Automatic extraction of blocks from 3D point clouds of fractured rock

• Published in: Computers & geosciences Vol. 109; pp. 149 - 161
• Main Authors: Chen, Na, Kemeny, John, Jiang, Qinghui, Pan, Zhiwen
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-12-2017
• Subjects: 3D point clouds; Automatic extraction; Block size; Discontinuity orientation; Rock mass; 3D point clouds; Automatic extraction; Rock mass; Block size; Discontinuity orientation
• ISSN: 0098-3004; 1873-7803
• DOI: 10.1016/j.cageo.2017.08.013

This paper presents a new method for extracting blocks and calculating block size automatically from rock surface 3D point clouds. Block size is an important rock mass characteristic and forms the basis for several rock mass classification schemes. The proposed method consists of four steps: 1) the automatic extraction of discontinuities using an improved Ransac Shape Detection method, 2) the calculation of discontinuity intersections based on plane geometry, 3) the extraction of block candidates based on three discontinuities intersecting one another to form corners, and 4) the identification of “true” blocks using an improved Floodfill algorithm. The calculated block sizes were compared with manual measurements in two case studies, one with fabricated cardboard blocks and the other from an actual rock mass outcrop. The results demonstrate that the proposed method is accurate and overcomes the inaccuracies, safety hazards, and biases of traditional techniques.
•A new method is developed to automatically extract blocks from rock outcrops.•The extraction of block information is based on raw point clouds.•An improved Ransac algorithm was used to extract the discontinuity information.•A “Plane number algorithm” was developed to identify block candidates.•The “Floodfill algorithm” was used to distinguish true from “molds” of blocks.