php根据两点经纬度算距离

/**
 * 计算根据两点间经纬度计算两点间距离
 * @param unknown $lat1
 * @param unknown $lng1
 * @param unknown $lat2
 * @param unknown $lng2
 * @return number  /Km
 */
function getDistance($lat1=0, $lon1=0, $lat2=0, $lon2=0){
    //将角度转为狐度
    $radLat1=deg2rad($lat1);//deg2rad()函数将角度转换为弧度

    $radLat2=deg2rad($lat2);

    $radLng1=deg2rad($lon1);

    $radLng2=deg2rad($lon2);

    $a=$radLat1-$radLat2;

    $b=$radLng1-$radLng2;

    $s=2*asin(sqrt(pow(sin($a/2),2)+cos($radLat1)*cos($radLat2)*pow(sin($b/2),2)))*6378.137;

    return $s;
}