[Algorithms] Rotation about arbitrary axis

[Pierre T. <p.t...@wa...>]

Hi,

Since I needed a piece of code to do that I searched the web and found:
http://www.iuk.tu-harburg.de/hypgraph/modeling/mod_tran/3drota.htm

I used the final matrix at the bottom of the page, but it seems to fail when
the arbitrary axis actually is the Z axis. The third column gets erased
where it should at least contain a 1. This is obvious when looking at the
provided matrix, since the third column of the third row depends on the
rotation angle - and of course if the input axis already is the Z axis, it
shouldn't.

Now, it sounds normal regarding the underlying method (mapping the rotation
axis to Z, etc). But I wonder whether there's an easy way to perform a real
arbitrary rotation about any arbitrary axis without using different code
paths according to the input axis.

I think it can probably be done by introducing quaternions or better,
angle-axis, in the story. But err.... maybe there's something simpler.

Pierre