Towards Reliable Crack Growth Monitoring: A Preliminary Study on Fiducial Marker-Based Camera Repositioning Errors

This study explores the precision and practical feasibility of using fiducial markers and projective transformations for non-contact displacement measurement in structural monitoring applications. By tracking a grid of ArUco markers affixed to a planar surface, image alignment was achieved using homography-based rectification, enabling subpixel accuracy in displacement and strain evaluation. A high-resolution industrial camera setup with calibrated optics and image averaging was used to minimize noise. The impact of camera repositioning errors - translational and rotational – on displacement accuracy was systematically evaluated through three controlled scenarios. Results show that while minor displacements (e.g., 5 mm shifts) can introduce errors up to hundreds of micrometres, careful alignment and the use of projective correction significantly reduce this effect. The findings highlight both the promise and the limitations of this low-cost, repeatable approach, especially for applications such as crack monitoring, where high spatial precision is required.