# 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 c c c} \hline \hline \multirow{2}{*}{**Test**} & \multicolumn{3}{c}{**RTK (m)**} & \multicolumn{3}{c}{**RTK/DR (m)**} & \multicolumn{3}{c}{**RTK/DR Accuracy Variation**} \\ \cline{2-10}  & **Lateral** & **Forward** & **Horizontal** & **Lateral** & **Forward** & **Horizontal** & **Lateral** & **Forward** & **Horizontal** \\ \hline P30-1 & 1.166 & 1.122 & 1.619 & 1.049 & 1.129 & 1.542 & 10.0\% & \(-\)0.6\% & 4.7\% \\ P30-2 & 0.834 & 0.742 & 1.116 & 0.768 & 0.745 & 1.070 & 7.9\% & \(-\)0.5\% & 4.1\% \\ P30-3 & 1.041 & 0.868 & 1.356 & 0.990 & 0.871 & 1.319 & 4.9\% & \(-\)0.3\% & 2.7\% \\ P30-4 & 0.957 & 0.934 & 1.337 & 0.908 & 0.935 & 1.304 & 5.0\% & \(-\)0.1\% & 2.5\% \\ P40-1 & 1.732 & 1.121 & 2.063 & 1.066 & 1.131 & 1.554 & 38.4\% & \(-\)0.8\% & 24.6\% \\ P40-2 & 0.888 & 0.618 & 1.082 & 0.692 & 0.623 & 0.931 & 22.0\% & \(-\)0.8\% & 13.9\% \\ P40-3 & 1.852 & 1.435 & 2.343 & 0.910 & 1.440 & 1.704 & 50.8\% & \(-\)0.4\% & 27.3\% \\ P40-4 & 0.926 & 0.526 & 1.065 & 0.724 & 0.529 & 0.896 & 21.8\% & \(-\)0.5\% & 15.8\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistics of positioning error RMS. Smartphone horizontal positioning accuracy is also affected by the measurement update switch. When RTK sharply jumps, if the measurement update is not turned off in time, RTK/DR will carry the RTK positioning error of the previous epoch, resulting in error accumulation. Table 5 shows the number of epochs in which the measurement update is turned off in the eight sets of tests. Although the driving routes of the vehicle are the same, the number of stop measurement updates in each group of tests is quite different. Among them, the number of stop measurement updates for P40-1 and P40-2 reaches more than 400 times, accounting for more than 35%. There are a total of 8851 epochs of positioning results, of which 2534 epochs automatically stop the measurement update, accounting for 28.6%. As far as the results of horizontal position accuracy in Tables 3 and 5, the horizontal position accuracy of RTK during the closed measurement update period is lower than the overall accuracy, which shows that the measurement update switch can effectively identify the period with significant RTK error. In addition, the positioning accuracy of DR in each group of tests is higher than that of RTK, which shows that DR can maintain reliable positioning when RTK positioning results are not good. Figure 11 shows that the error fluctuation of the RTK positioning results of P40 is more severe than that of P30. Therefore, the number of measurement update stops for P40 is higher than that for P30 in each test. Ultimately, the positioning accuracy difference between RTK/DR and RTK of P40 is more significant than that of P30. Figure 11: RTK/DR positioning error along lateral and forward direction. (**a**) Smartphone Huawei P30; (**b**) Smartphone Huawei P40. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test** & **Total Number** & **Number of** & \multicolumn{2}{c}{**Horizontal Position Accuracy**} \\ \cline{3-5}
**Number** & **of Epochs** & **Stop Epochs** & **DR** & **RTK/DR** \\ \hline P30-1 & 1111 & 255 & 1.739 & 2.017 \\ P30-2 & 1194 & 203 & 1.216 & 1.382 \\ P30-3 & 1170 & 332 & 1.669 & 1.673 \\ P30-4 & 984 & 221 & 1.725 & 1.773 \\ P40-1 & 1073 & 428 & 1.619 & 2.737 \\ P40-2 & 1179 & 436 & 1.093 & 1.455 \\ P40-3 & 1160 & 390 & 2.630 & 3.817 \\ P40-4 & 980 & 269 & 1.063 & 1.496 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Number of epochs for stop of measurement updates.