[info] newscientist: cheap, portable motion capture

[Alejandro Dubrovsky]

(
http://technology.newscientist.com/article/dn12963-cheap-sensors-could-capture-your-every-move.html
very nice demo video at:
http://www.youtube.com/watch?v=V0yT8mwg9nc
)

Cheap sensors could capture your every move
Movie Camera

 * 15:33 26 November 2007
 * NewScientist.com news service
 * Mason Inman

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A combination of movement sensors and ultrasound emitters might lead to
versatile motion capture systems for controlling computers


Video games like Dance Dance Revolution could soon require more than
just fancy footwork. Small, cheap sensors for tracking the movement of a
person's entire body could lead to "whole-body interfaces" for
controlling computers or playing games, researchers say.

Conventionally, motion capture makes use of reflective dots or small
LEDs attached at key points on a person's torso, limbs and head.
Capturing the movements of these points using an array of cameras allows
animators to create a computerized skeleton, which can then guide the
movements of an animated character, for example.

However, "these systems need controlled situations to work" and
typically cost tens of thousands of dollars, says Rolf Adelsberger of
the Swiss Federal Institute of Technology (ETH) in Zurich.

So Adelsberger and colleagues at ETH, along with researchers at
Massachusetts Institute of Technology (MIT), and Mitsubishi Electric
Research Laboratories, both in Cambridge, Massachusetts, US, set out to
create a cheaper, more versatile motion capture system that works
outside the lab or studio.

Their new motion capture sensors works even while a person is driving or
skiing (see video, top right). It could make computer animation or movie
effects more lifelike, the researchers say, and perhaps even help
doctors analyse movements of patients going through physical therapy.
Bat-like ability

Several sensors measuring about 2.5 centimetres on each side are
attached to a person's legs and arms. The sensors detect movement in two
different ways: accelerometers and gyroscopes measure motion, but
ultrasonic beeps are also emitted.

Tiny microphones mounted on the torso pick up these beeps, allowing a
laptop computer, carried in a backpack, to calculate the distance to the
sensor. The system is similar to, albeit much simpler than, bats'
ultrasonic echolocation, and together with the motion sensors provides a
more accurate overall picture of body movement. The small backpack also
holds the batteries that power the system.

"The sensors are all off-the-shelf parts," Adelsberger says, making the
system much cheaper than other motion-capture technology. It cost about
$3,000 currently, but this could come down to a few hundred dollars, he
says, if the sensors are mass-produced.
Active situations

In tests, the system compared well with a commercial motion capture
system called Vicon. It got the angles of the body's joints almost
exactly correct, but experienced some "drift", in which the system
erroneously thought that the body as a whole had shifted or rotated from
its actual orientation.

For Vicon to work, it requires a controlled, indoor environment and a
number of fixed cameras. The new system works in a variety of different
situations, for example, when someone is skiing or biking.

The new system does not work when people make very sudden movements,
however, because the relatively cheap sensors used are not yet accurate
enough to compensate. But they are quickly improving, Adelsberger says.

"I think the biggest impact of this system is in easier data collection
in everyday situations," says Christoph Bregler, an expert on motion
capture at New York University, US.

"This system could record many new activities for sports medicine,
behavioral studies [and other fields] that were impossible before," he
says.

Details of the project were presented at SIGGRAPH, a computer graphics
and interactive technologies conference held in San Diego, California,
US, in August.