## 4 Experimental Results and Discussion
### Performance Analysis on Satellite Image Pair
In order to be consistent with the ground truth in Figure 4, we still represent the generated DSMs as RGB images in Figure 6, and the altitude range is still 18-35 m. It can be seen from the first column of Figure 6 that there are many holes in the most DSMs generated by the S2P method, and their visual quality is poor. As for image pairs 4, 8, and 10, although the S2P method generates fewer holes in the DSM, it can be seen that the altitude error of the DSM is large according to the image color. It can be seen that the color of DSM generated by image pair 10 is closer to the ground truth than image pair 4 and image pair 8. The altitude errors of the DSMs corresponding to image pairs 4, 8, and 10 are about 3 m, 2 m, and 1 m, respectively, which also proves the previous inference. However, the DSM generated from image pair 5 is better because the S2P method relies heavily on the results of geometric stereo rectification. When the stereo rectification result is poor, it will lead to more mismatches in the subsequent stereo matching process, resulting in poor accuracy of the generated DSMs. As shown in the second and third columns of Figure 6, the altitude information of the DSMs generated by the traditional BA method is similar to that of the proposed method. The generated DSMs of the proposed method and the traditional BA method are closer to the ground truth DSM. As can be seen from the ten sets of DSMs, the DSM generated by  
Figure 5: The DSM generated from: (**a**) the satellite image pair with more than 30\({}^{\circ}\) sun angle difference; (**b**) the satellite image pair with more than 20\({}^{\circ}\) intersection angle. image pair 4 appears green at some roads on the image, which is different from the blue color of the ground truth DSM, so the altitude error here is large. This may be due to the large intersection angle of image pair 4. In addition, the DSMs generated by image pair 6 and image pair 7 have more holes, which is due to the fact that there are fewer matching points, and the deeper reason is that the sun angle differences of these two image pairs are too large (more than \(20^{\circ}\)). It can be seen that the visual quality of the DSMs generated by image pairs 8, 9, and 10 is better than that generated by image pairs 6 and 7, which indicates that even if the acquisition interval is large, as long as the sun angle difference and the intersection angle of the image pair are appropriate, the DSMs with better visual quality can be generated. In general, the DSMs generated by the proposed method appear to be very similar to the traditional BA method in Figure 6. However, in fact they are slightly different, and it is more obvious at the intersection in the upper right corner of image pair 9, where the 3D points generated by the proposed method are denser. The details of image pair 9 are shown in Figure 7. As for the comparison between the proposed method and the traditional BA method, it is necessary to further calculate the quality evaluation of the generated DSMs. The results of the quality evaluation experiments are listed in Table 3. The metrics in bold are the best of the three methods. According to the metrics in Section 4.1, we hope that the CP of the generation result is as high as possible, and a higher CP means more good points (points with an altitude accuracy better than 1 m) in the generated DSM. At the same time, we also hope that the ME is as low as possible, and lower ME means higher accuracy of the generated DSM. Figure 6: The generated DSMs of the S2P method [7], the traditional BA method [32], and the proposed method. acquisition interval of the image pair. However, the CP of the DSM generated by image pair 9 and image pair 10 is better than that of image pair 8. Because the acquisition interval of image pair 8 is 152 days, and the two satellite images of image pair 8 are acquired in autumn and spring, respectively, which will cause large differences in surface vegetation, thus affecting the stereo matching step.