[ODE] Determining relative orientation and angular velocity

[Marcus Brubaker]

Hi,

I'm trying to determine the orientation and angular velocity of an 
object relative to a reference orientation.  Specifically, I'm need to 
calculate the Euler angles (and their time derivatives) but instead of 
relative to the canonical orientation, relative to some specificied base 
orientation.  I know how to compute the regular Euler angles from a 
quaternion so I guess it's just a matter of getting the right quaternion 
and its time derivative.  Anyone have any suggestions?  Thanks.

Regards,
Marcus