## 4 Field Test Results and Discussions
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**St.** & **RTK (m)** & **SPP (m)** & **Fusion (m)** \\ \hline Daneshgah & 1.833 & 5.830 & 0.415 \\ Khorramshahr & 2.955 & 21.382 & 0.695 \\ Naderi & 16.356 & 10.759 & 2.445 \\ Peighambarieh & 5.425 & 8.830 & 1.515 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of the horizontal error of the positioning results with the S21 Ultra smartphone from the three SPP, RTK, and fusion methods with the U-Blox receiver. Figure 4: _Cont._  
Figure 4: GNSS raw observations processed by three methods, SPP, RTK, and fusion, respectively, on four streets, Daneshgah, Naderi, Peighambarieh, and Khorramshahr. The figures on the right (i.e., **b**,**d**,**f**,**h**) show the results of the Mi 8, and the figures on the left (i.e., **a**,**c**,**e**,**g**) show the results of the S21 Ultra. The next street is Naderi. Compared to the previous street, it contains relatively higher buildings while also being wider. By passing under a bridge located at an intersection, the route enters the street (Figure 3c), which may overshadow the satellite geometry. As can be seen, the SPP and RTK modes, specifically for the Samsung S21 Ultra phones, show a lower accuracy than the fusion method on Naderi Street compared to the same modes on Daneshgah Street. This fact also applies to the fusion method on both streets to a lesser extent. It can be inferred that the complex urban environment highly affected the positioning of Naderi Street in the SPP and RTK modes. The fusion method reduces the RMS value by 90%, decreasing from 15.638 m to 1.518 m, compared to the RTK mode for the Xiaomi Mi8 smartphone. Similarly, there is a decrease of 85% in the figure for the Samsung S21 Ultra, declining from 16.356 m to 2.445 m. Compared to the SPP mode, the RMS value calculated from the fusion method reduces by 75% for the Xiaomi Mi8 smartphone, decreasing from 6.240 m to 1.518 m. Following a similar pattern for the Samsung S21 Ultra, the fusion method shows a decrease of 77% in the RMS value relative to the SPP mode. The RMS value from the fusion method is around 2.445 m, while those for the SPP mode are about 10.759 m (Figure 6). Both phones exhibit the smallest error margins with the RTK mode, suggesting high-precision capabilities when the RTK mode is available. The SPP mode shows the most significant error margins for both devices, which is typical without the RTK mode or correction data. The error is more influential on Naderi Street than Daneshgah Street, potentially due to environmental challenges such as more significant urban canyon effects or signal obstructions. The fusion method demonstrates an improvement over the SPP mode for both devices, with the error margins notably closer to the RTK mode. This method's performance is consistent in both locations, suggesting robustness across different urban environments. Figure 5: Easting and Northing errors regarding the reference trajectory for the Samsung Ultra S21 (**a**,**c**), and Xiaomi Miß (**b**,**d**), on Daneshgah Street, respectively. The dotted line is the zero-error axis. As expected, the visible satellites are reduced while passing under the bridge, and this affects the accuracy of the positioning in the RTK RMS values, as shown in Figure 4c,d. The reason why the fusion method overcomes this problem is the integration of RTK observations with INS observations, and, in some cases, the replacement of RTK observations with INS observations. Accordingly, the role of this integration becomes more prominent when the number of visible satellites is inadequate and INS observations are more reliable than RTK ones. Peighambarieh Street is a narrow street with some high-rise buildings. The RMS values in RTK mode for the Xiaomi Mi8 and Samsung S21 Ultra are around 9.805 m and 5.425 m, which, with the fusion method, decreased to 1.188 m and 1.515 m, respectively. These reductions of 88% and 72% are achieved by utilizing the fusion method instead of the RTK mode.