## 3 Results and Discussion  
### Vertical Displacements  
For the investigation of uplift cases, eight paving blocks were lifted by 5, 7.5, and 10 mm. As shown in Figures 7-9, it was possible to detect every tested uplift case. Note that blue indicates no displacement and green indicates displacement. The number of subset points where displacements occurred was approximately between 25,000 and 30,000. As indicated in the subfigures (d) of Figures 7-9, it can be seen that the distribution of displacements appears close to the normal distribution. When the accuracy was evaluated  
Figure 6: Reference set up for paving blocks for the detection and measurement of block displacements. by subtracting the actual uplift value from the mean value (\(\upmu\)) measured by the PCD, the tested cases of 5, 7.5, and 10 mm were 0.241, 0.074, and 0.080 mm, respectively. Herein, the standard deviation (\(\sigma\)) of the PCD measurements was regarded as precision. The precisions for the tested cases of 5, 7.5, and 10 mm were 0.930, 0.939, and 1.003 mm, respectively. To investigate the settlement of the paving blocks, eight paving blocks were set to 5, 7.5, and 10 mm. As displayed in Figures 10-12, it is possible to detect every tested case. Since the C2C algorithm calculates the distance to the nearest point between PCD, information about directionality, such as settlement and uplift, is unknown. Similar to the  
Figure 8: PCD of 7.5 mm uplift: (**a**) PCD; (**b**) visualization of the uplifted zone; (**c**) zoomed in the 7.5 mm uplifted zone; (**d**) histogram of the uplifted zone. Figure 7: PCD of 5.0 mm uplift: (**a**) PCD; (**b**) visualization of the uplifted zone; (**c**) zoomed in the 5.0 mm uplifted zone; (**d**) histogram of the uplifted zone. Figure 9: PCD of 10.0 mm uplift: (**a**) PCD; (**b**) visualization of the uplifted zone; (**c**) zoomed in the 10 mm uplifted zone; (**d**) histogram of the uplifted zone. investigated uplift cases, blue indicates no displacement, and green indicates displacement. The number of subset points where displacements occurred was approximately between 25,000 and 30,000. As shown in the histogram of each case, the distribution was close to the normal distribution like the uplift cases. The mean values of the PCD measurements for the three cases were 5.881, 7.468, and 9.876 mm, respectively. When the accuracies were evaluated as in the uplift cases, the accuracies of the 5, 7.5, and 10 mm cases were 0.881, 0.032, and 0.024 mm, respectively. In addition, the standard deviations of three cases were 1.672, 1.231, and 1.445 mm for cases of 5, 7.5, and 10 mm, respectively. Figure 11: PCD of the 7.5 mm settlement: (**a**) PCD; (**b**) settled zone visualization; (**c**) zoomed in the 7.5 mm settled zone; (**d**) histogram of the settled zone. Figure 12: PCD of the 10.0 mm settlement: (**a**) PCD; (**b**) settled zone visualization; (**c**) zoomed in the 10.0 mm settled zone; (**d**) histogram of the settled zone. Figure 10: PCD of the 5.0 mm settlement: (**a**) PCD; (**b**) settled zone visualization; (**c**) zoomed in the 5.0 mm settled zone; (**d**) histogram of the settled zone. Conventionally, the vertical displacement is evaluated by the level instrument at the installed settlement point; therefore, information about only that point can be obtained. However, the advantage of the level instrument is that it can measure a vertical displacement of 5 mm or less, which has not been tested here. Note that the standard deviation for the 1 km double-run levelling of these instruments is approximately 1 or 2 mm, as evaluated by ISO 17123-2 [38]. Based on the cases investigated using terrestrial photogrammetry, it can be inferred that it was possible to detect a vertical displacement of more than 5 mm. Vertical displacement evaluation using PCD is a measurement of a surface, and not a single point. Accordingly, it has the advantage of being able to determine displacements that would not have been known if there were no settlement points for the level instrument.