/**计算两点的距离:
 *
 * @param $Y a的经度
 * @param $X a的维度
 * @param $bY 目标经度
 * @param $bX 目标维度
 *
 * @return float km
 */
function getJuli($aY, $aX, $bY, $bX)
{
    $earthRadius = 6367000; 
    $aY = ($aY * pi()) / 180;
    $aX = ($aX * pi()) / 180;
    $bY = ($bY * pi()) / 180;
    $bX = ($bX * pi()) / 180;
    $distanceX = $bX - $aX;
    $distanceY = $bY - $aY;
    $stepOne = pow(sin($distanceY / 2), 2) + cos($aY) * cos($bX) * pow
        (sin($distanceX / 2), 2);
    $stepTwo = 2 * asin(min(1, sqrt($stepOne)));
    $calculatedDistance = $earthRadius * $stepTwo;
    return round($calculatedDistance) / 1000;
}