Stereo vision based swing angle sensor for mining rope shovel

An easily retrofittable stereo vision based system for quick and temporary measurement of a mining shovel´s swing angle is presented. The stereo camera is mounted externally to the upper swingable shovel house, with a clear view of the shovel´s lower carbody. As the shovel swings from its 0° swing angle position, the camera revolves with the shovel house, seeing differing views of the carbody. In real-time, the camera position is tracked, which in turn is used to calculate the swing angle. The problem was solved using the Simultaneous Localization and Mapping (SLAM) approach in which the system learns a map of 3D features on the carbody while using the map to determine the camera pose. The contribution includes a locally maximal Harris corner selection technique and a novel use of 3D feature clusters as landmarks, for improving the robustness of visual landmark matching in an outdoor environment. Results show that the vision-based sensor has a maximum error of +/- 1° upon map convergence.