# Investigating a Toolchain from Trajectory Recording to Resimulation
## 4 Discussion  
There are two major limitations that have been mentioned in Section 3, i.e., the estimation of velocities from the recorded data and the behavioral models within the traffic simulation. These are discussed in more detail in this section.  
The data capture using a camera have to be optimized with respect to the derivation of the velocity, especially for pedestrians. Due to the angle of exposure and the transformation into a plane, the pedestrians in the pictures are distorted. That makes it difficult to calculate the correct center point for the trajectory. Therefore, it is recommended to optimize the calculation of the pedestrian center points. The calculation of the car's center points also needs improvement. Additionally, the methods for smoothing the velocity estimates need to be refined.  
In the version of the traffic simulator openPASS used in this research, pedestrians are only implemented very simply and without a behavior model. They follow predefined trajectories without reacting to the surrounding traffic. Thus, only the behavior of the vehicles can be examined for a replication of the recorded trajectories as they react to the pedestrians movement.  
Further, an interesting traffic scenario could not be considered for this research because of limitations in the simulator, i.e., overtaking maneuvers in the proximity of the T-junction with traffic on both lanes. The issue is that the OpenDrive standard only specifies a single direction of travel for each lane. The modeled T-junction describes traffic from all directions towards and away from the intersection, according to their lanes. Thus, it is not possible to model an overtaking maneuver and traffic on both lanes at the same time considering defined driving directions on the lanes relative to the defined reference line in the OpenDrive standard. The reference line takes the geometry of the road, while the lanes are defined next to this line. The driving direction on the lanes is defined by a sign and a number. In the direction of the reference line, the lanes are numbered ascending and negative (\(-1\), \(-2\), \(-n\)), while the lanes are correspondingly ascending positive (\(1\), \(2\), m). For this reason, a workaround for the used OpenDrive standard is proposed.  
The idea is to define overlaying roads with different driving directions and no connectors on the crossing as they are defined in the standard. For all possible routes on the t-crossing from the start to the end of the route, a road with the corresponding reference line and two lanes according to the driving direction on the route is defined; see Figure 10. This realization defines an OpenDrive-based file that includes all possible driving directions on the T-junction, and respective openPASS simulations are able to interpret the scenario.  
It should be mentioned that for larger scenarios with more than one intersection and a more complex routing, this kind of workaround may not be practical. Furthermore, more research and development is needed for the proper interpretation of the respective OpenScenario files within openPASS.  
However, for investigating single scenarios on intersections or parts of roads, it seems to be a suitable way to enable a more realistic application of the open-source simulation platform openPASS. It offers the possibility to define an intersection scenery and, at the same time, simulate traffic from any possible direction on arbitrary lanes in openPASS. Although the defined agents drive on roads with different IDs, they recognize each other and react in the way defined by the behavioral models.  
\begin{table}
\begin{tabular}{c l c c} \hline \hline
**Scenario** & & **RMSE [m/s]** & **RMSE DNN [m]** \\ \hline
1 & Car 1 (front) & 1.046 & 0.381 \\  & Car 2 (following) & 3.048 & 0.470 \\ \hline
2 & Car 1 (LTAP) & 3.791 & 2.049 \\  & Car 2 (straight) & 3.189 & 9.373 \\ \hline
3 & Car (straight) & 2.183 & 0.564 \\  & Pedestrian (crossing) & 1.378 & 0.269 \\ \hline \hline \end{tabular}
\end{table}
Table 4: RMSE of velocities for the three scenarios.