I am having trouble with rotating models using quaternions/matrices. The model has three vectors to determine which way it is facing and a quaternion to store the rotation of the model. It also has a vector to store its position. When I rotate the model around the x axis the direction vector rotates clockwise and the quaternion rotates anti-clockwise. If I use negative x values for the direction vector then when I rotate the model around the y axis sometimes the vector and the quaternion rotate the same way and some times opposite ways. Can anyone give me any ideas as to why this happens? Thanks a ton - Gareth

I assume your 3 facing vectors are an up, facing and side vector for the model. Try negating your side vector (usually calculated from a cross-product, just do it the other way around because aXb = -bXa) to flip the "handedness" of the resulting orientation vectors.

Either that or use the quat conjugate q* = (w, -x, -y, -z) in the quat part.

Don''t try both at once though because they should cancel each other out!

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