Fiducial markers for image alignment of surface texture measurements

Abstract Fiducial markers are widely used as reference for imaging systems across a range of different scientific disciplines, including applications like augmented reality, computer vision and medicine. This paper provides an introduction to the topic of fiducial markers, with an initial analysis of the state of the art with regard to their applications, characteristics and manufacturing processes across disciplines. Subsequently, the paper turns its attention to the utilisation of markers for the measurement of surface texture. As only a limited area of the surface is evaluated in comparison to the entire workpiece, it is necessary to use markings as a reference to relocate the measurement area. This paper presents two original solutions for applications related to surface texture measurement. The measurement is conducted using confocal microscopy. Initially, a combination of laser marking and height marker lines is proposed for the comparison of measurements obtained from different devices. Secondly, a novel approach to the safeguarding of markers throughout the manufacturing process is outlined, which employs the use of a bespoke 3D-printed cover. This methodology allows for the investigation of changes occurring at a specific location during manufacturing processes, thereby facilitating a more profound understanding of the impact of these processes. The examined markings serve as reference points for accurate relocation during measurement and data analysis. In all instances, digital image correlation was successfully performed. The design of the marker is unique and depends on the specific application, specimen, and imaging device. Despite the absence of a universal solution for fiducial markers, this study explores effective ways to utilise them and presents practical examples of their applications.