Joint mapping automation
Originally published in the Tenth International Mining Geology Conference 2017 Proceedings, this paper reviews automated joint mapping techniques using the concentric shells algorithm.
Automated joint mapping using the concentric shells algorithm
By P. Valenzuela, MAusIMM, CP Geotech, Senior Geotechnical Engineer. Rox-Ray
A routine task conducted by geologists and geotechnical engineers is to map rock faces, and identify and record relevant structures such as faults, joints, foliations, etc. This task is a major input in engineering/geology analyses. Depending on the reason to map, personnel may concentrate more on structures controlling the stability of an excavation (typically faults and joints) or in features controlling ore mineralisation (e.g. bedding). One of the basic properties to map from structures are orientation angles: dip and dip direction. This has been done traditionally using a compass in the field.
In order to facilitate and speed up joint mapping, new techniques have been developed that allow to scan a rock face and produce a point cloud (e.g. laser scanning and photogrammetry). The point cloud is then loaded onto a screen and the user must identify and delineate structures visually. This is a lengthy process that can take hours or days. A method to identify joints automatically on a point cloud is presented in this paper. It is called the Concentric Shells Algorithm. The method scans a point cloud sequentially, tests if selected points are ‘true pivots’ within an inner shell, and then it searches for points inside a larger sphere (outer shell). After a series of pivots are found then they are amalgamated and assembled to return the estimated joints. The algorithm has been applied and validated on a number of sites (open pits) and simulated datasets. The usual running times are up to 4-5 minutes, which reduces significantly the time spent doing mapping on the screen or in the field. The algorithm is flexible to read point clouds/scans captured by any scanner or total station. Estimated joints can readily be imported into mining software packages and used in pit optimization and design.
Automated joint mapping tool
Deswik.JF (Joint Finder) is an automation tool which uses the concentric shells algorithm. It automates joint mapping from the scan of a rock face. The user enters a point cloud file (3D coordinates) and input parameters, and Deswik.JF delineates the estimated joints on the wall. Deswik.JF uses the concentric shells algorithm to outline pivots, and post-processing modules to amalgamate and assemble the joints. For more information, go to this page or download this flyer.