## 3 Experimental Result

Table 2: Comparison of the registration results between the proposed algorithm and the other algorithms. Part of the CAD bullet point cloud obtained from the above five different angles was used for the registration experiments, and the proposed algorithm was compared with the ICP, TRICP, and GOICP algorithms. The ICP algorithm is a classical registration algorithm that is easy to implement and has a high efficiency, but is easily affected by the initial position. The TRICP algorithm provides a more robust registration method by improving the ability to deal with outliers and partial overlaps through a pruning mechanism; the GOICP algorithm is committed to solving the local optimal problem of the ICP algorithm and providing the global optimal solution, but the calculation cost is high. The experimental results are shown in Table 2. It can be seen that the proposed algorithm \begin{table}
\begin{tabular}{c c}  & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 6: The three-dimensional topography of the warhead collected from five different angles. has a good registration effect when the overlap rate is greater than 20%, while the ICP algorithm fails when the overlap rate is lower than 40%. At the same time, we use the mean distance error, nearest neighbor distance error, Hausdorff distance, and root error for the overlapping regions of the mean square as the registration error, where the smaller the registration error, the better the registration effect. It can be seen from Tables 3-6 that the registration algorithm proposed in this paper has a high speed and high registration accuracy. When the overlap rate is large, the registration accuracy of these registration algorithms is similar. With the decrease in the overlap rate when the overlap rate is not less than 20%, the registration algorithm proposed in this paper has a higher registration accuracy than the ICP, TRICP, and GOICP algorithms. a stable error value close to zero when the overlap rate is not less than 20%, which indicates that the alignment algorithm in this paper is very effective in dealing with the current point cloud data, and can accurately find the best alignment transform. According to the actual project requirements, an automatic zoom microscope was used in this paper to collect bullet data, as shown in Figure 8. The autozoom microscope combines the function of a surface roughness measuring instrument with that of a topography measuring instrument based on the focus change technology. The focus change technique combines the small-range depth focus of an optical system with vertical scan detection to provide morphology and color information from the focus change. The main part of the system consists of a precision optical device containing a variety of lens systems that can be equipped with different objectives, thus achieving measurements of different resolutions. Precision optics move vertically along the optical axis while continuously capturing data from the surface. This means that each area of the object can be clearly focused for imaging and subsequently convert the acquired sensor data into 3D point cloud data. The test object of this experiment is a bullet, and two point clouds of the tested object under different viewing angles are obtained. The overlapping part of the point cloud from the two viewing angles can be extracted in pairs through the point cloud overlapping part extraction algorithm. The details are shown in Figures 9 and 10. Figure 7: Error comparison graph between the proposed algorithm and the ICP and its variants: (**a**) RMS error curve comparison graph; (**b**) NNED error curve comparison chart; (**c**) HD error curve comparison diagram; (**d**) MED error curve comparison chart. An automatic zoom microscope was used to carry out the morphological measurements of the bullet marks of 9 mm pistol bullets. In this paper, the key parts of the bullet marks were selected for acquisition with higher precision and were more conducive to achieving high-precision registration.