## 2 System Architecture
### Drone Visual Image Tracing Method
When the target drone's image enters the edge of the rectangular frame of the tracing device, it is acquired by the visual identification of the system. The tracing system instantly estimates the pixel difference \((p,q)\) between the \(x\)-axis and the \(y\)-axis of the center position \((x_{2},y_{2})\) and the concentric point \((x_{1},y_{1})\) of the drone: \((x_{2}-x_{1},y_{2}-y_{1})\). When the p value is positive, it reveals that the center point of the target drone is on the right side of the center point of the screen image, and vice versa for the left side. Furthermore, when the q value is positive, it reveals that the center point of the target drone is on the lower side of the center point of the screen image, and vice versa. Figure 3: Drone image acquisition procedures. In order to trace the invading drones dynamic position at any time, three-dimensional coordinate parameters such as the flight altitude of the drone and its longitude and latitude are calculated, and these parameters are immediately transmitted to the ground monitoring center for direct attack or indirect hunt for the drone. The control requirements for a two-axis step motor in the dual-axis tracing device are as follows:  
Suppose the position of the concentric point of the screen image is \((x_{1},y_{1})\) and the position of the drone is \((x_{2},y_{2})\), which are shown in Figure 4. The system traces the drone in real time, and the requirement of motor control speed of the dual-axis device is:  
\[V_{yun-rotation}=\frac{p}{\Delta t}\textit{ and }V_{pitch-rotation}=\frac{q}{ \Delta t} \tag{4}\]  
where \(\Delta t\) is the time for the duration of the image capture card to acquire images, which is normally 30 frames per second; that is, \(\Delta t\) = 1/30 s. The smaller the value of \(\Delta t\), the more accurately the tracing system can grasp the drone movement trajectory, so that the alignment screen's concentric point of the tracing device can lock the drone as soon as possible, but relatively requires a faster software computing requirement. The system has to convert the pixel difference (\(p\), \(q\)) of the image into the tracing step angle of the two-axis step motor of the tracing device; that is, the image coordinates are converted from pixel values (\(p\), \(q\)) to the number of steps (\(S_{p}\), \(S_{q}\)) to drive the two-axis step motor, where \(Sp\) and \(Sq\) represent the step numbers of the step motor for the yaw rotation and pitch rotation, respectively. Since the step motor rotates 360\({}^{\circ}\) in one turn, assuming that \(\mathrm{S_{R}}\) is the total number of steps in one circle of the step motor, the step angle \(\theta_{m}\) of each step motor is:  
Figure 1:0  
Due to the fact that the necessary \(\theta_{m}\) value of the step motor in the tracing device is related to the pixel value acquired by the image capture card, it is important to find the correlation between these two matters. First, suppose the full-color (or thermal imaging) camera acquires the picture in a certain direction as shown in Figure 5a. Then, suppose the driver of the step motor in the tracing device send the square wave signal with the number of \(S_{P}\) to the step motor of the \(x\)-axis, which drives the step motor of the \(x\)-axis to carry out the rotation of \(\mathrm{S_{P}}\) steps. These make the dual-axis device carry out a horizontal right movement, and then acquires the immediate picture, as shown in Figure 5b. Finally, by comparing the images of Figure 5a,b with the superimposed image and calculating the  
Figure 1:1 Diagram of the target drone displacement vector. increment of the p-value of these two images of the \(x\)-axis after the step motor of the \(x\)-axis rotates steps of \(S_{p}\), as shown in Figure 5c, the tracing system can receive the number of steps \(p_{S}\) of the step motor necessary for each pixel in the yaw rotation direction:  
Figure 1:2  
Furthermore, the number of steps of the step motor necessary for each pixel in the pitch rotation direction is \(q_{S}\). Figure 1:3