Spiral trajectory planning approach for underground cavity measurements based on laser scanning

Underground cavity three-dimensional measurements constitute an important and challenging task in underground mining. The laser scanning method is a relatively precise and efficient way to address this problem, but it is limited by the unevenness of the point cloud that reduces the scanning efficiency. In this paper, an approach that can increase the evenness of the point cloud in underground laser scanning is proposed. The approach is based on a spiral trajectory planning strategy. The scanning trajectory is generated from previous scan by solid geometry. Exceptions are discussed and solutions are proposed. The approach was used in an actual laser scanning system and experiments were carried out in a gold mine in Hebei Province, North China. To assess the results, 3D Delaunay triangulation network of laser points was built in accordance to a semispherical-planer projection rule, and the area of each triangle in the network was calculated. The coefficient of variance of the triangular area indicated that the new approach can increase the evenness of the laser points efficiently.