Table 2: Three models for detecting the horizontal position
of the hit point.
Figure 8: Visualization of shot direction percentage from
the right front area of the court. The shot directions detected
from the G-model (left), GD-model (center), and DD-model
(right) are visualized using heat maps. The yellowish region
indicates the most likely location of the endpoint of the shot
direction.
5.5 Limitations in this Research
This section describes the limitations of the detection
accuracy and the primary cause of error in this study.
It is difficult to detect hit timing in a single frame
using this research method. This is because the output
information (hit timing) is not uniquely determined
from the time-series changes in the input information
(movement trajectory and skeletal information).
Therefore, applying this method to tactical analysis is
difficult, which requires hit timing accuracy on a
frame-by-frame basis.
The primary cause of error in the experiment de-
scribed in Section 5.2 is the irregular movement of
players in hit timing. In this study, the following hy-
potheses are formulated for the movement trajectory
and skeletal information, respectively, as the regular
movements of the players.
!
• The player moves away from the base around
the hit timing and returns to the base again.
• At the hit timing, the player's wrist is farthest
away from the waist.
Therefore, detection errors are likely to occur when
players' movements that do not conform to the above
hypotheses (irregular movements) are observed.
We have attempted to reduce the number of errors
by applying the additional detection described in Sec-
tion 4.2, but we have not been able to address all er-
rors.
6 CONCLUSIONS
This research proposes a method for detecting shot in-
formation using badminton players' footwork trajec-
tories and skeletal information. The proposed method
detects the hit timing using the time series information
of the footwork trajectory and skeletal information,
which are characterized by the hit timing. Further-
more, this method detected the horizontal position of
the hit point using the footwork trajectory around the
hit timing. As a result of the demonstration experi-
ment, the hit timing detection accuracy (F-measure)
for the player at the front court was 95.9%, and the
horizontal position of the hit point was detected with
an accuracy of MSE=54.0. Using the detected data,
we quantitatively and qualitatively evaluated that the
tactical analysis can be performed at the same level as
the ground truth. As a future work, we plan to expand
the experimental data. We will confirm the generality
of the method from the results of tests using players'
data that are not included in the training data. We will
also investigate how players' playing styles and other
factors affect detection accuracy.
This method can automatically detect data for tac-
tical analysis using only the player's footwork trajec-
tory and skeletal information from the monocular
camera images. In conclusion, this research suc-
ceeded in solving the problem of the conventional
method using shuttle tracking and in automating the
data collection for badminton video analysis.
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