Fig. 1. Calculation of normal vector by PCA

Fig. 2. Point projection

Fig. 3. Hausdorff distance

Fig. 4. Indian Tunnel point cloud data

Fig. 5. Feature area point cloud

Fig. 6. Lava tube morphology analysis

Fig. 7. Height， width and aspect ratio of lava tube cross-section

Fig. 8. Error of resampled point cloud

Fig. 9. Error of reconstructed surface

Fig. 10. Comparison of different resampling algorithm

Fig. 11. Comparison of reconstructed surfaces by ball-pivoting and OSR