## 3 Experimental Results  
### Data Acquisition  
In this experiment, a Laser Pointer model was developed that can be attached to an unmanned aerial vehicle's camera sensor. Aerial photography was conducted on the exterior wall of a concrete building located in Buk-gu, Daegu, Republic of Korea. In the case of the exterior wall of the building selected as the test subject, there is a feature object that can be defined as a reference object, but there are no surrounding obstacles during aerial photography, and there are parts that are judged to have insufficient feature points on the exterior wall of the building. Therefore, an experiment was conducted by selecting a target for the methodology presented in this study. The overview of the target area where aerial photography was performed in this study is shown in Figure 2.  
UAV and camera sensor used in this study are the Inspire 2 and Zenmuse X5S models from DJI in Shenzhen, China. The upward infrared sensor can detect surrounding obstacles up to 5 m, the downward vision system ranges from 0.1 to 5 m, and the forward vision system operates between 0.7 to 30 m. The Field of View (FOV) can identify objects within a horizontal range of 60\({}^{\circ}\) and a vertical range of 54\({}^{\circ}\). The camera lens has a focal length of 15 mm, and the image sensor size is 17.3 mm \(\times\) 9.7 mm for CMOS 4/3\({}^{\prime\prime}\). The resolution is 5280 \(\times\) 2970 with a 16:9 aspect ratio, allowing for capturing photos with a maximum resolution of 20.8 MP. Additionally, the Laser Pointer model developed for mounting on the camera sensor was designed and manufactured using a 3D printer, as shown in Figure 3.  
For the flight path, the exterior wall of the target building was planned in a single grid format, and the angle of the exterior wall of the building and the camera sensor were set vertically. The UAV shooting path planned in this study is shown in Figure 4.  
Figure 2: Overview of the target site.  
The aerial photography was conducted on 6 May 2023, based on the flight plan prepared in advance. The photography was carried out using manual flight control, considering the positioning of the Laser Pointer model-equipped UAV in relation to the exterior wall of the building. During a total flight time of 10 min, 107 images were acquired with the following camera settings: ISO--100, Aperture--F/2, Shutter speed--1/120 s, and Shooting angle--0\({}^{\circ}\). The distance between the UAV and the target building's exterior wall was set to approximately 2 m, considering the projection and position estimation of the Laser Pointer. While obtaining aerial photographs with uniform image overlap using manual flight control can be challenging, a minimum of 65% image overlap was achieved among the acquired aerial photographs.  
Figure 4: UAV shooting path plan.  
Figure 3: Laser Pointer model and mounting on the camera sensor.  
The analysis of the aerial images from the aerial photography revealed a clear identification of the cracks in the building and the Laser Point. Based on this, the study utilized the aerial images with the displayed Laser Point to construct spatial information using image processing techniques aimed at the localization of concrete cracks.