The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008
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calibration and the system test accuracy are provided in the
results and analyses.
Figure 2. (a) An image of the spine of a project participant and
the imaging system. Note the round ink markers of the spine
anthropometric landmarks in (b).
2.2 Limb coordination in a rugby game lineout study
The research involves four stages, namely: 1) capture
stereovideo clips of a rugby lineout for virtual lineout display
on the white screen; 2) create 3D colour anaglyph video clips;
3) acquire players’ body segment movement; and 4) compute
parameters to determine the quality of limb coordination. Two
groups of ball throwers were recruited for the study. The
accurate throwers were elite and seasoned players while the
inaccurate throwers were occasional players.
2.2.1 Capturing stereovideo clip of a rugby lineout for a
virtual lineout scene
A NuView, SX-2000, Stereo3D camcorder adapter (Figure 3a)
developed by 1-0 Display Systems, Sacramento, California
was selected for the application. The device allows recording
of field-sequential video images of a rugby lineout throw
(Figure 3b) onto a DV tape or onto a computer hard drive. The
device uses a field-sequential technique to capture stereo
images using a single-lens DV. Accordingly, the device uses
mirrors to direct the incoming light rays onto the left and right
viewing windows. A set of alternating shutters allows the right
and left perspective view to be imaged onto the sensor as odd
and even fields. Hence, each frame of video footage consists of
a view from the left window as odd fields and a view from the
right window as even fields. Consequently, each frame can be
field-decoded (deinterlaced) to form left and right stereo
images.
(b)
Figure 3. a) NuView 3D imaging device; b) Scene of a rugby
lineout throw.
To capture the 3D video footage for the virtual lineout scene,
two standard 50 Hz DV cameras were placed perpendicular to,
and directly in front of each real lineout in order to estimate
where the optimal point in space was for the ball to be caught.
Also, a Sony HDV 50 Hz camera, with NuView, SX-2000,
Stereo3D camcorder adapter, was located directly in front of
the lineout at a height similar to that of a throwers head (Figure
4). The NuView 3D camera was approximately 5m behind the
sideline, 5m behind where the thrower would stand, for optimal
depth perception. This was determined through testing of the
NuView hardware as demonstrated by Chong and Croft (2005).
In the lineout simulation, thirty lineouts were performed to the
distances close to six (front jumper), 10 (middle jumper), and
14 (back jumper) metres as these were the distances estimated
to be where the two, four, and six jumpers would be in a real
lineout (Figure 4). The player formation was as follows: lifter,
jumper, lifter, jumper, lifter, jumper, and lifter, with the jumpers
entering the lineout at the nominated positions and the lifters
standing at even distances between these. The jumper and
lifters then performed each jump in their own time yet no balls
were actually thrown, rather the players were asked to imagine
one being thrown.