# UAV Application for Typhoon Damage Assessment in Construction Sites
## 4 Case Study and Process Design
### Monomer Modeling  
According to the pix4d 3D modeling results, although the established 3D model of the construction site can visually observe the entire layout of the site, the accuracy of the details is low, which is not conducive to the development of site risk investigation. However, Smart3D software can carry out some point cloud models, monomers, and visual data. Due to the limitation, the output model of UAV oblique photography automatic modeling is an overall model, which cannot be implemented for selecting specific building objects and querying spatial information and other attribute information. We needed to monetize the model so that the data could be managed, not just viewed. Monomer modeling is to assign a single attribute to a single model in the model scene so that it can be observed and managed separately. The risk management of the construction site needs to check the various facilities on the construction site one by one, so individual modeling is an effective tool for project managers to carry out risk management. In this study, the slanted model was cut and singulated according to the needs of model management and the structure of the building itself so as to separate it from the physical structure and achieve singulation.  
The first was the establishment of the model scene. The 3D model was constructed by the Context Capture modeling software, and the spatial data were loaded. The coordinate system of the model itself adopted the World Geodetic System (WGS84) geographic coordinate system. The model had not only high-precision geographic latitude and longitude coordinates but also had precise elevation coordinates. The case of the Xiamen campus of Huaqiao University was taken as an example of building a 3D model. Figure 8 shows the building process of the library's 3D point cloud model. Firstly, point cloud registration and noise filtering were performed, then point cloud classification was performed, and finally, point cloud model rendering was performed. The final 3D model was not much different from the actual building, so the model establishment had high accuracy.  
Figure 8: Building process of the library’s 3D point cloud model.  
Then, the monomer was modeled. The singulation is to use the vector surfaces corresponding to the buildings, roads, trees, etc., in the built 3D model to cut the oblique photographic model. Considering that the study used UAV photography for construction site risk visualization management, the method of dynamic vector surface superposition was used based on the system platform to achieve model singulation. The matching 2D vector faces were loaded into the same scene as the oblique photographic model. When rendering model data, the vector surface was stuck to the surface of the inclined model object, and then the color and transparency of the vector surface were set to achieve the effect that the features can be individually selected. The Smart3D Viewer module was used to collect two-dimensional vector coordinates for the single building to be realized. Through Polygon Hierarchy, the collected coordinates were used to construct the vector polygon to complete the geometry. For model transparency, highlighting was performed by adjusting material and classification type.  
Rapidity and accuracy are advantages in earthmoving measurement by the 3D model, compared with the traditional earthmoving technology. Figure 9 shows a volume measurement using smart3D software. The left property bar shows the values of \"cut/fill\", \"fill\", and \"sampling distance\", which corresponds to the amount of \"net cut/fill\", \"fill\", and \"cut\". The traditional earthwork method has a large amount of calculation, low precision, and low efficiency. However, the foundation pit collapse caused by heavy rain and flood on the construction site needs to be dealt with as soon as possible. The use of 3D modeling software, with the broad prospect of use, can realize fast and accurate calculations to solve the problem of safety inspection before a natural disaster.