Nancy.Hamilton writes:

>I happened to be watching Dateline NBC last night and saw a motion recordin=
>system that blew me away. The system consisted of sensors taped to various
>points on a dancers body (looked like duct tape - no mention of what type o=
>sensors), then attached to an overhead cable system which was connected to =
>large bank of input devices of some type called a "flock of birds"

The system you saw is manufactured by Ascension Technology and works using
a DC magnetic field. Each "sensor" attached to the body montiors 6 degrees
of freedom (3 translation and 3 orientation). These systems (a competing
one is manufactured by Polhemus) are used extensively in virtual reality
applications. We are in the process of implementing the use of the "Flock"
for measurement of human segmental motion during a postural control task.
The system is built for sampling via an RS232 port (PC, MAC or Unix
Workstation) and can sample up to max of 144 Hz.

The systems vary in number of sensors, range, number of transmitters, etc.
But a 4 "sensor" system with a range of =B13ft runs about $8500.

The company can be contacted at:

Ascension Technology
PO Box 527
Burlington VT 05402


--Vernon McDonald

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Vernon McDonald Motor Performance Lab.
KRUG Life Sciences NASA/Johnson Space Center
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