Development of a portable device for structural visual inspection

Visual inspection is crucial for the maintenance of built infrastructures, facilitating early detection and quantification of damage. Traditional manual methods, however, often require inspectors to access dangerous or inaccessible areas, posing significant safety risks and inefficiencies. In response to these challenges, this paper introduces a portable visual inspection device (VID) integrated with three laser distance meters and a high-resolution camera. The VID enhances the efficiency of visual inspection by incorporating methods that accurately estimate the camera's pose relative to the target surface and determine a scale factor for precise damage quantification. The proposed methods were validated through experimental validations, demonstrating their precision and effectiveness. In lab-scale validation, the angle estimation showed accuracy with less than 3 degrees of error, and the scale factor estimation method showed discrepancies of less than 1 mm, even when the observation angle exceeded 20 degrees. Subsequent field experiments confirmed the VID's capability to detect and measure microcracks as narrow as 0.1 mm. Furthermore, the device successfully quantified non-crack damage with an error margin of 1.84%, even at challenging angles exceeding 45 degrees.