PHP计算百度地图两个GPS坐标之间距离的方法

/**
 * 计算两个坐标之间的距离(米)
 * @param float $fP1Lat 起点(纬度)
 * @param float $fP1Lon 起点(经度)
 * @param float $fP2Lat 终点(纬度)
 * @param float $fP2Lon 终点(经度)
 * @return int
 */
function distanceBetween($fP1Lat, $fP1Lon, $fP2Lat, $fP2Lon){
    $fEARTH_RADIUS = 6378137;
    //角度换算成弧度
    $fRadLon1 = deg2rad($fP1Lon);
    $fRadLon2 = deg2rad($fP2Lon);
    $fRadLat1 = deg2rad($fP1Lat);
    $fRadLat2 = deg2rad($fP2Lat);
    //计算经纬度的差值
    $fD1 = abs($fRadLat1 - $fRadLat2);
    $fD2 = abs($fRadLon1 - $fRadLon2);
    //距离计算
    $fP = pow(sin($fD1/2), 2) +
          cos($fRadLat1) * cos($fRadLat2) * pow(sin($fD2/2), 2);
    return intval($fEARTH_RADIUS * 2 * asin(sqrt($fP)) + 0.5);
}
/**
 * 百度坐标系转换成标准GPS坐系
 * @param float $lnglat 坐标(如:106.426, 29.553404)
 * @return string 转换后的标准GPS值:
 */
function BD09LLtoWGS84($fLng, $fLat){ // 经度,纬度
    $lnglat = explode(',', $lnglat);
    list($x,$y) = $lnglat;
    $Baidu_Server = "http://api.map.baidu.com/ag/coord/convert?from=0&to=4&x={$x}&y={$y}";
    $result = @file_get_contents($Baidu_Server);
    $json = json_decode($result);
    if($json->error == 0){
        $bx = base64_decode($json->x);
        $by = base64_decode($json->y);
        $GPS_x = 2 * $x - $bx;
        $GPS_y = 2 * $y - $by;
        return $GPS_x.','.$GPS_y;//经度,纬度
    }else
        return $lnglat;
}