# Vehicle Distance Measurement Method of Two-Way Two-Lane Roads Based on Monocular Vision
## 3 Experiments and Discussions
### Distance Measurement Experiment and Analysis of Results  
In order to verify the feasibility and effectiveness of the vehicle distance measurement method of two-way two-lane roads and the improved geometric ranging method, a distance measurement experiment with actual vehicles was carried out on actual two-way two-lane roads. To avoid the interference of too many vehicles coming and going, the experiment was carried out on a 200-meter-long, horizontal, and straight two-way two-lane road on campus. Figure 8 shows one of the experimental scenes. As shown in Figure 8, three cars named A, B, and C, respectively, were prepared to restore the actual vehicle position on the two-way two-lane roads. As the main test vehicle with an on-board camera, car A collected the video of the road ahead from the first perspective and was placed on one lane of the two-way two-lane road; car B was the forward vehicle on the same lane in front of car A, and back-facing car A; car C was the opposite car on the opposite lane in front of car A, and facing car A. The TC411 HD camera was used as the video capture device, and the long ruler was used as the distance measurement tool. Before the experiment, in order to capture the car on the opposite lane more clearly, the camera was installed near the A pillar of car A, and the angle of the camera was adjusted to make car B and car C appear completely on the video screen. Zhang Zhengyou calibration method [31] was used to calibrate the focal length \(f\) of the camera, the coordinates (\(u_{0}\), \(v_{0}\)) of the center point of the image plane, and other parameters. Then, the height \(h\) of the camera's optical center from the ground, the pitch angle \(\alpha\), and the roll angle \(\theta\) of the camera were measured. The longitudinal distance from the camera to the head of car A was 1.9 m. The camera parameters are listed in Table 3.  
In order to ensure the ranging accuracy, this paper adopted the way of static distance measurement; that is, the three cars remained stationary while the distance was being measured. Based on the relationship between vehicles before overtaking on two-way two-lane roads, the ranging range of car B was set to be 0-60 m in front of car A, while that of car C was 60-120 m in front of car A. During the experiment, car A remained stationary; car  
Figure 8: One of the experimental scenes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{4}{c}{**Internal Parameters**} & \multicolumn{4}{c}{**External Parameters**} \\ \cline{2-7}  & \(f\) **(Pixel)** & \(u_{0}\) **(Pixel)** & \(v_{0}\) **(Pixel)** &
\begin{tabular}{c} **Image Size** \\ **(Pixel)** \\ \end{tabular} & \(h\) **(m)** & \(\theta\) (\({}^{\circ}\)) & \(\alpha\) (\({}^{\circ}\)) \\ \hline value & 1223.3 & 630.1 & 372.3 & 1280 \(\times\) 720 & 1.18 & \(-\)1.27 \({}^{\ast}\) & \(-\)1.03 \({}^{\ast}\) \\ \hline \hline \end{tabular}  
\({}^{\ast}\) The positive and negative signs indicate that the camera rotates counterclockwise and clockwise around the optical axis, respectively.  
\end{table} 
Table 3: Parameters of on-board camera. B and car C stopped after moving a certain distance within their respective ranging range, and video recorded the pictures containing car B and car C at this time. The long ruler was used to measure the longitudinal distance between the projection point of car A's head to the ground to the projection point of car B's head to the ground, and the longitudinal distance between the projection point of car A's head to the ground to the projection point of car C's head to the ground, and record them. The above operations were repeated, and a total of 13 groups of data were measured, ranging from 0 to 120 m.  
The trained vehicle detection model and ranging algorithm were connected in series. The collected experimental video data were used as the input of the whole model, and the output of the model was recorded.