php计算两个坐标（经度，纬度）之间的距离

php计算两个坐标（经度，纬度）之间的距离，返回结果为米或者千米

function distance($lat1, $lng1, $lat2, $lng2, $miles = true)
{
	$pi80 = M_PI / 180;
	$lat1 *= $pi80;
	$lng1 *= $pi80;
	$lat2 *= $pi80;
	$lng2 *= $pi80;
 
	$r = 6372.797; // mean radius of Earth in km
	$dlat = $lat2 - $lat1;
	$dlng = $lng2 - $lng1;
	$a = sin($dlat / 2) * sin($dlat / 2) + cos($lat1) * cos($lat2) * sin($dlng / 2) * sin($dlng / 2);
	$c = 2 * atan2(sqrt($a), sqrt(1 - $a));
	$km = $r * $c;
 
	return ($miles ? ($km * 0.621371192) : $km);
}