## 3 Results and Discussion
### Variation in Overlap and Height  
Figure 8 shows the values and behavior of the depth measurement error when varying height and overlap in vertical photo acquisition flights (90-degree camera angle) for different severity of potholes (low severity in Figure 8a, middle severity in Figure 8b and high severity in Figure 8c). Figure 8: _Cont._  
According to Figure 8a, it is observed that the error trend of all overlaps increases as the measurement height grows, which makes sense as the resolution of the photograph (GSD) decreases. In addition, the error variation decreases as the measurement height increases, indicating that errors converge due to their null interpretation, since the 100% error indicates that the variable to be measured in the model is not identified. On the other hand, there is no optimal overlap that applies to all of the heights. For 2 m, the best result was obtained for an overlap of 75%, with an error of 8.8%. For 5 m, the lowest error was 21.3% for a 90% overlap. For 8 m, the 85% overlap achieved the best results, resulting in an error of 37.1%. At 10 m, the minimum error was 57.7%, which is associated with an overlap of 80%, this error is 1.3% lower compared to an overlap of 75%, even more the error is reduced by more than 15% compared to overlaps of 85 and 90%. While, at 15 m, the 90% overlap has the lowest error (89.4%), an error that is 0.5% less compared to an overlap of 85%; moreover, the error is reduced by more than 5% compared to overlaps of 75 and 80%. However, the error is high (+89%). At 20 m, the least error (93.5%) was obtained with an overlap of 90%, the other overlaps had an error between 93.8-98.8%. At 25 m, there is a 100% error for the overlap of 80%, indicating that no depth could be measured for any of the potholes analyzed, while for overlaps of 75 and 90% the error is 87.5% for both and, for the overlap of 85%, an error of 98.8% was obtained. At 30 m, the overlaps of 80, 85 and 90% obtained a 100% error, which as stated above indicates that no depth was measured. Additionally, with the overlap of 75%, a 98.8% error was obtained, indicating that it was measured because the reconstruction of the 3D model created a slope in a pothole. At 40 m, all overlaps get an error of 100%, that is, no elevation was appreciated in the model; for this reason, the interpretation of the potholes in the model is like that of a circular horizontal dark spot. It can be observed that from 15 m that the error is high (about 90%) for the various overlaps, indicating that the analysis for higher heights is no longer representative for this type of measurement. However, it noted that the simulated potholes analyzed in the experiment would not present the same conditions in practice. In other words, since the experiment considers the value of width as twice the depth, due to its semi-spherical shape, it makes it a more conservative analysis, since the width of a pothole is much greater than its depth. Figure 8: Average relative depth error behavior for different severity levels when varying overlap and height for vertical image acquisition (90\({}^{\circ}\)). (**a**) Low severity; (**b**) mean severity; (**c**) high severity. From Figure 8b, an optimal overlap is clearly observed for the heights of 2, 5, 8, 15, 20, 25 and 30 m, while, for the heights of 10 and 40 m, its optimum is not apparent at first sight. At 2 m, the least error was obtained (4%), four with an overlap of 85%; the other overlaps (75, 85 and 90%) have an error difference that exceeds 0.6% compared to the overlap of 75%. At 5 m, the optimal overlap is 85%, because with this overlap and height, the error is the lowest, specifically 2.3%; this error is 2.3% lower compared to an overlap of 90%. At 15 m, the least error was obtained (30.2%) with an overlap of 80%, the other overlaps (75, 85 and 90%) have an error difference that exceeds 22% compared to the overlap of 80%. At 8 m and 80% overlap, a 6% error was obtained, which is the lowest--5.9% lower compared to the 75% overlap.