float $fP1Lon 起点(经度)
* @param float $fP2Lat 终点(纬度)
* @param float $fP2Lon 终点(经度)
* @return int
*/
function distanceBetween($mylonlat, $findlonlat){
        $mylonlat = explode(',', $mylonlat);
        $findlonlat = explode(',', $findlonlat);
        list($lng1,$lat1) = $mylonlat;
        list($lng2,$lat2) = $findlonlat;
        $EARTH_RADIUS=6378.137;
        $PI=3.1415926;
        $radLat1 = $lat1 * $PI / 180.0;
        $radLat2 = $lat2 * $PI / 180.0;
        $a = $radLat1 - $radLat2;
        $b = ($lng1 * $PI / 180.0) - ($lng2 * $PI / 180.0);
        $s = 2 * asin(sqrt(pow(sin($a/2),2) + cos($radLat1) * cos($radLat2) * pow(sin($b/2),2)));
        $s = $s * $EARTH_RADIUS;
        $s = round($s * 1000);
        if ($len_type > 1) { 
                $s /= 1000; 
        } 
        $distance = round($s/1000,2);
        return $distance;
}

$len_type 哪来的