A Simple Device for Monitoring Cracks From Photographs

Abstract

Abstract. The article presents a simple technological solution PMC (PhotoMicrometer Contrast) for monitoring cracks and deformation joints in buildings and structures. The solution is based on the methods of image processing and photogrammetry. The monitoring equipment includes a special marker, a digital camera and specialized processing software. The marker consists of two thin plastic plates where Aruco marks and special measuring areas are printed. There are two types of markers – for monitoring in one or two directions of crack development. While monitoring is performed, two plates are fixed on both sides of the crack or deformation joint. Then the plates are photographed with a digital camera as often as the observation cycle requires. Any conventional modern digital camera is suitable for photographing after successfully passing the distortion effect test described in the article. Image processing in the software includes automatic identification of the marker in the image, binarization of the image, determination of its scale and dimensions of measuring areas in the current observation cycle. For processing images made at large angles of inclination and rotation, a preliminary solution of the resection in space and the images rectification to the found angles is provided. The dynamics of crack development is determined by the results of several cycles of observations collected over period. Our technology ensures the accuracy of the determination of coordinates and deformations at the level of 0.05 mm and higher for photographing distances from 0.3 to 50 m.