/**
 * [getDistance description]根据两点的经纬度计算距离
 * @param  [type] $latitudeOne  [description]第一个点的纬度
 * @param  [type] $longitudeOne [description]第一个点的经度
 * @param  [type] $latitudeTwo  [description]第二个点的纬度
 * @param  [type] $longitudeTwo [description]第二个点的经度
 * @return [type]               [description]返回距离
 */
function getDistance($latitudeOne,$longitudeOne,$latitudeTwo,$longitudeTwo){
        $earthRadius = 6378137; //地球半径

        $latitudeOne = ($latitudeOne * pi()) / 180;
        $longitudeOne = ($longitudeOne * pi()) / 180;

        $latitudeTwo = ($latitudeTwo * pi()) / 180;
        $longitudeTwo = ($longitudeTwo * pi()) / 180;

        $calcLongitude = $longitudeTwo - $longitudeOne;
        $calcLatitude = $latitudeTwo - $latitudeOne;

        $stepOne = pow(sin($calcLatitude / 2),2) + cos($latitudeOne) * cos($latitudeTwo) * pow(sin($calcLongitude / 2), 2);
        $stepTwo = 2 * asin(min(1,sqrt($stepOne)));
        $calculateDistance = $earthRadius * $stepTwo;

        $kilometer = round($calculateDistance / 1000,1); //得出的$calculateDistance是米为单位，这里除1000得到km,四舍五入到小数点一位数；

        return $kilometer;
}

$res = $this->getDistance(13.361389,38.115556,13.361389,38.125566);
var_dump($res); //答案是1.1