Remote Pipe Diameter Measurement from a single Image using Laser Scale Projectionwith a Depth Compensation Model

Alice Weza Fava Bilbáo, Leonardo Sales Galvão, DANIEL JUCHEM REGNER, Moacir Wendhausen, Gierri Waltrich, Carla Alves Marinho Ferreira, TIAGO LOUREIRO FIGARO DA COSTA PINTO

Abstract. The dimensional measurement of cylindrical components, such as pipes, is a critical demand for quality control in industrial inspection. Monocular (single-view) computer vision-based approaches offer a low-cost and highly flexible solution but face the fundamental challenge of scale ambiguity. This paper proposes a method for measuring pipe diameter that solves this ambiguity by utilizing the projection of two laser points onto the object from the beam-splitting of a single laser source. The system projects two points with a known and previously calibrated distance onto the object's surface, providing the necessary scale information (mm/pixel) for the image. However, the projection onto the curved surface of the pipe induces a systematic error, as the laser dots land at a different depth (Z) than the depth of the apparent edges of the diameter in the 2D image. The main contribution of this work is the development and validation of a curvature compensation algorithm that mathematically corrects this depth distortion. Experimental results demonstrate that the proposed method, by compensating for the curvature, enables precise diameter measurement with a simple monocular system. For a pipe with a nominal diameter of 165 mm, measured at 6 m distance, the bias in the estimated diameter was reduced from 1.5% to less than 0.2%.