Evan,
I don't understand the problem that you are describing.
... and is there any reason that you are applying rotations about each
axis sequencially? If not, then the whole idea of using axisangle is
to get a rotation about any arbitrary axis, such as [0.2, -0.4, 0.6],
that does not even have to unit length, and any arbitrary angle.
Lily Lee
>
> First of all thanks for your help, Lily Lee. AxisAngle is the solution to
> rotating about an object's coordinate system rather than the absolute
> coordinate system...
>
> However, I am still confused about something. Let's assume I carry out
> rotations about the x axis first, then about the transformed y axis, and
> finally about the transformed z axis. From my computer graphics text, you
> multiply the transformation matrix by your vector to get the transformed
> vector.
>
> For example, the matrix for rotation about the x axis is:
>
> 1 0 0 0
> 0 cos a -sin a 0
> 0 sin a cos a 0
> 0 0 0 1
>
> If I multiply this by the unit vector along the y axis, [ 0 1 0 1] T, then I
> get the vector [ 0 0 1 1 ] T, which is the unit vector along the z axis.
> This conforms to the right handed coordinate system and makes sense. What
> doesn't make sense?
>
> Let's say that I rotate my object around the absolute X axis by some
> arbitrary angle. I then should be able to rotate the unit vector for the Y
> axis by the same angle (we'll call this rotated vector Y'). I can then use
> AxisAngle to rotate about Y'.
>
> However, the above doesn't work! I have to multiply my Y unit vector by the
> X rotation matrix (instead of the other way around) to get this to work!
> Things get even crazier when I try to obtain Z'!
>
> To get Z' I multiply the Z unit vector by the 3x3 rotation matrix of my Y
> transform. However, to get this to work, I have to negate the x component
> of the vector!
>
> Can anyone explain why this is the way it is done?
>
> Thanks,
> Evan Drumwright
>
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