## 4 Evaluation of Dynamic Deformation Monitoring Using Smartphone  
The results reported above show that the RTK positioning accuracy of a smartphone can reach 1 cm, suggesting its potential for surveying and mapping applications. [PERSON] et al. [32] studied the feasibility of a low-cost u-blox receiver for dynamic deformation monitoring in high-rise buildings, and [PERSON] et al. [17] evaluated the static solution accuracy of smartphones in geodetic applications. Similarly, we explored the feasibility of using mass-produced smartphones as deformation monitoring devices through an experiment using simulated deformation equipment.  
As shown in Figure 14, the simulated deformation equipment can move along the east, north, and up directions and register the displacement. Before conducting the experiment, we calibrated the true north using a compass. A Xiaomi Mi 8 smartphone was then fixed on the simulation platform and its body was kept upright to ensure adequate signal reception.  
Figure 14: Experimental setup for simulated dynamic deformation monitoring.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Dataset**} & \multirow{2}{*}{**Segment**} & \multirow{2}{*}{**Convergence Time (min)**} & \multirow{2}{*}{**Mean Number of G/E Satellites**} & \multicolumn{2}{c}{**Mean Number of Candidate Ambiguities**} & \multirow{2}{*}{**Cycle-Slip Rate (\%)**} & \multirow{2}{*}{**Pseudo-Range RMS Residual (m)**} \\  & & & & & & \\ \hline \multirow{3}{*}{1} & 1 & 25.0 & 10.4 & 5.4 & 1.03 & 5.05 \\  & 2 & 12.8 & 10.9 & 7.7 & 0.12 & 4.37 \\  & 3 & 17.3 & 8.7 & 3.7 & 0.35 & 5.07 \\ \hline \multirow{3}{*}{2} & 1 & 13.0 & 11.2 & 8.0 & 0.37 & 5.87 \\  & 2 & 14.5 & 11.4 & 7.2 & 0.07 & 5.04 \\  & 3 & Not fixed & 11.1 & 0.4 & 0.35 & 5.28 \\ \hline \multirow{3}{*}{3} & 1 & Not fixed & 8.5 & 0.2 & 1.34 & 4.74 \\  & 2 & 33.9 & 8.2 & 4.0 & 0.17 & 4.66 \\ \cline{1-1}  & 3 & 13.3 & 9.3 & 7.2 & 0.31 & 4.60 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Statistical results of solutions per segment.  
During the experiment, the equipment was displaced once every 30 min to simulate the dynamic deformation of the monitored body. Considering the low accuracy of smartphone GNSS dynamic positioning, the horizontal displacement was set to 2 cm per movement. The schedule of the simulated deformation is listed in Table 9.  
For this experiment, we used GPS L1 observations to obtain the solutions, as there were few Galileo and BDS satellites in common view with the base station during the measurements. In addition, the ambiguity resolution mode was fix-and-hold. In the experiment, the average fixed solutions before the smartphone displaced in 1 h were used as the initial reference coordinates. The experimental results are shown in Figure 15. Centimetre-level accuracy is achieved as well as a fixing rate of 96.2%. In 9:00-9:30 and 9:30-10:00, the solutions suitably agree with the simulated deformation, and the deformation can be clearly seen at 9:00, 9:30, and 10:00. In the second half of the period 10:00-10:30 and the first half of the period 10:30-11:00, the solutions shift due to cycle slips, but they return to normal after some periods.  
The experimental results show that the deformation trend can be determined by using a smartphone, but owing to its high observation noise, deformation monitoring at the millimetre level cannot be achieved. In addition, a smartphone is extremely susceptible to interference from the environment and its own components during measurement. Consequently, it may not be applicable to actual monitoring scenarios at this stage of development. Improving the GNSS hardware quality in smartphones may enable monitoring applications in mass-produced smartphones.