## 4 Results and Discussion
### Experimental Results
A video for this work is available at the link ([[https://www.youtube.com/watch?v=FBN5](https://www.youtube.com/watch?v=FBN5)]([https://www.youtube.com/watch?v=FBN5](https://www.youtube.com/watch?v=FBN5)) XctaAXQ (accessed on 18 January 2021)). The number of frames in which the target person is correctly tracked to the total number of frames in the course is called the successful tracking rate [9]. The average successful tracking rate over all the experiments was 62%, while the lost tracking frame rate was 38%. The lost tracking rates were due to the disappearance of the target person around the two corners and the sensor noise during the tracking state. The average frame rate was 24.4 frames/s, that is there were 40.98 ms between each frame in the real-time video, which corresponded to the specifications of the camera used. The average distance traveled by the robot and the time when the target was lost were 3.95 m and 12.13 s at the first corner and 15.31 m and 33.84 s at the second corner, respectively. The average distance and time when the target was recovered were 6.71 m and 17.66 s at the first corner and 19.01 m and 40.75 s at the second corner in each experiment, respectively. A comparison of the recovery time, distance, and velocity for recovering the target person at the two corners is shown in Figure 10a. The recovery time is the duration from the moment the target was lost to his/her recovery. The recovery distance and recovery velocity are defined similarly (Figure 6b,c). The average recovery distance, recovery time, and recovery velocity to recover the target to the tracking state after the disappearance of the target from the FoV of the camera were 2.76 m, 5.52 s, and 0.50 m/s at the first corner and 3.70 m, 6.91 s, and 0.53 m/s at the second corner, respectively. Although the velocity of the robot around the second corner was faster than that at the first corner, the recovery time was longer because of the longer recovery distance around the second corner. The nature of the geometric structures and the target's walking played a major role in the robot movement and the time consumed. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline  & **Performance Measures** & **Exp.1** & **Exp.2** & **Exp.3** & **Exp.4** & **Exp.5** & **Exp.6** & **Exp.7** & **Exp.8** & **Exp.9** & **Exp.10** & **Total** & **Average** & **Std** \\ \hline \multirow{7}{*}{**Overall**} & Experiment success & O & O & O & O & O & O & O & X & O & O & 90\% & - & - \\ \cline{2-13}  & Target’s travel distance (m) & 24.4 & 23.9 & 25.0 & 24.9 & 23.5 & 24.1 & 23.6 & 15.0 & 23.8 & 23.6 & 23.1 & 23.2 & 2.92 \\ \cline{2-13}  & Robot’s travel distance (m) & 22.0 & 22.8 & 22.2 & 22.3 & 22.1 & 22.0 & 22.4 & 22.2 & 22.0 & 21.4 & 22.4 & 22.6 \\ \cline{2-13}  & Robot’s travel time (s) & 45.3 & 45.5 & 49.6 & 48.2 & 51.7 & 47.3 & 47.8 & 41.3 & 47.1 & 51.5 & 47.5 & 47.6 & 3.10 \\ \cline{2-13}  & Robot’s average velocity (m/s) & 0.49 & 0.50 & 0.45 & 0.46 & 0.43 & 0.47 & 0.47 & 0.34 & 0.47 & 0.43 & 0.45 & 0.45 & 0.04 \\ \cline{2-13}  & No. of frames & 1092 & 1143 & 1171 & 1220 & 1210 & 1149 & 1171 & 102  
The x-y coordinates of the target and robot trajectories were generated while the robot was following the target. The trajectories were almost identical, as shown in Figure 10b. The letters S and E refer to the start and end of the trajectories, respectively. The blue dotted curve and the green curve represent the trajectories of the robot and the target, respectively. The empty green and filled blue circles represent the target position (TP) and the robot position (RP) at the LOP at the corners during the tracking state (Figure 6a for the side view), respectively. The empty black and filled red circles respectively represent the locations of the robot and the target person at the first frame where the target was successfully re-tracked after the target had disappeared from the FoV of the camera (Figure 6c for the side view).