Towards automated laser triangulation with stereo and planar constraints in refractive environments

This paper presents two automated correspondence-search algorithms for stereo laser triangulation in multimedia (refractive) environments, enforcing coplanarity through forward ray tracing without iterative back-projection. By shifting computations from image to object space, the methods directly minimize either the skew distance between refracted rays or the distance between their intersections with a laser plane, yielding strict refractive geometry within a single optimization loop. The methods are validated on an automated wood conservation monitoring system, where a stereo camera system with a line laser operates over a water-filled conservation tank. This application provides the environment for both algorithmic efficiency and accuracy requirements, demanding sub-millimeter precision over extended monitoring periods. Both algorithms reconstruct timber structures with high quality with the added planar constraint substantially reducing noise and edge outliers while slightly lowering point density. Water-surface estimation achieves plane-fit RMS of about 0.2 mm with a similar ground sample distance (GSD) and agrees with independent ruler measurements within 2 mm, enabling water-level monitoring over 14 epochs and cross-validation with calibration-derived plane parameters. Reference measurements on a 230 × 230 mm plane and three 50 mm spheres yield sub-millimeter residuals, with the plane constraint providing higher precision and fewer outliers. Finally, the computational efficiency is evaluated, showing favorable results for one of the algorithms compared to a standard procedure for correspondence search. Results demonstrate efficient, accurate, and transferable stereo laser triangulation through water and straightforward extensibility to multi-camera systems or non-perpendicular laser–water incidence angles. • Two novel correspondence search approaches for refractive stereo laser triangulation. • Application of the approaches on an automated wood conservation monitoring system. • Evaluation of the proposed approach against reference shapes. • Measurement of water planes with a stereo laser triangulation system. • Validation of water plane parameters with independent measurements.