https://ingun37.wordpress.com/2013/07/02/quaternion-%ED%9A%8C%EC%A0%84%EC%9D%84-%ED%8C%8C%EC%9D%B4%EC%8D%AC%EC%9C%BC%EB%A1%9C-%EA%B5%AC%ED%98%84%ED%95%9C%EA%B2%83/
