Spatial measurement of deformation (underground/ opencast) using automatic target recognition system
The complicated deformation model of a coal mining face comprises a number of parameters but, generally, the deformation study of hanging and side walls is used to assess the stability of the mining structure. The strata of the immediate roof undergoes vertical loading and, generally, remains in tension. Under the gravitational loading these roof strata try to converge with the floor despite the natural strength of the strata. Here a measuring system has to be remote, portable, fast, robust and accurate. For this purpose a Leica Automatic Target Recognition Total Station (Leica TDA 5005) is procured under modernization scheme of CSIR. This proved to be one of the best system for the deformation monitoring of inaccessible objects and even worked effectively in the underground envoronment.
R& D work is also conducted for automatic close range photogrammetric measurements as this is of immense importance for a hazardous industry like mining. Unfortunately available stereomatching techniques fail for high resolution close range images due to the large variation of object depth. In this paper a diffraction grating based laser dot-matrix projector along with a CCD camera is used for automatic close range measurement of a textureless and featureless object like massive sand stone strata. Targeting of object’s surface with large number of laser dots simultaneously solved two major problems: identification of conjugate points and precise image co-ordinate measurement. Least squares based template matching is used for centroid location of images of laser dots which provided 0.03 (mean) pixels accuracy. Using analytical techniques, camera model of the projector was developed by placing it rigidly on the telescope of a geodimeter. Bundle adjustment procedure is adopted for accurate estimation of interior orientation parameters of the projector which resulted precise co-ordinates of the object space during a test scan by the developed system.
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[1] Sheorey, P. R., Das, M. N., Barat, D., Prasad, R. K. and Singh, B., 1987. Coal pillar strength estimation from failed and stable cases. International Journal of Rock mechanics and Mining Sciences, 24: 347-355.