Quaternions

Here's a web site that provides a lot of useful information about converting between the various rotation orientation representations:

My limited understanding of the math is that you may not be able to avoid the Euler singularities.

-Wayne

As you know, Eulers have an order, like XYZ, YXZ, ZYZ, etc. . Simply convert your Quaternion into XYZ, throw away the Y and Z, then convert into YXZ, throw away the X and Z, finally convert into ZXY, and throw away the X and Y. You will get the error in the X, Y, and Z from the three previous operations. Of course, you can not get the original rotation beck from these... .

Oh yeah, I forgot to mention my reasoning for converting to Euler angles is this - I am using this on an airplane for which I am controlling rotation about the z-axis with the rudder, rotation about the y-axis with the elevator and rotation about the x-axis with ailerons. If I use Euler angles, I can have an error which relates to each one of the control surfaces (i.e. if my yaw error is large, then I know I have to give full rudder deflection). However, if my quaternion error is large...it's not quite clear to me how I would translate that into rudder, elevator, and aileron deflection. Does anyone know of a way?

Thanks

Well, isn't this relevant for small errors only ?

If you have a 180° yaw error, are you going to turn with the rudder only ?

If you have a 160° yaw error and also 45° roll, will you first make the plane horizontal and then turn 160° with the rudder, or will you use the existing roll to turn 200° with the elevator ?

AC

I am trying to pull off autonomous hovering with a fixed-wing aircraft in the "nose-up" position (pitch=90, yaw=0). Therefore, if I have errors of more than, say 30 degrees, it will not be able to maintain this attitude. So...yes, I am only hoping to have small errors :-)