Fig. 1. Target layout

Fig. 2. Algorithm flow chart

Fig. 3. Sorting of feature points

Fig. 4. Schematic diagram of the Epnp algorithm

Fig. 5. Relationship between camera coordinate system and world coordinate system

Fig. 6. Optimize flow chart

Fig. 7. Graph with outliers

Fig. 8. Graph without outliers

Fig. 9. Schematic diagram of the ICP algorithm

Fig. 10. Diagram of test equipment

Fig. 11. Experimental results of X-axis unidirectional movement. (a) Three-axis displacement change value; (b) three-axis error value

Fig. 12. Experimental results of Y-axis unidirectional movement. (a) Three-axis displacement change value; (b) three-axis error value

Fig. 13. Experimental results of Z-axis unidirectional movement. (a) Three-axis displacement change value ; (b) three-axis error value

Fig. 14. Stability error analysis of each axis. (a) Stability error value of X-axis unidirectional displacement; (b) stability error value of Y-axis unidirectional displacement; (c) stability error value of Z-axis unidirectional displacement

Fig. 15. Experimental results of three-axis movement displacement. (a) Three-axis displacement change value; (b) three-axis error value

Fig. 16. Outdoor experimental analysis diagram. (a) Crack diagram of outdoor experimental dam; (b) comparison of detection error