# Utilization of Quasi-Zenith Satellite System for Navigation of a Robot Combine Harvester
## 4 Discussion  
### Static Experiment  
The results from Table 2 imply that concerning the activation times there is not too much difference between three positioning augmentation systems. Although there might be some special cases in which factors like geography or weather conditions might affect these activation times, for implementation in a robot combine harvester it is safe to conclude that under normal operation conditions it should take less than 3 min to have any of these positioning systems ready. Figure 4(a) verifies that the scattered area of the points logged by the RTK positioning augmentation system has a small size. Figure 4(b) shows small variations in position over time, which indicates that it is possible to use the mean position logged by the RTK to neglect these small variations while using the RTK position data as a reference. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Positioning** \\ **Augmentation** \\ \end{tabular} } & \multicolumn{3}{c}{**RMSE of Lateral Deviation from**} & \multicolumn{3}{c}{**RMSE of Lateral Deviation from**} \\  & \multicolumn{3}{c}{**1 st Path (m)**} & \multicolumn{3}{c}{**2 nd Path (m)**} \\ \cline{2-9}  & **10:00** & **12:00** & **14:00** & **16:00** & **10:00** & **12:00** & **14:00** & **16:00** \\ \hline MADOCA & 0.11 & 0.04 & 0.07 & 0.08 & 0.36 & 0.69 & 0.63 & 0.67 \\ RTK & 0.23 & 0.09 & 0.08 & 0.09 & 0.58 & 0.66 & 0.58 & 0.66 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results from robot combine harvester controlled by MADOCA. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Positioning** \\ **Augmentation** \\ \end{tabular} } & \multicolumn{3}{c}{**RMSE of Lateral Deviation from**} & \multicolumn{3}{c}{**RMSE of Lateral Deviation from**} \\  & \multicolumn{3}{c}{**1 st Path (m)**} & \multicolumn{3}{c}{**2 nd Path (m)**} \\ \cline{2-9}  & **10:00** & **12:00** & **14:00** & **16:00** & **10:00** & **12:00** & **14:00** & **16:00** \\ \hline CLAS & 0.03 & 0.03 & 0.03 & 0.03 & 0.26 & 0.21 & 0.31 & 0.27 \\ RTK & 0.07 & 0.11 & 0.11 & 0.09 & 0.22 & 0.19 & 0.28 & 0.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results from robot combine harvester controlled by CLAS. The result shown in Figure 5(a) gives the initial idea that this positioning augmentation system is more accurate than MADOCA. The result shown in Figure 5(b) suggests that the loop shown in the MADOCA plot might be caused by an oscillation in the coordinates received until they converge to a smaller area of around 0.50 m by 0.50 m and the measurement stabilizes. For both the 2 DRMS and the CEP, a big value means that most of the position points are scattered over a wide area and a smaller value means that the position points are concentrated within a small area. The calculations from Table 3 verify the initial idea from Figure 6; the CLAS positioning augmentation system is more accurate than MADOCA. The average number of satellites tracked gives an indication of the quality of the signal reception of positioning. A minimum of four satellites are required to estimate the receiver's location and time [22]. The more satellites used, the greater the solution quality and integrity. This is an important estimator for these experiments because it helps to understand if the accuracy of a positioning augmentation system is getting affected by weather conditions or the satellites line of view, or the accuracy is just inferior. For these experiments, although the MADOCA positioning augmentation system registered on average more satellites than the CLAS, it performed worse. Therefore, the MADOCA inferior accuracy was not caused by the lack of satellites, it was caused by its inherent measurement principle. In addition, the RMSE was used to describe the accuracy by measuring the errors between each receiver position data and the actual position. As stated previously, the actual position was chosen as the mean position recorded by the receiver using RTK.