## 4 Results and Discussion
### Different Latitudes Area Results
#### 4.2.1 Low-Latitude Area Results  
In order to verify the results from the low-latitude area, the positioning accuracy and convergence time of SF PPP in static and dynamic modes during MS and NMS periods were analyzed.  
From Figure 6 in the kinematic mode, it can be seen that if the station was located in the low-latitude region, at the 95% level, TIC1 and TIC2 in the MS period and TIC1 in the NMS period did not converge. At the 68% level, the convergence time was longer than that of the stations distributed around the world. This may be due to fewer stations in the low-latitude area, which results in lower accuracy of the GIMs and the ZTD product, resulting in longer or no convergence time. In the static mode, although the convergence time was extended, it also converged, as shown in Figure 7.  
From analysis in Table 4, it can be seen that in the low-latitude region, the convergence time of TIC2 in the vertical component was shorter than that of TIC1 in the MS period, and also shorter than the convergence time of TIC1 in the NMS period. This showed that the tropospheric constraints in the low-latitude region contributed more to the convergence time in the vertical component. After the tropospheric constraint was added, the positioning accuracy was instantaneously below the threshold level of 68%, thereby achieving the effect of the convergence time being 0 min. However, the horizontal component convergence time was still the shortest in the NMS period, which was at least 11.0% shorter than TIC1.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scheme**} & \multicolumn{4}{c}{**Kinematic SF PPP (min)**} & \multicolumn{4}{c}{**Static SF PPP (min)**} \\ \cline{2-9}  & **H (95\%)** & **H (68\%)** & **V (95\%)** & **V (68\%)** & **H (95\%)** & **H (68\%)** & **V (95\%)** & **V (68\%)** \\ \hline TIC1\_MS & 150.5 & 57.0 & 156.5 & 0.0 & 53.5 & 28.5 & 47.0 & 0.0 \\ TIC2\_MS & 134.5 & 50.0 & 103.0 & 0.5 & 47.5 & 27.5 & 30.0 & 0.5 \\ TIC1\_NMS & 98.0 & 40.0 & 91.0 & 0.0 & 40.5 & 23.0 & 41.0 & 0.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The convergence times of GPS static and kinematic SF PPP in MS and NMS of TIC1 or TIC2.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scheme**} & \multicolumn{4}{c}{**Kinematic SF PPP (m)**} & \multicolumn{4}{c}{**Static SF PPP (m)**} \\ \cline{2-9}  & **H (95\%)** & **H (68\%)** & **V (95\%)** & **V (68\%)** & **H (95\%)** & **H (68\%)** & **V (95\%)** & **V (68\%)** \\ \hline TIC1\_MS & 0.475 & 0.204 & 0.474 & 0.083 & 0.205 & 0.085 & 0.182 & 0.035 \\ TIC2\_MS & 0.457 & 0.200 & 0.452 & 0.098 & 0.195 & 0.083 & 0.135 & 0.043 \\ TIC1\_NMS & 0.406 & 0.184 & 0.421 & 0.080 & 0.182 & 0.077 & 0.164 & 0.033 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The RMS of GPS static and kinematic SF PPP in MS and NMS of TIC1 or TIC2.  
Figure 6: The GPS kinematic SF PPP convergence performance in different constraint schemes during the MS and NMS periods.  
Figure 7: The GPS static SF PPP convergence performance in different constraint schemes during the MS and NMS periods.  
It was concluded in Table 5 that in the MS period of the low-latitude region, the RMS values of TIC2 and TIC1 were almost the same. For TIC1, the RMS value in the NMS period was smaller than that in the MS period, indicating that the MS had an influence on the positioning accuracy of the TIC1. The maximum RMS difference of TIC1 was 7.9 cm between the NMS period and the MS period. This result had a great influence on the positioning accuracy.