Fernando Gonzalez del Cueto wrote:
> I think it's pretty evident that the left
> reorientation scheme is much
> smoother than the other one.
>

In the following, assume your plane/ body is facing the +z direction.

In aviation, they talk of pitch (rotate x), yaw (rotate y), and roll (rotate
z).  Pitch and yaw are (over the long term) an inevitable consequence of
WHERE YOU'RE GOING.  Roll is a factor of comfort.  Even watching "Top Gun,"
 you'll see that the pilots may go through all kinds of stunts with rolls
when changing direction, but for long term travel toward a destination
(once they've completed a turn), they choose the orientation of the craft
on the right: ZERO ROLL.  Watch birds: they'll roll on a turn but choose
zero roll once they're pointed in the direction of choice.  We also design
our roadways to minimize roll;  yaw is an inevitable function of where
you're going; an effort is made to reduce pitch somewhat but it's rarely
eliminated.

http://liftoff.msfc.nasa.gov/Academy/ROCKET_SCI/SHUTTLE/ATTITUDE/PYR.HTML
http://www.bmfa.org/faq/flight_controls.htm

Similarly, if you're watching home videos, you're going to get more nauseous
with a camera that has done rotate z than you will with rotate x or y. A
common camera trick is to have the camera say no (yaw) or yes (pitch).  In
a typical day, your head & waist go through hundreds of rotate x's of tens
of degrees, but rotating your waist about the z axis is *uncomfortable* to
say the least.

These are the intuitive, aesthetic reasons why I disliked the roll inherent
in the as-written Reorient macro.   This is actually the reason I stopped
doing flocking animations a while ago: I knew that a bird or plane wouldn't
rotate in this fashion. I just this month figured out a solution when I hit
this wall with my camera reorientation.  The solution is a two step one.
That NASA link suggested that the rotations are always done in order of
Pitch, Yaw, and Roll.  My intuition is that one could tweak the macro
itself to affect the change I'm talking about-- perhaps even avoid the
abrupt change  you noticed.  While I'm tinkering, I'm publicly asking if
anyone else has figured this out.

Greg M. Johnson


>
>That might help you to choose.
>
>Good luck,
>
>Fernando
>

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