四元数的优势： 三维空间的旋转完全可以由4元数来胜任。传统意义上需要3×3矩阵来进行向量的旋转（4x4矩阵的第四列表示平移）。所以四元数更节省空间，运算速度更快。既然四元数能方便的表示3D旋转，那么对他们进行插值就能产生平滑的旋转效果。-Quaternion advantages: the rotation of three-dimensional space can count from $ 4 to do the job. Traditionally need 33 for vector rotation matrix (4x4 matrix fourth column represents the pan). So quaternion more space-saving, faster operation. Since quaternion can easily represent 3D rotation, then they will be able to produce a smooth interpolation rotation effect.