PHPで経度と緯度から距離を計算する

/***  @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); }