On 10/04/2003 02:28 PM, Michael Edmiston wrote:
> If there is no good reason to choose otherwise, I prefer to orient
> the coordinate system so positive-x is to my right, positive-y is in
> front of me, and positive-z is up.
Not meaning to dispute matters of taste, let me point
out that in the field of aeronautical engineering there
is another choice that many people find quite tasty:
-- The +x axis points forward out the nose of the
aircraft. This is also called the 12:00 direction.
-- The +y axis points out the right wing.
-- The +z axis is perpendicular to the other two,
such that xyz is right-handed, meaning it points
out the belly of the aircraft.
This has quite a number of convenient properties:
*) Motion in the +x direction is forward.
*) A positive rotation in the xy plane corresponds
to a positive yaw angle. This agrees with conventional
compass-type angles, i.e. measured CW from 12:00 as
seen from above.
*) A positive rotation in the yz plane corresponds
to a positive bank angle, raising the left wing.
*) A positive rotation in the zx plane corresponds
to a positive pitch angle, i.e. nose-up. (Note the
use here of the zx plane, not the xz plane, in
accordance with the cyclic rule: x->y->z->x....)
It's slightly icky to have the +z direction pointing
downward when the aircraft is in normal level-flight
attitude, but that seems like a small price to pay
for having everything else work out so nicely.