php计算两个坐标直线距离

 function rad($d)
 {
        return $d * 3.1415926535898 / 180.0;
 }
 function GetDistance($lat1, $lng1, $lat2, $lng2)
 {
     $EARTH_RADIUS = 6378.137;
     $radLat1 = rad($lat1);
     //echo $radLat1;
    $radLat2 = rad($lat2);
    $a = $radLat1 - $radLat2;
    $b = rad($lng1) - rad($lng2);
    $s = 2 * asin(sqrt(pow(sin($a/2),2) +
     cos($radLat1)*cos($radLat2)*pow(sin($b/2),2)));
    $s = $s *$EARTH_RADIUS;
    $s = round($s * 10000) / 10000;
    return $s;
 }