/**

• 计算两个坐标（经度，纬度）之间距离
  /
  public static 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);
  }