## 4 Analysis of Bridge Deformation Characteristics
### Dynamic Deformation Characteristics of the Fenghuangshan Road Bridge Based on GB-RAR Technology
#### 4.2.1 Remote Monitoring of Close-Range Photogrammetry Technology  
To verify the feasibility of the remote monitoring of bridge dynamic deformation based on the isometric virtual plane digital photography technique, this study evaluates the measurement accuracy before the bridge deformation monitoring experiment. The details are as follows:  
* Install a prism and monitored signs in a stable area; thus, the prism is in the same position as the monitored signs, which is convenient for the accurate measurement of the actual distance of monitored signs from the monitoring device.
* Along the vertical line, utilize technology equipment pertaining to the remote monitoring of close-range photogrammetry. Thus, signs 250 m, 225 m, 200 m, 175 m, and 150 m away are monitored to obtain corresponding high-quality photos (Figure 24).
* After obtaining an external image, utilize dynamic data processing software to add control points and monitoring points. Data processing is performed using the time  
Figure 23: The overall deformation of the bridge at different times with a 100 Hz sampling frequency.  
Figure 22: The overall deformation of the bridge at different times with a 100 Hz sampling frequency.  
difference method based on the time baseline, and a photography scale at different monitoring distances is obtained (Table 1).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Monitoring Distance/m** & **DX0** & **DX20** & **Scale Coefficient M** \\ \hline \multirow{4}{*}{250} & \(-27.18\) & \(81.19\) & \(1.12\) \\  & \(-54.94\) & \(163.75\) & \(1.12\) \\  & \(-83.1\) & \(252.1\) & \(1.12\) \\  & \(-109.01\) & \(330.85\) & \(1.13\) \\ \hline \multirow{4}{*}{225} & \(-27.34\) & \(87.61\) & \(1.01\) \\  & \(-55.88\) & \(180.98\) & \(1.02\) \\  & \(-83.28\) & \(274.42\) & \(1.01\) \\  & \(-110.36\) & \(364.51\) & \(1.03\) \\ \hline \multirow{4}{*}{200} & \(-11.16\) & \(104.23\) & \(0.89\) \\  & \(-22.76\) & \(216.12\) & \(0.89\) \\  & \(-33.53\) & \(332.91\) & \(0.91\) \\  & \(-44.96\) & \(441.04\) & \(0.91\) \\ \hline \multirow{4}{*}{175} & \(-33.84\) & \(124.19\) & \(0.76\) \\  & \(-68.08\) & \(249.96\) & \(0.76\) \\  & \(-101.59\) & \(378.17\) & \(0.77\) \\  & \(-134.4\) & \(496.57\) & \(0.76\) \\ \hline \multirow{4}{*}{150} & \(-43.68\) & \(138.05\) & \(0.67\) \\  & \(-89.11\) & \(288.25\) & \(0.66\) \\ \cline{1-1}  & \(-132.17\) & \(428.06\) & \(0.67\) \\ \cline{1-1}  & \(-174.38\) & \(562.61\) & \(0.67\) \\ \hline \end{tabular}
\end{table}
Table 1: Pixel correction table at different distances.  
Figure 24: Assessment diagram of over-the-horizon accuracy. (**a**) A 250 m photographic distance; (**b**) 225 m photographic distance; (**c**) 200 m photographic distance; (**d**) 175 m photographic distance; (**e**) 150 m photographic distance; (**f**) observer.  
After data processing, it is observed that when the monitoring distance is 150 m, the photography scale is approximately 0.66 mm/pixel. When the monitoring distance is 175 m, the photographic scale is approximately 0.76 mm/pixel; when the monitoring distance is 200 m, the photographic scale is approximately 0.90 mm/pixel; when the monitoring distance is 225 m, the photographic scale is approximately 1.02 mm/pixel; and when the monitoring distance is 250 m, the photographic scale is approximately 1.12 mm/pixel. According to the close-range photogrammetry experiment, measurement technology equipment pertaining to the remote monitoring of close-range photogrammetry was utilized at 250 m, 225 m, 200 m, 175 m, and 150 m, which can be equivalent to the close-range photogrammetry technology at 8 m, 6 m, 4 m, and 2 m, respectively, with a mean square error of approximately 0.5 pixels. Therefore, it can be considered that the remote monitoring of bridge dynamic deformation using digital photography technology based on the isometric virtual plane can meet the accuracy requirements of the deformation monitoring experiment and is feasible.