# An In-Vehicle Smartphone RTK/DR Positioning Method Combined with OSM Road Network
## 3 Results
### Statistics and Analysis of Smartphone Positioning Error
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Test** \\ **Number** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Heading Angle Error** \\ **RMS (Degrees)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Accuracy** \\ **Change** \\ \end{tabular} } & \multicolumn{2}{c}{\
\begin{tabular}{c} **Velocity Error** \\ **RMS (m/s)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Accuracy** \\ **Change** \\ \end{tabular} } \\ \cline{2-2} \cline{4-6}  & **RTK** & & & **RTK** & & **RTK/DR** \\ \hline P30-1 & 2.392 & 2.215 & 7.4\% & 2.804 & 2.813 & \(-\)0.3\% \\ P30-2 & 2.334 & 2.103 & 9.9\% & 0.242 & 0.245 & \(-\)1.1\% \\ P30-3 & 2.897 & 2.081 & 28.2\% & 0.804 & 0.805 & \(-\)0.7\% \\ P30-4 & 2.353 & 1.629 & 30.8\% & 0.313 & 0.314 & \(-\)0.2\% \\ P40-1 & 2.820 & 2.346 & 16.8\% & 2.743 & 2.745 & \(-\)0.1\% \\ P40-2 & 2.896 & 2.293 & 20.8\% & 0.276 & 0.263 & 4.7\% \\ P40-3 & 2.977 & 1.808 & 39.3\% & 0.502 & 0.499 & 0.7\% \\ P40-4 & 2.195 & 1.539 & 29.9\% & 0.255 & 0.255 & 0.0\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Statistics of heading angle and velocity error achieved by using RTK/DR positioning method. Figure 10: RTK/DR positioning track. (**a**) Smartphone Huawei P30; (**b**) Smartphone Huawei P40. RTK lateral error RMS is higher than the forward error RMS, indicating that there are many lateral drifts and jumps in the positioning results, due mainly to the environment on both road sides. In the eight sets of test results, the RMS fluctuation of the smartphone RTK positioning horizontal positioning error is significant, the minimum value is 1.065 m, and the maximum value is 2.343 m.  
Compared with the RTK results, RTK/DR achieves significant performance differences, in terms of lateral and forward error. The lateral accuracy of RTK/DR is better than that of RTK. The lateral accuracy of P30 is improved by 10%, while the lateral accuracy of P40 is improved by more than 20%. The forward accuracy of RTK/DR slightly decreases, and the decrease achieved by using both smartphones is within 1%. The horizontal accuracy of RTK/DR is better than RTK in each set of tests. P30 has only a tiny improvement of 2-5%, while P40 has a 10-30% improvement. The four times of vehicle positioning results were merged, so that they were displayed according to the smartphone model, as shown in Figure 11 and Table 4. It can be seen that the lateral error of RTK/DR is significantly lower than that of RTK, while the error fluctuation is slight. However, the forward error distributions of RTK/DR and RTK are highly consistent, so the difference between the two positioning methods cannot be identified. The horizontal error RMS of the two smartphones is almost identical, i.e., lower than 1.3 m. Compared with the RTK results, the RTK/DR horizontal accuracy of the P30 is improved by 5.9%, while the RTK/DR horizontal accuracy of the P40 is improved by 44.4%. Combined with the error analysis of the heading angle and velocity, it can be deduced that the heading angle affects mainly the lateral positioning accuracy, so the accuracy improvement of the heading angle promotes the improvement of the lateral accuracy. The velocity mainly affects the forward positioning accuracy. According to the calculation formula of velocity, the velocity noise of RTK/DR includes the velocity noise of RTK and the heading angle noise of DR, so that the forward accuracy of RTK/DR is lower than that of RTK. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Smarthphone Model**} & \multicolumn{3}{c}{**RTK (m)**} & \multicolumn{3}{c}{**RTK/DR (m)**} \\ \cline{2-7}  & **Lateral** & **Forward** & **Horizontal** & **Lateral** & **Forward** & **Horizontal** \\ \hline P30 & 1.012 & 0.852 & 1.323 & 0.902 & 0.859 & 1.245 \\ P40 & 2.042 & 1.016 & 2.281 & 0.742 & 1.027 & 1.267 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistics of positioning error RMS of Smartphones Huawei P30 and P40.