Re: motion tracking

Darren Kelly (kelly@x4u2.desy.de)
Thu, 16 Oct 1997 15:13:43 +0200 (MST)

On Wed, 15 Oct 1997, Christopher Sumpton wrote:
> all of the "motion tracking" technology works by measuring the change
> in position of the body in question. the system is normalized. the

No, if you stand "still" (which we know one can't, but whatever) wearing
EM tracking sensors (which are usually triad coil receivers) the position
data is still delivered. I don't see what you mean. Most implementations
measure both position and velocity simultaneously, maybe this is confusing
you. Whether or not the sensor is moving you still get, at each time
step, the position and velocity of the sensor [ r(t), v(t) ]. When the
sensor is still you get [ r(t), v(t) = 0]. When the sensor is moving you
get [ r(t), v(t) ], where r(t) is changing and v(t) is non-zero. For example:

At time t1: coordinates are [ r(t1) = 12, v(t1) = -2 ]
At time t2: coordinates are [ r(t2) = 10, v(t2) = -1 ]

where the velocity is in spatial units per time step. Note that the
velocity is also changing, i.e. that an acceleration is present.

> system is in flux. what is the change in measurement? that
Which system ? The sensors ? The EM field is certainly in flux (cycled),
but that is a different matter.

Darren

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