/** 
* @desc 根据地址获取经纬度 
* @param string $addr 地址 
* @param string $city 地址所在城市 
* @param string $ak 百度api密钥 

*/

function GetLN($addr = '',$city = '',$ak = ''){
   
   $addr = urlencode($addr);
   $api_url = "http://api.map.baidu.com/geocoder/v2/?address=$addr&city=$city&output=json&ak=$ak"; 
   $json = file_get_contents($api_url);
   $json_arr = json_decode($json);

}

/** 
* @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); 
}