A pipeline for structured light bathymetric mapping

Abstract

This paper details a methodology for using structured light laser imaging to create high resolution bathymetric maps of the sea floor. The system includes a pair of stereo cameras and an inclined 532nm sheet laser mounted to a remotely operated vehicle (ROV). While a structured light system generally requires a single camera, a stereo vision set up is used here for in-situ calibration of the laser system geometry by triangulating points on the laser line. This allows for quick calibration at the survey site and does not require precise jigs or a controlled environment. A batch procedure to extract the laser line from the images to sub-pixel accuracy is also presented. The method is robust to variations in image quality and moderate amounts of water column turbidity. The final maps are constructed using a reformulation of a previous bathymetric Simultaneous Localization and Mapping (SLAM) algorithm called incremental Smoothing and Mapping (iSAM). The iSAM framework is adapted from previous applications to perform sub-mapping, where segments of previously visited terrain are registered to create relative pose constraints. The resulting maps can be gridded at one centimeter and have significantly higher sample density than similar surveys using high frequency multibeam sonar or stereo vision. Results are presented for sample surveys at a submerged archaeological site and sea floor rock outcrop.

Generation of High‐resolution Three‐dimensional Reconstructions of the Seafloor in Color using a Single Camera and Structured Light

“…However, these methods suffer from difficulties of matching features in turbid water (Garcia & Gracias, 2011) and over terrain with few visual features, and they lead to variable resolution across the map as a function of the abundance of visual clues. Techniques for mapping bathymetry with consistently high resolution include different types of structured light by employing scanning point lasers (Kocak, Caimi, Das, & Karson, 1999;Moore, Jaffe, & Ochoa, 2000), line lasers (Inglis et al, 2012;Kondo et al, 2004;Tetlow & Spours, 1999), or light pattern projections (Bruno et al, 2011), which make use of the known relative positions of the camera and the projector. Measurements of the time of flight of a light impulse are used in LIDAR (Light Detection and Ranging) (Harsdorf et al, 1999) and serial imaging systems (Dalgleish et al, 2013).…”

“…While light sectioning using line lasers leads to regularly resolved shape reconstructions, it does not map any color information of the seafloor. Inglis et al presented a method (Inglis, Smart, Vaughn, & Roman, 2012) in which a bathymetry map generated from laser line scans is used to improve the accuracy of a stereo 3D reconstruction.…”

Exploring 3-D Reconstruction Techniques: A Benchmarking Tool for Underwater Robotics

“…Using the stereo camera, the 3D position of the pixels projected by the laser are obtained by triangulation. With those 3D points, The RANSAC algorithm is used to determine the planar parameters of the laser plane [19] ( c M l ). These parameters are referenced to the stereo camera using the previously obtained transformation between the camera and the end-effector ( c M e ), it is possible to reference the plane of the laser respect to it:…”

Submap bathymetric SLAM using structured light in underwater environments

“…Inglis et al [10] presented a structured light bathymetric mapping algorithm that accounts for errors in the horizontal component of the robot's position estimate.…”