## 4 Results and Discussion
### Experiment of 2D-3D Registration
#### 4.1.4 MP-IDSSC Experiment
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Trials** & **Image** & **NCM** & **RMSE** & **CP** & **CP(m)** & **CO** & **CO (_urrad_)** \\ \hline \multirow{6}{*}{Trial 1} & \multirow{6}{*}{P1} & \multirow{6}{*}{332} & \multirow{6}{*}{0.60} & \(-2093392.02\) & 2.15 & 270.81 & 19.89 \\ \cline{3-8}  & & & & 4806196.97 & 2.83 & \(-7.39\) & 28.18 \\ \cline{3-8}  & & & & 3621103.69 & 3.77 & 354.87 & 20.76 \\ \cline{3-8}  & & & & \(-2093851.7\) & 0.44 & 221.33 & 19.63 \\ \cline{3-8}  & & & & 4806372.58 & 0.89 & 9.48 & 20.07 \\ \cline{3-8}  & & & & 3620501.74 & 1.18 & 0.70 & 12.13 \\ \hline \multirow{6}{*}{Trial 2} & \multirow{6}{*}{P1} & \multirow{6}{*}{223} & \multirow{6}{*}{1.83} & \(-2093390.58\) & 3.59 & 271.37 & 29.67 \\ \cline{3-8}  & & & & 4806196.99 & 2.85 & \(-7.78\) & 34.99 \\ \cline{3-8}  & & & & 3621102.49 & 4.97 & 355.83 & 37.61 \\ \cline{3-8}  & & & & \(-2093851.79\) & 0.56 & 221.29 & 20.42 \\ \cline{3-8}  & & & & 4806372.7 & 1.01 & 9.16 & 25.56 \\ \cline{3-8}  & & & & 3620501.78 & 1.60 & 0.73 & 11.51 \\ \hline \multirow{6}{*}{Trial 3} & \multirow{6}{*}{P1} & \multirow{6}{*}{173} & \multirow{6}{*}{0.86} & \(-2093392.05\) & 2.18 & 271.31 & 28.53 \\ \cline{3-8}  & & & & 4806197.18 & 3.05 & \(-10.02\) & 74.00 \\ \cline{3-8}  & & & & 3621100.77 & 6.69 & 356.40 & 47.56 \\ \cline{3-8}  & & & & \(-2093851.84\) & 0.61 & 221.28 & 20.68 \\ \cline{3-8}  & & & & 4806372.32 & 0.63 & 8.60 & 35.34 \\ \cline{3-8}  & & & & 3620501.88 & 2.23 & 0.81 & 10.03 \\ \hline \multirow{6}{*}{Trial 4} & \multirow{6}{*}{P1} & \multirow{6}{*}{182} & \multirow{6}{*}{0.82} & \(-2093392.95\) & 1.22 & 271.33 & 28.97 \\ \cline{3-8}  & & & & 4806197.72 & 3.58 & \(-10.03\) & 74.17 \\ \cline{3-8}  & & & & 3621100.53 & 6.93 & 356.38 & 47.21 \\ \cline{3-8}  & & & & \(-2093851.6\) & 0.40 & 221.33 & 19.72 \\ \cline{3-8}  & & & & 4806372.82 & 1.13 & 8.455 & 37.96 \\ \cline{3-8}  & & & & 3620500.33 & 1.79 & 0.685 & 12.30 \\ \hline \multirow{6}{*}{Trial 5} & \multirow{6}{*}{P1} & \multirow{6}{*}{30} & \multirow{6}{*}{1.89} & \(-2093391.17\) & 3.00 & 271.55 & 32.81 \\ \cline{3-8}  & & & & 4806196.71 & 2.57 & \(-9.75\) & 69.37 \\ \cline{3-8}  & & & & 3621098.40 & 9.06 & 356.13 & 42.84 \\ \cline{3-8}  & & & & \(-2093851.7\) & 0.43 & 221.25 & 21.11 \\ \cline{3-8}  & & & & 4806373.89 & 2.20 & 8.34 & 39.88 \\ \cline{3-8}  & & & & 3620498.87 & 3.24 & 0.7 & 12.04 \\ \hline \multirow{6}{*}{Trial 6} & \multirow{6}{*}{P1} & \multirow{6}{*}{13} & \multirow{6}{*}{1.05} & \(-2093246.81\) & 147.36 & 183.38 & 1506.04 \\ \cline{3-8}  & & & & 4806182.10 & 12.03 & \(-34.71\) & 504.92 \\ \cline{3-8}  & & & & 3621131.57 & 24.11 & 76.59 & 1447.05 \\ \cline{1-1} \cline{3-8}  & & & & \(-2093842.5\) & 8.77 & 218.86 & 23.38 \\ \cline{1-1} \cline{3-8}  & & & & 4806368.51 & 3.17 & 17.66 & 162.83 \\ \cline{1-1} \cline{3-8}  & & & & 3620501.05 & 1.07 & 7.16 & 124.96 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experimental Results of MP-IDSSC. and rolling angle error. This is because real images contain sky, trees, and barren ground, resulting in an uneven vertical distribution of feature points in the image. It can also be seen in Figures 7 and 8 that in the image matching results, there are more feature points in the middle of the image, while there are fewer feature points in the upper and lower parts. This leads to insufficient constraints in the vertical direction, resulting in a large vertical error. In Trials 1-2, because this method uses the structural semantic information in the image and the direction of the plumb line to constrain, the error in the vertical direction is significantly reduced. Comparing Trials 4-5, our IDSSC-MP method obtains better results when the same feature point extraction algorithm is used. In Trials 4-5, the average error of the Z-coordinate is 5.26 m, but 2.88 m in Trials 1-2, which is 45% less than that in Trials 4-5. In Trials 1-2, the accuracy of the NCM and RMS is also higher, and the calculated camera position and attitude errors are smaller, which shows the effectiveness of the MP-IDSSC method.