[sdiy] proximity detectors anyone ?

[jbv]

Hi list,

today an idea arose during a conversation with friends...
It began with proximity detectors used in robotics, and
especially the fact that those sensors are used on a moving
device to detect non-moving objects of the environment in
order to avoid them...
but what if the idea was reversed : fixed detectors to detect
distance of moving objects ? for instance 6 detectors, each
one on 1 side of a cube, and moving objects in between
(a moving hand, balloons, bubbles, a butterfly, flies,
smoke, whatever). Signals sent by detectors would be
hooked to a uC to compute in realtime the xyz position of
the moving hand, and these parameters would be used as
VC signals for synths...
in the case of a hand, I guess a joystick or a dataglove could
also be used to determine xyz position in space, but I'm sure
there are many other funny applications...

so here's my question : does anyone have any experience with
proximity detectors, and what would be the best choice : IR,
ultrasonic...
I've already found several papers on the subject via google, but
I'd like to have the opnion of this list as well...

Best,
JB