Non-Contact Concrete Crack Measurement Methodology Based On Monocular Vision

In recent years,the detection of concrete cracks by digital image technology has made much progress,and the research on the recognition of concrete cracks rises to a new level.The traditional damage detection method is time-consuming and needs lots of human resources.Therefore,this paper proposed a new automatic and non-contact method and a standard operating process of the concrete crack measurement.The research used the image processing technology and computer vision technology.This paper conducted three simulation experiments and one practical and real experiments and the results verified the feasibility and effectiveness of the method and process.Firstly,this paper systematically overthrew the principle from binocular vision measurement to monocular vision measurement,and established a complete concrete crack measurement framework.These works provided sufficient theoretical basis for the next simulation and practical experiments.In addition,the method of extracting pixel points based on digital image was studied in detail,and the Harris algorithm was used to detect the corner points.Then the sub-pixel corner point extraction method was used to increases the extraction precision of corner point.Secondly,this paper conducted three simulation experiments and a practical concrete experiment.The parameters of first simulation experiment were the shooting angle,shooting distance and the location of the chessboard in the image and the purpose the experiment was to explore the influence on measurement accuracy.The result of the first experiment found that the parallel camera,closed shooting distance and the central chessboard is the positive factors of the high measurement accuracy;The second experiment mainly explores how the the accuracy of the target size influenced the accuracy of the measured coordinate.The results found that well-made customized chessboard can obtain better measurement results than roughly printed chessboard.The third experiment aimed to determine the effective distance from the camera to the chessboard and explored how different size of the chessboard influenced the accuracy of the crack measurement The results found that the effective shooting distance were 2 m and 1 m,and the bigger cheboard could make the higheraccuracy;And the last concrete measurement experiment was conducted successfully and the results showed the error rate of the width of the crack was small.It proved that the automatic measuring method and measuring process is feasible and effective.