Fig. 1. Boundary tracing schematic and chain code representation and coordinate diagram. (a) Schematic diagram of clockwise boundary tracing; (b) chain code representation and coordinate plot

Fig. 2. Light penetration images of the ice surface. (a) (b) Light spot interference and local magnification; (c) (d) line width variation and local magnification

Fig. 3. Laser and spot boundary diagrams. (a) (b) (c) Original laser and spot diagrams; (d) (e) (f) laser and spot contour diagrams

Fig. 4. Schematic diagram of the search path for boundary tracking

Fig. 5. Flowchart of preliminary extraction of center point

Fig. 6. Flowchart of laser stripe center extraction of sub-pixel center point

Fig. 7. Schematic diagram of bilinear interpolation

Fig. 8. Schematic diagram of accurate extraction of laser stripe center coordinates

Fig. 9. Center point and normal direction diagram

Fig. 10. Schematic diagram of visual measurement system

Fig. 11. Original images of the surface of the ice body with diffused light spot and the extraction effect of multiple algorithms. (a) Original images;(b) gray gravity algorithm; (c) Steger algorithm; (d) skeleton algorithm; (e) algorithm of reference [13]; (f) algorithm of reference [16]; (g) algorithm of reference [17]; (h) proposed algorithm

Fig. 12. Original images of laser stripes with curvature change, comparison of extraction effects of multiple algorithms, and local enlargement images. (a) Original images;(b) gray gravity algorithm; (c) Steger algorithm; (d) skeleton algorithm; (e) algorithm of reference [13]; (f) algorithm of reference [16]; (g) algorithm of reference [17]; (h) proposed algorithm

Fig. 13. Original images of laser stripes with varying widths, comparison of extraction effects of various algorithms, and local enlargement images. (a) Original images;(b) gray gravity algorithm; (c) Steger algorithm; (d) skeleton algorithm; (e) algorithm of reference [13]; (f) algorithm of reference [16]; (g) algorithm of reference [17]; (h) proposed algorithm

Fig. 14. Schematic of laser stripes extraction on different ice surfaces. (a) Complex stripes with varying stripe line widths; (b) rough surface of the ice; (c) stripe boundaries are not obvious; (d) stripe line width widening

Fig. 15. Simulated light bar images. (a) $y=\mathrm{80}$; (b) $y=\mathrm{100}$; (c) $y=\mathrm{130}$

Fig. 16. Multiple algorithms for extracting coordinate scatter plots

Fig. 17. Root mean square error of simulated light bar centers for multiple algorithms

Fig. 18. Frost ice sphere surface reconstruction effect. (a) Real image of frost ice; (b) 3D point cloud of frost ice surface

Table 1. Error analysis of laser-centered coordinates on the surface of the ice

Table 2. Running time of different algorithms