# Application of Multi-System Combination Precise Point Positioning in Landslide Monitoring
## 5 Application of Multi-System Combination PPP in Landslide Monitoring
### Analysis of Positioning Accuracy  
To further verify the reliability of the calculating results, continuous reference stations were set up at the stable points outside the landslide disaster area for static synchronous observation. The calculation coordinates of 24 h static synchronous observation data between the reference point and the monitoring point were taken as the initial coordinates of the monitoring point. The HCMonitor software provided by Huace Navigation was used to calculate the static relative positioning. Figure 10 shows the cumulative changes of the static relative positioning of the monitoring points in the north (N), east (E) and elevation (U) directions. According to the analysis of Figure 10, the cumulative displacement of the monitoring point data in the observation period in the N direction is 9.54 mm, the cumulative displacement in the E direction is 7.38 mm, and in the U direction, it is 19.2 mm. During the observation period, the horizontal displacement of the monitoring point moved along the N and E directions, with the trend of slightly sinking in the elevation direction. The static relative positioning results can identify the millimeter-scale landslide shape variables, which provides a reliable external verification means for PPP results.  
Figure 9: The deviation of splicing solution.  
Figure 11 shows the difference between the three directions of ENU solution results in G/R/C, G/R/E and G/R/E/C combined PPP and the static relative positioning solution results in the observation period. Through the analysis of Figure 11, it can be seen that the maximum deviation of the G/R/C combination PPP and static relative positioning calculation results in the three directions of NEU are 1.28, 2.82 and 4.90 cm, the minimum deviation is 0.01, 0.02 and 0.05 cm, and the average deviation is 0.49, 1.43 and 2.43 cm. The maximum deviation of G/R/E combination PPP and static relative positioning in three directions of NEU is 2.74, 1.31 and 4.94 cm, the minimum deviation is 0.01, 0.12 and 0.03 cm, and the average deviation is 0.51, 1.45 and 2.48 cm. The maximum deviation of the G/R/E/C combination PPP and static relative positioning results in the three directions of NEU is 1.49, 2.97 and 4.89 cm, and the minimum deviation is 0.01, 0.02 and 0.05 cm, respectively. The mean deviation is 0.49, 1.42 and 2.43 cm. To more intuitively compare the difference between the results of multi-system combination PPP and the static relative positioning solution, Table 1 quantifies the difference between the results of the PPP solution and the static relative positioning solution in the three directions of NEU at an interval of one month. To sum up, the accuracy of the calculation results of G/R/C, G/R/E and G/R/E/C combined PPP is basically the same, and the external coincidence accuracy is better than 5 cm for all solutions, so they can be applied to the landslide monitoring of centimeter-level slope movement.  
Figure 10: Cumulative shape variables of monitoring points.  
Figure 11: Comparison of difference between combined PPP and static relative positioning results.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Combination**} & \multirow{2}{*}{**Date**} & \multicolumn{3}{c}{**Deviation/cm**} & \multicolumn{3}{c}{**RMSE**} \\ \cline{3-8}  & **(Year/Month/Day)** & **E** & **N** & **U** & **E** & **N** & **U** \\ \hline \multirow{9}{*}{G/R/C} & 2019/6/18 & 0.79 & 0.69 & 3.37 & 1.32 & 0.55 & 2.85 \\  & 2019