I have read an article about Quaternion in this site by Diana Gruber.She said Quaternion are needn''t in game programming...... This is some word in her article: -> Question: Quaternion operations are faster because they can be done using fewer operations. Answer: Disregarding my informal proof that the minimum operation count will be exactly the same, don''t forget to consider the operation count in converting quaternions to a matrix format in order to make them compatible with DirectX or OpenGL, or to add translation information, for example. <- Is this exactly or unilateral? Especially the words "don''t forget to consider the operation count in converting quaternions to a matrix format in order to make them compatible with DirectX or OpenGL, or to add translation information." goddess just one...