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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