# Research on Crack Width Measurement Based on Binocular Vision and Improved DeeplabV3+
## 4 Experiment and Analysis
### Crack Measurement Experiment  
In this section, the concrete crack width measurement method proposed in this paper is experimentally verified. The AYALEY adjustable baseline binocular camera is used in the experiment, and its maximum resolution is 1280 \(\times\) 960, as shown in Figure 13. Before measurement, the camera calibration toolbox in MATLAB is used to calculate the internal and external parameters of the camera. The experiment chooses to measure the crack of concrete pavement, and Figure 14 shows the four positions selected for the measurement. The central axis of the camera was made perpendicular to the concrete pavement for shooting, and the crack width was obtained by segmentation, edge extraction, and skeleton extraction of the four crack images respectively, as shown in Figure 15. The fourth column is the edge and skeleton extraction effect in the first red box, which shows that the crack edge extracted by the proposed algorithm is more accurate. Figure 14: The measured selected position (1, 2, 3, and 4) represent the locations of four crack measurements). Figure 13: Experimental equipment. To verify the accuracy of the proposed crack width measurement method, the measurement comparison experiment is carried out, as shown in Table 2. Methods 1, 2, and 3 represent the original DeeplabV3+ algorithm combined with the semi-global matching method, the original DeeplabV3+ algorithm combined with the proposed spatial coordinate acquisition method, and the improved DeeplabV3+ method combined with the proposed spatial coordinate acquisition method, respectively. HICHANCE-CK101 crack width measuring instrument (Measurement accuracy: 0.01 mm) was used to calculate the true value of the crack width by the average of three measurements. It can be seen from the measurement results in Table 2 that the absolute value of the error measured by method 1 to method 3 in this paper is gradually reduced, which verifies the effectiveness of the improved DeeplabV3+ algorithm and the space coordinate conversion algorithm proposed in this paper. Both of them can reduce the measurement error of the crack width, and the error rate of method 3 is less than 4% and the error value is less than 0.2 mm. To further prove the characteristics of easy deployment and \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**ID**} & \multirow{2}{*}{\begin{tabular}{c} **True** \\ **Value/mm** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Results of** \\ **Method** \\ **1/mm** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Error** \\ **Value/mm** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Rate of** \\ **Error/\%** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Results of** \\ **Method** \\ **2/mm** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Error** \\ **Value/mm** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Rate of** \\ **Error/\%** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Results of** \\ **Method** \\ **3/mm** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Error** \\ **Value/mm** \\ \end{tabular} } \\ \hline
1 & 5.412 & 6.025 & +0.613 & 11.33 & 5.876 & +0.464 & 8.57 & 5.586 & +0.174 & 3.22 \\
2 & 4.210 & 4.412 & +0.202 & 4.80 & 4.366 & +0.156 & 3.71 & 4.085 & \(-0.125\) & 2.97 \\
3 & 3.567 & 3.775 & +0.208 & 5.83 & 3.238 & \(-0.329\) & 9.22 & 3.696 & +0.129 & 3.62 \\
4 & 6.189 & 5.023 & \(-1.166\) & 18.84 & 5.848 & \(-0.341\) & 5.51 & 6.321 & +0.132 & 2.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Crack width measurement error. Figure 15: Concrete crack edge segmentation measurement example. stable measurement of this method, by fine-tuning the distance, the optical axis of the camera is adjusted to 90, 70, 50, 30, and 10 degrees from the concrete plane respectively.