Monitoring Of Roadway Surface Displacement Based On Close-Range Photogrammetry

It is one of the most important content of roadway support monitoring to monitor the surface displacement in roadway. And it also guarantees the safe production of coal mine.The main contents of the roadway surface displacement monitoringcontainthe floor convergence and the displacement of both sides. And there are two main methods to monitor the surface displacement of roadway, which are artificial regular monitoring and wired or wireless sensor monitoring. However, the project’s amount of artificial regular monitoring is relatively large. And the method has complicated measurement procedures and has inaccurate measurement accuracy.On the other hand, sensor monitoring has high cost, complex communication mechanism, and is easily influenced by the environment of coal mine roadway.To above-mentioned situations, close-range photogrammetry is applied to monitor the surface displacementof roadway in this paper.It mainly includes three partial contents:Construction of coal mine tunnel model. Firstly, according to the contents of the roadway surface displacement monitoring in coal mine, the laboratory model is built, and the whole project is collectivity planning.Extraction of object points in complex background. It is necessary to extract object points in complex background for as the environment in the coal mine roadway is complex and the object points placed are so small. Firstly, the histogram is used to do a simple image enhancement processing for the image. Then morphological filter of Top-hat transform is used to filter the image. And finally, an iterative method is used to obtain the optimal segmentation threshold of the image, which can be used to segment the image. As a result, the coordinates of object points can be extracted.Calculation of objects points’ coordinates. As the environment in coal mine roadway is dark, and the terrain is complex, it is no longer applicable to use the traditional camera calibration for the inner orientation elements of camera and the exterior orientation elements. As a result, the following method is used to obtain the internal and external camera parameters. At first, the same rectangle is taken photos for three times. And the geometric constrains of the rectangle is used to calibrate the camera. Then the interior orientation elements of the camera can be known. Next, according to the imaging relation of any plane in the space under the camera transformation, the homographic matrix can be determined. Finally, under the condition of mathematical constraints that is composed of homographic matrix, the exterior orientation elements of the camera can be obtained. After the internal and external parameters of the camera are obtained, the image coordinate of the object points can be converted into the world coordinate system. And after taking photos of the same section for some times at different times, the displacement of the roadway can be obtained.At last, the displacement of the object points in the roadway is measured by experiment in the laboratory. Experimental results show that the measurement error is less than 3.5% within the allowable error range,which proves that this subject is feasible.