Automatic identification of discontinuities and refined modeling of rock blocks from 3D point cloud data of rock surfaces

The spatial distribution of discontinuities and the size of rock blocks are the key indicators for rock mass quality evaluation and rockfall risk assessment. Traditional manual measurement is often dangerous or unreachable at some high-steep rock slopes. In contrast, unmanned aerial vehicle (UAV) photogrammetry is not limited by terrain conditions, and can efficiently collect high-precision three-dimensional (3D) point clouds of rock masses through all-round and multiangle photography for rock mass characterization. In this paper, a new method based on a 3D point cloud is proposed for discontinuity identification and refined rock block modeling. The method is based on four steps: (1) Establish a point cloud spatial topology, and calculate the point cloud normal vector and average point spacing based on several machine learning algorithms; (2) Extract discontinuities using the density-based spatial clustering of applications with noise (DBSCAN) algorithm and fit the discontinuity plane by combining principal component analysis (PCA) with the natural breaks (NB) method; (3) Propose a method of inserting points in the line segment to generate an embedded discontinuity point cloud; and (4) Adopt a Poisson reconstruction method for refined rock block modeling. The proposed method was applied to an outcrop of an ultrahigh steep rock slope and compared with the results of previous studies and manual surveys. The results show that the method can eliminate the influence of discontinuity undulations on the orientation measurement and describe the local concave-convex characteristics on the modeling of rock blocks. The calculation results are accurate and reliable, which can meet the practical requirements of engineering.