# UAV Application for Typhoon Damage Assessment in Construction Sites
## 5 Discussion  
According to the investigation and assessment of the risk before natural disasters, it was found that the impact of natural disasters on the construction site was caused by  
Figure 11: Corrosion and loosening. Figure 12: Derailment of wire rope. multiple factors and multiple nodes. For example, a typhoon disaster will blow down the tower crane, whose crane will further lead to the destruction of construction progress or squash other large machinery. It may stop at this point in the disaster timeline or continue to create a chain of disasters. Through case demonstration, it is not difficult to find that if we can take measures in the first part of the typhoon's impact on the tower crane, we can significantly reduce the possibility of the subsequent disaster, which is the \"broken chain\" theory to be researched in this paper. Relevant theoretical studies are shown in Table 10.  
Table 10 divides the occurrence of the disaster chain into three links, including propphase, metaphase, and anaphase. Since the impact of the typhoon on construction sites is unique, we combined its characteristics and disaster chain theory in making warning processes and measures for disaster prevention and mitigation. The warning flow is shown in Figure 13. After the weather bureau releases the weather information in advance, we judged the level of natural disaster information. If the risk of typhoon is too low, no warning is given. If the natural disaster is between I and IV, the corresponding disaster prevention and mitigation measures are given. The disaster prevention and mitigation measures are based on the quantitative calculation results of AHP. It can be seen from the calculated data that among the five factors, risk factors account for 39.02%, and disaster prevention index factors account for 25.24%, indicating that we should invest more resources in disaster prevention and mitigation. In this way, disaster prevention resources can be maximized. In the same way, in the sub-indices of these five factors, such as the indicator of disaster prevention capability, we can obtain that the meteorological bureau's prediction accuracy of disasters, the strength of construction safety emergency personnel, and the level of construction safety emergency equipment account for a relatively large proportion. Therefore, we must ensure the accuracy of the disaster level of early warning and carry out targeted prevention during disaster prevention. In addition, we should pay attention to the construction of disaster prevention teams and improve the management level of disaster prevention managers during disaster prevention, use advanced technology to prevent and reduce disasters, and further demonstrate that it is very necessary to use drones to prevent and reduce disasters on construction sites. According to the judgment results of different typhoon levels, we developed detailed measures shown in Table 11.  
The application of UAV photography technology in the construction site was verified through the case of Xiamen Electronic City. On the one hand, it used the site photo data obtained by UAV and then used modeling software (smart3D and pix4d mapper) for 3D modeling analysis. On the other hand, 2D image processing and analysis were carried out using the photo data obtained by the UAV. First of all, the single model built by the modeling software (especially the use of smart3D) can reflect every detail of the building with high precision and can provide construction managers with a 360\({}^{\circ}\) inspection without dead ends. A short buffer time before a disaster strikes and resources are allocated for defense. For example, if those important construction materials have not been transferred, you can know immediately. In addition, the establishment of the 3D model can be established before and after the disaster, which is conducive to the comparison before and after the disaster, so that the loss can be determined as soon as possible, and a data account can