## 2 System Architecture
### Drone Three-Dimensional Coordinate Calculation  
(1) Detection method for drone height: The rotation direction and angle judgment mode of the dual-axis tracing device are based on the value sensed from nine-axis attitude meters. Therefore, there is a close relationship between the placement position of the attitude meter and the accuracy of the system data. The starting point of orientation determination by an attitude sensing component is based on the preset position of its own module. The drone movement orientation of the screen image is based on the movement of the lens, so the position of the sensing component of the attitude meter should be placed as close as possible to the camera lens, so that the angular deviation will be smaller. After many tests, we found that it has the best effect when placed under the lens. When the tracing device finds that the drone has entered the visual image of the screen as in Figure 6, the system immediately traces the drone image in the screen through visual identification, and computes the relative relationship between the drone image and the center point of the visual image screen. Then, it performs an action of target drone tracing and position locking. The drone image enters the center point \((x_{1},y_{1})\) of the visual image screen of the tracing device, and the laser ranger can measure when the target drone enters the laser ranging range. The distance value (\(r\)) from the target is obtained, and the pitch angle (\(\theta\)) of the rotating stage at this time is obtained by the nine-axis attitude meter in the apparatus. As shown in Equation (7), the flight altitude h of the drone can be converted. \[h=r\times sin\theta=\sqrt{\left(x_{2}-x_{1}\right)^{2}+\left(y_{2}-y_{1} \right)^{2}}\times sin\theta \tag{8}\]  
Figure 5: Schematic diagram of the relationship between the step angle and image. (2) Detection method for drone longitude and latitude coordinate as well as azimuth: When the tracing system locks the target drone to the center point position \((x_{1},y_{1})\) of the image screen through tracing, the target drone has entered the laser ranging range. The values of the distance and the horizontal elevation angle of the target drone from the test site can be obtained by laser rangers and the attitude meter of the dual-axis device, and then the longitude and latitude, and the azimuth angle (relative to the north angle), of the drone can be analyzed. In this paper, the drone longitude and latitude coordinates [20,21] can be obtained by using the target coordinate conversion equation. A schematic diagram of the longitude and latitude coordinate algorithm of the target drone is shown in Figure 7. This algorithm is applicable to the distance calculation between any two points on the spherical surface, where O is the center point of the sphere, and A and B are any two points on the sphere. Point A represents the longitude and latitude coordinates \((W_{A},J_{A})\) obtained by the GPS in the dual-axis tracing platform, and point B represents the unknown longitude and latitude coordinates \((W_{B},J_{B})\) of the drone traced by the dual-axis tracing platform. The longitude and latitude coordinates of point B can be obtained by the sphere longitude and latitude coordinate conversion [21].