Biomedical Engineering Reference
In-Depth Information
13.3.1 Setup
As described in the introduction of this chapter, virtual reality systems are the only
way to control all the parameters of the displayed situation. Indeed, the animation
of the kicker as well as the trajectory of the ball must be completely controlled to
change only one parameter at a time. Nevertheless, in that study, the displacements
of the goalkeeper must be the core of the Virtual Reality system designed for this
experiment. Indeed, the goalkeeper must be able to see the situation from different
viewpoints going from the two goalposts to any position in the goal. Moreover, when
the ball is kicked, the system must allow the goalkeeper to dive to intercept the ball
and to evaluate his performance.
13.3.1.1 Hardware Setup
To allow a complete freedom of movement of the goalkeeper, the stereoscopic vision
was ensured by the Nvidia 3D vision system at 120 Hz. This system is composed
of wireless glasses and USB infrared emitter. These glasses are similar to normal
ones and are maintained with a headband attached to the arms of the glasses. Thus,
participants are fully free of their movements. In addition, contrary to HMD devices
for example, the goalkeepers can also see their body segments such as their arms that
are really important for such intercepting tasks. These glasses are synchronized with
an Acer high frequency H5360 video projector. Rear projection was done to avoid
shadows since the goalkeeper was placed near the screen to have a very large field
of view. In front of this screen, a real goal was placed on synthetic grass to allow
the immersed goalkeeper to feel the pitch and to dive as realistically as possible
(Fig.
13.5
).
The viewpoint used in the simulation was modified according to the head move-
ment. Five markers were indeed placed on a hair band to record the head's position
via the Vicon MX motion capture system. This latter was coupled with the Autodesk
Motionbuilder software in order to update in real time the player's viewpoint as well
as handling the stereoscopic vision.
13.3.1.2 Virtual Kicker and Ball Animations
Kicker animation was based on captured motions (see [
16
] for detailed information
on the motion capture session). Real free kick situations were captured using the
optoelectronic motion capture Vicon MX camera system at 300 Hz. The participants
were mid-level football players. They had to kick the ball in a zone of 1.7 m * 1 m
in the top corner of the net avoiding a plastic wall of five players. The ball was
positioned at 20 meters from the goal and aligned with the left goal post (Fig.
13.4
).
Successful motions were kept for animation.
Concurrently, the initial linear and angular velocities of the ball at kick were
captured by using reflective tapes on the ball. In addition to the final position of
