PHP计算两个经纬度之间的距离

*  @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);  
 }