   removing rotation about vertical axis
  Hi,I am not sure what i am about to ask is feasible but here it is. I am looking for a method for removing rotational component about a particlar axis (e.g. the y axis, so that the animation of a dancer spinning will be turned to an animation where the dancer simply stand in its place).At the moment I achieve this by firsting converting the quaternion rotation to euler angles and simply zero the y axis component (yaw) and convert it back into quaternion. This seems to work although singularity can appear and cause discontinuity in the data, and I believe i can work around it. However I am not comfortable with the whole conversion to euler angles idea because each rotational component is not independent of each other, does anyone have a better, more sound solution?thanks   
  you might have better luck with quaternion -> matrix conversions, then constraining the matrix, re-normalise it, and reconvert to quaternion. For examplequaternion -> 3x3 matrix -> force Y axis to (0, 1, 0) -> re-normalise -> convert back to quaternion.;  thank you.I decided in the end that this way of going about the problem is too problematic, and I am going approach it differently.