Fig. 1. Neighborhood distribution corresponding to different eigenvalues when λ₃≈0. (a) λ₁≈λ₂≠0; (b) λ₁>λ₂≠0; (c) λ₁>λ₂≈0

Fig. 2. Hole feature line connection with reference to distance only. (a) Hole polygon; (b) sawtooth; (c) reentry

Fig. 3. Sorting of hole boundary points in minimum spanning tree. (a) Minimum generated graph of boundary; (b) state of each point after four iterations, the arrow points to the parent node; (c) gray points appear in the adjacent points, which means that a hole outline is found; (d) final extracted hole polygon

Fig. 4. Extraction effect of hole boundary in the car rocker point cloud model. (a) Point cloud near the hole; (b) minimum generated map; (c) extracted hole polygon

Fig. 5. Comparison of boundary detection effects of bucket teeth model. (a) Hole extracted by the algorithm in Ref. [15] and its enlargement; (b)(d) hole extracted by the algorithm in this paper and its enlargement

Fig. 6. Comparison of boundary detection effect of chain link model. (a)(c)Hole extracted by the algorithm in Ref. [15] and its enlargement; (b)(d) hole extracted by the algorithm in this paper and its enlargement

Fig. 7. Comparison of boundary detection effect of knuckle model. (a) Boundary detection result containing more misjudgment points; (b) the algorithm in Ref. [15] fails to extract hole polygon;(c) hole polygon extracted by the algorithm in this paper