PHP根据两点间的经纬度计算距离

/**  
*转载自：http://www.jb51.net/article/56967.htm
* @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 
$lat1 = ($lat1 * pi() ) / 180; 
$lng1 = ($lng1 * pi() ) / 180; 
$lat2 = ($lat2 * pi() ) / 180; 
$lng2 = ($lng2 * pi() ) / 180; 
$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); 
} 
$limit = getDistance("39.976315","116.492302","39.976315","116.492302");
echo $limit;