Explainable artificial intelligence for rock discontinuity detection from point cloud with ensemble methods

This study presents a framework for the semi-automatic detection of rock discontinuities using a three-dimensional (3D) point cloud (PC). The process begins by selecting an appropriate neighborhood size, a critical step for feature extraction from the PC. The effects of different neighborhood sizes (k = 5, 10, 20, 50, and 100) have been evaluated to assess their impact on classification performance. After that, 17 geometric and spatial features were extracted from the PC. Next, ensemble methods, AdaBoost.M2, random forest, and decision tree, have been compared with Artificial Neural Networks to classify the main discontinuity sets. The McNemar test indicates that the classifiers are statistically significant. The random forest classifier consistently achieves the highest performance with an accuracy exceeding 95% when using a neighborhood size of k = 100, while recall, F-score, and Cohen's Kappa also demonstrate high success. SHapley Additive exPlanations (SHAP), an Explainable AI technique, has been used to evaluate feature importance and improve the explainability of black-box machine learning models in the context of rock discontinuity classification. The analysis reveals that features such as normal vectors, verticality, and Z-values have the greatest influence on identifying main discontinuity sets, while linearity, planarity, and eigenvalues contribute less, making the model more transparent and easier to understand. After classification, individual discontinuity sets were detected using a revised DBSCAN from the main discontinuity sets. Finally, the orientation parameters of the plane fitted to each discontinuity were derived from the plane parameters obtained using the Random Sample Consensus (RANSAC). Two real-world datasets (obtained from SfM and LiDAR) and one synthetic dataset were used to validate the proposed method, which successfully identified rock discontinuities and their orientation parameters (dip angle/direction).