A Long distance Image Measuring Technique for Crack on Tunnel Lining

Abstract:

According to its own characteristics of long distance taken image with cracks on tunnel lining， a new identification and width measuring algorithm for tunnel lining crack was developed by combining the calibration curve of camera fitted with experimental data, on the basis of some image processing means, such as image enhancement pre processing, region extraction of crack with loop iteration method, mathematical morphological analysis, edge detection of crack with sub pixel method. Verified by laboratory tests, when the shooting distance is less than 8 m, the algorithm is of high precision and the measurement error of crack width is generally less than 0.40 mm. According to its application, the maximum error of this algorithm is 0.37mm, the minimum error is 0.08mm, the average error is 0.20mm which meets the requirements of engineering measurement.

Key words:digital image processing;crack on tunnel lining;region extraction;sub pixel;edge detection;calibration method