## 5 Experimental Validation
To ensure that both the anchoring hole and the laser spot on the coal wall were simultaneously visible on the camera's imaging plane, the proposed method was used to measure the spatial pose of the anchoring hole. To validate the effectiveness and accuracy of the proposed method, experiments were conducted at six different positions by adjusting the bracket. An inclination sensor and a total station were used to measure the spatial pose of the anchoring hole, with their measurements serving as the ground truth. The results obtained using the proposed method were compared with the ground truth values. The experimental feature extraction results are shown in Figure 9.  
As shown in Figure 9, the images captured by the monocular camera at six different positions include the laser spots from the three laser pointers on the coal wall as well as the anchoring hole images on the steel strip. It can be observed that the proposed method successfully extracts both the anchoring holes and the laser spots. The anchoring-hole pose measurement results at six different positions are shown in Table 3. The calculated values correspond to the results obtained using the proposed method, while the true values correspond to the anchoring-hole pose measurements obtained using the inclination sensor and total station. To visually demonstrate the effectiveness and accuracy of the proposed method for anchoring-hole pose detection, the errors between the calculated values and the true values were computed. These errors are presented as the measurement errors of the proposed method for anchoring-hole pose detection, as shown in Table 4.  
As can be seen from Table 4, the average errors in the spatial positions of the anchoring holes along the XYZ axes were 3.36 mm, 3.30 mm, and 5.75 mm, respectively, with maximum errors of 4.23 mm, 4.39 mm, and 6.63 mm. The corresponding pitch, yaw, and roll angle errors had average values of 0.16\({}^{\circ}\), 0.16\({}^{\circ}\), and 0.08\({}^{\circ}\), with maximum errors of 0.21\({}^{\circ}\), 0.27\({}^{\circ}\), and 0.13\({}^{\circ}\). The experimental results verified the effectiveness and accuracy of the proposed visual positioning method for anchoring holes, which is crucial for improving the efficiency of coal mine roof support. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Coordinates**} & \multicolumn{3}{c}{**Calibration Results/mm**} \\ \cline{2-4}  & \(\boldsymbol{i=1}\) & \(\boldsymbol{i=2}\) & \(\boldsymbol{i=3}\) \\ \hline \(O_{c}\) & & (0.00, 1432.00, 272.60) & \\ \(P_{i}\) & (182.60, 1310.70, 431.50) & (\(-\)173.10, 1312.10, 452.00) & (180.90, 1310.40, 51.10) \\ \(Q_{i}\) & (197.10, 875.40, 502.00) & (\(-\)201.00, 882.30, 537.20) & (210.80, 874.90, 74.30) \\ \(s_{L_{i}}\) & (\(-\)70.50, \(-\)14.50, 435.30) & (\(-\)85.20, 27.90, 429.80) & (\(-\)23.20, \(-\)29.90, 435.50) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameter calibration results of the steel belt–anchor hole pose visual measurement unit. It can be seen that the measurement error of the system is smaller when the angle between the camera's imaging plane and the coal wall plane is smaller, and vice versa, the measurement error is larger. In addition, since the method presented in this paper is based on the triangulation principle, the measurement error increases when the measurement distance increases. However, according to the maximum positioning error allowed in the construction of a steel belt support in an underground coal mine tunnel, within a  
Figure 9: Experimental feature extraction results: (**a**) Position 1; (**b**) Position 4; (**c**) Position 2; (**d**) Position 5; (**e**) Position 3; (**f**) Position 6.  
certain measurement range, the steel belt-anchor hole positioning method based on monocular vision and its feature extraction method proposed in this paper meet the relevant requirements.