PHP下的经纬度求距离

/***  @desc 根据两点间的经纬度计算距离*  @param float $lat 纬度值*  @param float $lng 经度值*/ function getdistance($lat1, $lng1, $lat2, $lng2) {     $earthradius = 6367000; //approximate radius of earth in meters      /*       convert these degrees to radians       to work with the formula     */      $lat1 = ($lat1 * pi() ) / 180;     $lng1 = ($lng1 * pi() ) / 180;      $lat2 = ($lat2 * pi() ) / 180;     $lng2 = ($lng2 * pi() ) / 180;      /*       using the       haversine formula       http://en.wikipedia.org/wiki/haversine_formula       calculate the distance     */      $calclongitude = $lng2 - $lng1;     $calclatitude = $lat2 - $lat1;     $stepone = pow(sin($calclatitude / 2), 2) + cos($lat1) * cos($lat2) * pow(sin($calclongitude / 2), 2);  $steptwo = 2 * asin(min(1, sqrt($stepone)));     $calculateddistance = $earthradius * $steptwo;      return round($calculateddistance); }