Abstract
<p>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.<br>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.</p>