# Utilization of Quasi-Zenith Satellite System for Navigation of a Robot Combine Harvester
## 3 Results
### Performance Evaluation of Robot Combine Harvester  
By utilizing the CLAS and MADOCA for navigation of the robot combine harvester, it was verified that the robot combine could perform automatic operation along four paths of the predesigned navigation map, as shown in Figure 8. In Figure 8, the predesigned navigation map is represented by the dashed line. The solid dark line in Figure 8 represents the CLAS traveled path, and in Figure 8 the solid dark line represents the MADOCA traveled path. Each run took about 20 min. However, it might be difficult to specify the accuracy of each positioning augmentation system for the robot combine harvester navigation. Therefore, further performance evaluation of the experiment is necessary; as described below. Table 4 summarizes the results from the performance evaluation of a robot combine harvester experiments. The lateral deviation was calculated by the comparison between the predesigned navigation map and the logged position data from the RTK, the CLAS and the MADOCA. Please remember that the straight path contained in the navigation map serves as the target position, and the position points logged by each different positioning augmentation system will have some lateral deviation from this target position. The RMSE of this lateral deviation is calculated using Equation (3). In this experiment, four runs were performed at two-hour intervals. Each experimental run took about 10 min. The comparison between the RMSE of lateral deviation from the four runs shows that the RTK and the CLAS are stable, it is possible to state that for the dynamic experiment CLAS might be as good as RTK because it displays a RMSE less than 0.06 m.  
Figure 8: Logged positioning data of the robot combine harvester (**a**) CLAS, (**b**) MADOCA. Figure 7: Logged positioning data for six hours from the static positioning experiment (**a**) CLAS, (**b**) MADOCA. Figure 9 shows the logged position data from the first runs by using the CLAS and MADOCA to control the robot combine harvester. The dashed line represents the positioning augmentation system used at each experimental run. The solid clear line at the zero of the vertical axis represents the map points followed by the automatic controller of the robot combine harvester. The solid dark line represents the RTK data used as a reference. Table 5 summarizes the results from the robot combine harvest controlled by CLAS under the dynamic conditions. The difference of the RMSE of the lateral deviation between the CLAS and the RTK is almost constant since the time the experiment started; which means the position data provided by the CLAS always converge to the position data provided by the RTK during the six hours of the experiment. Therefore, the CLAS does not has the time dependency phenomenon. The average RMSE of the lateral deviation of the RTK or actual path is 0.09 m and 0.23 m for the first path and second path, respectively. It is necessary to consider that when the robot combine harvester performs a round trip, the width of the header used for harvesting requires a minimum distance between the going and the returning path. If this distance is too big, it might result in a gap of unharvested plants between the going and the returning path. This distance is defined as the overlap of the robot combine harvester. Due to these RMSE values, the overlap between each path of the predesigned navigation map should be set to 0.09 m while using the CLAS to control the robot combine harvester. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Positioning Augmentation System**} & \multicolumn{4}{c}{**RMSE of Lateral Deviation (m)**} \\ \cline{2-5}  & **1 st Run at 10:00** & **2 nd Run at 12:00** & **3 rd Run at 14:00** & **4 th Run at 16:00** \\ \hline RTK & 0.04 & 0.03 & 0.04 & 0.03 \\ MADOCA & 0.32 & 0.18 & 0.06 & 0.07 \\ CLAS & 0.06 & 0.05 & 0.04 & 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results from dynamic positioning experiments controlled by RTK.