Macro-photogrammetry as a tool for the accurate measurement of three-dimensional misalignment in welding

Misalignment in welding presents several problems for the integrity of structures and machines. For this reason, the measurement of misalignment is relevant for the correct evaluation of quality in welds. This paper presents a new low-cost procedure based on photographic images acquired with a non-professional camera. The procedure consists on the application of macro-photogrammetry for the generation of a three-dimensional point cloud from the images. Subsequently a mathematical processing based on Principal Component Analysis (PCA) is applied to the generated point cloud in order to fit a plane to each welded plaque. The evaluation of the orientation between fitted planes allows the accurate measurement of the angle of misalignment for the welded union. The method is validated by the comparison of the results with those obtained with the metrological techniques.