php计算两个坐标（经度，纬度）之间距离的方法

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);
}