PLEASE READ: Terms for an extensive list of Motion-to-Sense MTS algorithms

Darren Kelly (
Tue, 14 Oct 1997 17:20:24 +0200 (MST)

A reminder to dance-tech, try to be a more precise describing what I call
MTS algorithms. I will try to collate more and will refer to them in my
CMJ article (with references), and so we need to get them straight:

r: position: a vector with three components. Where "it" is.

(the traditional symbol "r" comes from the word radius)

v: velocity: a vector with three components. How fast it
is moving (speed) AND the direction it is moving. This
seems to be what people mean by "movement". Something is
either moving (has velocity) or is not moving (zero velocity).

[please don't write back to tell me about Einstein]

a: acceleration: a vector with three components. You feel
this whenever your car _accelerates_ AND whenever your
car goes around a corner.

t: time: a scalar (a single number)

The motion of anything can, for our purposes, be completed specified
by the position vector as a function of time: r(t). The path a moving
object follows is know as the space-curve of the motion. An example
of a space-curve is the circle formed when you swing your arm around
in a circle. That's all you'll need to know to describe ANY motion.

Learning to exploit this incredibly simple representation is,
however, as complicated as the infinity of possible motions, and
requires the sort of training mathematicians and physicists suffer.

There is not necessarily any acceleration present just because something
is moving. If your car is travelling on a flat road at constant speed in a
contant direction it has a constant velocity (with respect to me, standing
on the side of the road). It is not, however, accelerating, even if
you have to keep your foot on the "accelerator" (gas pedal) to balance
the deceleration due to air pressure and friction. This is subtle, yet
important. It isn't subtle when you measure it !

If I can systematically collect accurate descriptions of all algorithms
people have found useful my article will form an understandable, accurate
reference of performance options written in appropriate language for all
to enjoy. Don't hesitate about trying to describe things physically, I
and others on dance-tech familiar with the maths and physics can sort
that out. Just try to describe your algorithms as carefully as possible,
and if I'm still in doubt I'll contact you (directly, not via dance-tech).

In addition, list the INPUT DEVICES (transducers, sensors, camera signals,
etc.) and the OUTPUT DEVICES (MIDI sound module, MIDI compatible light
modules, smoke machines etc.). And try to describe the type of dance
motion you use to exploit the setup.

And please include your dance company/collaboration/company so that
this, too, can be referred to in the CMJ article.

Of course I'd appreciate references to existing lists, and
in particular independently published articles.


PS: No, I won't mail this much every day.

Darren Kelly | | |
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