Rotate an existing quaternion around an axis?

Question

I have an existing quaternion (Java Quat4f). I would like to rotate this quaternion around an axis (i.e. 90 degrees around the x axis, 25 degrees around the y axis, 10 degrees around the z axis, 180 degrees around the y axis, etc.)

How can I rotate the existing quaternion around an axis?

Thank you!

Answer 1

To combine rotations, I believe you canjust multiply that quaternion with a quaternion for each of the other axis rotations you require.

For example, in this simple (extension) method I wrote, I get the final quaternion by combining 3 quaternions for X, Y and Z rotations.

    //Takes in angles in degrees
    //Useful wiki page: http://www.ogre3d.org/tikiwiki/Euler+Angle+Class and http://www.ogre3d.org/tikiwiki/Euler+Angle+Class+Mogre
    public static Quaternion ToOrientation(this Vector3 vec)
    {
        Quaternion xRot = new Quaternion(Math.DegreesToRadians(vec.x), Vector3.UNIT_X);
        Quaternion yRot = new Quaternion(Math.DegreesToRadians(vec.y), Vector3.UNIT_Y);
        Quaternion zRot = new Quaternion(Math.DegreesToRadians(vec.z), Vector3.UNIT_Z);
        return xRot * yRot * zRot;
    }

I must admit my knowledge of quaternions is not amazing, so any expansions on this answer would be appreciated.

Good luck! :)