## 4 Experimental Results and Analysis
### Testing and Evaluation  
To test the performance of the method, a standard sphere with a diameter of 50.80(+1.50/\(-\)1.00) mm, a flat board with flatness of 15 \(\upmu\)m, and a standard cylinder with a diameter of 68.00 mm were measured by the structured light system. The testing steps of the method are shown in Figure 13. First, the stripe pattern was projected on the subject and photographed, and then the 3D information of the subject was calculated. The structured light stripe cross-section was input into the model trained above to determine whether the stripe was defective or not. Then, the 3D point cloud corresponding to the stripe region with defects was removed. Finally, the measurement errors with and without processing were calculated and compared. The principle of the method proposed in this paper is to evaluate the stripe quality according to the grayscale distribution of the structured light stripe cross-section. The grayscale distributions in the dataset include the ones of stripes on many different typical materials and shapes of objects in actual measurement processes. In order to test the generalization performance, this paper tested objects such as a steel ball and a flat board which are not included in the training dataset. The measurement results of the spherical surface are shown in Figure 14. Figure 14a shows the modulated pattern on a standard ball. Figure 14b shows the 3D point cloud of the ball, and Figure 14c,d shows the concentration areas of large errors in the data. The ball in Figure 14b is obtained by fitting the measurement data to a sphere. Although the intensity of Figure 14c is high, the skewness coefficient of the stripe is high because of specular reflection. In Figure 14d, the noise is largely due to the low intensity of the stripe. The measurement error of the ball is defined as the difference of the fitted radius and the  
Figure 12: Loss Curve. Figure 13: Validation Process Flow Chart. distance between the measurement 3D point and the fitted center of the ball, which can be defined as:  
\[\text{Error}=|\,\text{d}-\text{d}^{\prime}\,| \tag{2}\]  
where d is the actual distance from the sphere to the center of the sphere; d' is the distance of each point of the 3D point cloud from the center of the fitted sphere. Since the gray distribution of the structured light stripes cross-section corresponding to points with large measurement errors in the point cloud tends to be degraded, the points with large measurement errors are considered defective. The stripe cross-sections are intercepted in Figure 14a and input into the prediction algorithm. The algorithm uses the model trained in Section 4.2 as the prediction model to transform the cross-sectional images into grayscale curves and perform prediction, and the results are shown in Figure 15. The grayscale distribution of the defective stripes in Figure 15a-d comes from the irregular regions in Figure 14c,d, and the grayscale distribution of the defect-free stripes in Figure 15e-h comes from the region with better stripe quality in Figure 14a. According to the prediction results, the stripe cross-sections at the locations corresponding to the irregular regions in Figure 14c,d both have serious defects and are evaluated as \"bad\" by the prediction algorithm. In addition, the stripe cross-sections intercepted in regions with a good-quality of stripe are all evaluated as defect-free by the prediction algorithm. This is consistent with the conclusions obtained through the criteria for judging the quality of stripe cross-sections in Section 3.2, as expected. The measurement errors of the points corresponding to each stripe cross-section in Figure 15 in the 3D point cloud are shown in Table 6. It can be seen that during the evaluation of stripe quality, stripe cross-sections evaluated as defective have large measurement errors in their corresponding area. On the contrary, the points corresponding to the defect-free stripe sections tend to have smaller measurement errors. The results verified the prediction results.