## 2 System Architecture and Hardware Layout  
### Selection and Layout of Consumer Cameras  
Explosives transport vehicles belong to a type of dangerous goods transport vehicles. According to _Road Transport Safety Management Measures for Dangerous Goods_ of China, the speed regulations for dangerous goods transport vehicles are as follows: dangerous goods transport vehicles cannot exceed 80 km per hour on highways and cannot exceed 60 km per hour on other roads. If the speed indicated on road speed limit signs or markings is lower than the prescribed speed, the vehicle shall not exceed the indicated speed limit. Additionally, Article 80 of the _Implementation Regulations of the Road Traffic Safety Law of the People's Republic of China_ stipulates that when a motor vehicle is driving on a highway and its speed exceeds 100 km per hour, vehicles must maintain a distance of more than 100 m from the vehicle in front of the same lane. When the speed is less than 100 km per hour, and the distance from the vehicle in front of the same lane can be appropriately shortened, the minimum distance should not be less than 50 m. Therefore, while meeting the driving standards of explosives transport vehicles, taking into account the safety requirements of explosives transport vehicles in actual explosives transport and the error of consumer-grade camera ranging, the monitoring standards are set at a speed of 60 km per hour, a safe following distance of 50 m for front and rear vehicles, and a 2 m distance from surrounding vehicles. Focal length is the distance from the optical center of the lens to the imaging plane. The smaller the focal length of the camera, the stronger its ability to concentrate light, the wider the viewing range, and the closer the viewing distance. Conversely, the larger the focal length of the camera, the weaker its ability to concentrate light, the narrower the viewing range, and the farther the viewing distance. The system monitors two types of distances: the distance between the front and rear vehicles during transportation and the surrounding vehicles. Therefore, based on the optical characteristics of the camera and the functional requirements of the system, the appropriate camera (Tianjin, China) and its parameters are selected, as shown in Table 2.  
The schematic diagram of the monitoring range of the binocular camera is shown in Figure 2, where the sector depicts the field of view of a single camera, and the gray part represents the overlap of the two sectors (i.e., the monitoring range of the binocular camera). \(\theta\) is the horizontal field of view angle of the camera, \(d\) is the baseline distance between two cameras, and \(x\) is the length of the monitoring blind zone. The length of the monitoring blind zone \(x\) is proportional to the baseline distance \(d\), and \(d\) can be determined as Equation (1). \[d=2x\sqrt{\frac{1-cos\theta}{1+cos\theta}} \tag{1}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Function** & **Camera Model** & **Focal Length** &
\begin{tabular}{c} **Horizontal Field** \\ **of View Angle** \\ \end{tabular} & **Detection Distance** \\ \hline I & Monocular camera & & 12 mm & 27\({}^{\circ}\) & 80 m \\ \hline II & Binocular camera & & 4 mm & 70\({}^{\circ}\) & 50 m \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Camera model selection [24]. The blind zone distance \(x\) of binocular monitoring must be less than the safety threshold of the system. Based on Equation (1) and the monitoring standard of a 2 m surrounding safety distance, the maximum baseline distance \(d_{max}\) of binocular cameras II listed in Table 1 is calculated using Equation (2):  
\[\theta=70^{\circ},\,x=2\,\,\text{m},\,d_{max}=2\chi\sqrt{\frac{1-cos\theta}{1+ cos\theta}}=2\times 2\times\sqrt{\frac{1-0.34}{1+0.34}}\approx 2.81\,\,\text{m} \tag{2}\]  
A box truck (6 m long, 2.2 m wide, and 2.3 m high) was selected to evaluate the camera layout.