## 5 Experimental Verification
### Binocular Ranging Experiment
#### 5.3.2 Distance Measurement  
Table 3 shows the results of multiple sets of ranging experiments on charging ports using the SGBM algorithm under different light intensities (1 st to 6 th rows: 20-500 k; 7 th row: 100,000 lx). The first six groups of data in the table are the test results of the binocular camera under randomly changing light within a small interval, and the last group is the test data under overexposure. The first three columns of the test results are the world coordinates (unit: mm) of the charging port relative to the left camera, and the three values are X (the horizontal direction of the captured image), Y (the vertical direction of the captured image), and Z (the distance between the camera and the charging port, i.e., depth). The fourth column is the actual distance of Z axis (Z\({}_{\text{A}}\)) and the last two columns are the calculated overall distance (CD) and the actual overall distance (AD), respectively. It can be seen from the table that under the current camera calibration state and slowly changing light, when the actual Z distance is 200 mm (the distance is measured by the scale), the test distance RMS error between the calculated overall distance and the actual overall distance of the first six rows is about 1.51 mm (0.755%), which is acceptable in practical applications (<2% requested).  
It should be noted that the test error of the binocular camera is large under overexposure (the last set of data), which is also a disadvantage of binocular visual ranging. However, as the charging facilities are generally placed indoors (such as underground parking spaces) or are equipped with a rain cover or a roof, which is necessary for the automatic charging system of the research, the situation of overexposure can be excluded. Figure 9(a) is the visual ranging result and Figure 9(b) is the scale ranging image.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**X** & **Y** & **Z** & **Z\({}_{\text{A}}\)** & **CD** & **AD** \\ \hline \(-13.8329\) & \(4.0394\) & \(198.3303\) & \(200\) & \(198.8531\) & \(201\) \\ \(-10.3983\) & \(-32.383\) & \(199.3371\) & \(200\) & \(202.2179\) & \(201\) \\ \(-20.1614\) & \(14.990\) & \(198.530\) & \(200\) & \(200.1133\) & \(201\) \\ \(-13.5946\) & \(4.6332\) & \(200.5588\) & \(200\) & \(201.0724\) & \(201\) \\ \(-14.6609\) & \(12.3290\) & \(201.5883\) & \(200\) & \(202.4964\) & \(201\) \\ \(-19.4849\) & \(47.2711\) & \(200.7639\) & \(200\) & \(207.1722\) & \(205\) \\ \(-57.71264\) & \(70.5011\) & \(283.3291\) & \(200\) & \(297.6181\) & \(220\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Binocular camera range results (unit: mm) under (1 st,..., 6 th rows) random change in light in normal range and (7 th row) an overexposure condition.  
Figure 10: Comparison of two measurement results: (**a**) Identification and distance measurement of charging port; (**b**) scale measurement results.  
Tables 4 and 5 show the results of multiple sets of ranging experiments on charging ports when the Z axis is 250 mm and 300 mm, respectively (under different light intensities from 20 k to 500 lx). X\({}_{\text{A}}\), Y\({}_{\text{A}}\), and Z\({}_{\text{A}}\) represent the actual distances of corresponding axes in each test. \(\mid\)e \(\mid\)1% means the error between the measured value and actual value of axis I (I = X, Y, Z) and \(\mid\)e \(\mid\)% is the error between the calculated overall distance (CD) and the actual overall distance (AD). Furthermore, the mean error of each axis is illustrated by \(\mid\)e \(\mid\)'1% (I = X, Y, Z) in the table below, from which it can be seen that although the errors in the X and Y axes are slightly bigger, the overall distance errors \(\mid\)e \(\mid\)' are 0.71% and 0.60% in Tables 4 and 5, respectively, which are still in the acceptable range.