Automatic tiny crack positioning and width measurement with parallel laser line-camera system

Abstract

Quantifying tiny cracks is crucial for assessing structural conditions. Traditional non-contact measurement technologies often struggle to accurately measure tiny crack widths, especially in hard-to-access areas. To address these challenges, this study introduces an image-based, handheld parallel laser line-camera (PLLC) system designed for automated tiny crack localization and width measurement from multiple angles and safe distances. Established by processing parallel laser strips, the camera coordinate system addresses crack positioning and pixel scale distortion challenges typical in non-perpendicular photography. The determined pixel scale enables accurate width measurement. An improved U-Net model automatically identifies crack pixels, enhancing detection accuracy. Additionally, the newly developed Equal Area algorithm enables the sub-pixel width measurement of tiny cracks. Comprehensive laboratory and field testing demonstrates the system's accuracy and feasibility across various conditions. This PLLC system achieves quantitative tiny crack detection in one shot, significantly enhancing the efficiency and utility of on-site inspections.