   Unknown rotation defenition
  Hi,I am ripping 3D models from the game Faces of War for education purposes.In the animation files I encounterd rotations, stored as 3 floating point values. After a lot of experiments it seems the numbers represent a 3D vector. The rotation is defined as a rotation around this vector (as an axis). However, the angle to rotate around this axis is not just the length of the vector, but seems to be arccos( 1 - 2 * length^2 ). Has anyone any idea why someone would choose such a format? I could not link it to quaternions either, altough I'm not very familiar with quaternions.Thnx a lot,greatz, Dietepiet   
  Wild guess.length = va DOT vaso you'd have 1 - 2*lengthTranslated, it should work well without additional computations.   ;  I agree that using the square of the length is computationally cheaper. But I don't really see where you left the arc-cosine. After all, that’s not really what you call a cheap operation. Maybe it’s easy to construct the corresponding rotation matrix using this format, but I can’t see why.   