## 6 Experimental Results
### Results of the Docking Experiments  
First, we analysed the path deviation between a real trajectory of the bus and the path planned by our system. Table 4 presents the numerical values of that deviation for 50 sequences, where the bus stopped under the charger for which our system is operating. The deviation was calculated as Absolute Trajectory Error, where in this scenario, ATE is the Euclidean distance between the real and planned trajectory computed for each corresponding pose, and it is averaged over the entire trajectory. This type of error measures both the inaccuracy of the system when the driver follows the system's  
As can be noted, the error values differ significantly across multiple sequences. However, for all of them, the displacement value was small enough not to cause the re-planning of a reference trajectory. This means that only a single path was generated by the motion planner for each of the considered trials, which has an important advantage in terms of computational complexity. Unfortunately, the drawback of this approach is that in case the driver does not follow the system's suggestions from the very beginning, the RMS value of error will typically stay in the range of 0.5-1.0 m. This is the case for almost all the results in the considered table. However, all of these 50 sequences were successful, which naturally indicates that many various paths can be considered correct, as long as the final part of the trajectory leads to the charger's head. From this perspective, the more important indicator of the system performance seems to be the displacement value at the very end of a manoeuvre, as described in Section 6.3.  
The examples of two trajectories, recorded during the docking manoeuvre, are presented in Figures 13 and 14. What we observe is that the accumulated tracking error for all 50 sequences has a peak from around 25 m to the charger. At that distance, the drivers preferred to follow a different path (shorter to target) compared to the one proposed by the planning system (putting the bus straight to the target as soon as possible). Unfortunately, as the system was working in the background, we are neither able to confirm nor deny if there are different preferences among the tested drivers. Moreover, it might be the case that the drivers are concerned about the charging manoeuvre when they are closer to the desired charging location compared to the planning path window. Naturally, the tracking error between the taken path and the path proposed by the system is slowly converging to zero as both paths approach the desired charging location.  
lateral position margin wide enough for the used electric charger technology. Moreover, the obtained errors would still allow for a successful docking with other chargers having lower docking tolerances, e.g., Shunk chargers used in [3], making the proposed solution viable for a wide range of charger-pentograph choices.  
The errors for all of the docking runs are reported in Table 5 with statistical means presented in Table 6.  
Figure 14: Reference and real path of the bus, generated for the bus approach to the charging station. The point (0, 0) is the charger location (**A**). The Absolute Trajectory Error between the reference and real trajectory over time (**B**). Plots present the results for sequence 12.  
Figure 13: Reference and real path of the bus generated for the bus approach to the charging station. The point (0, 0) is the charger location (**A**). The Absolute Trajectory Error between the reference and real trajectory over time (**B**). Plots present the results for sequence 42.  
at that distance. The reason for this might be that the proposed path was less convenient or required a change in the driver's habits.