T-CoLoc: Leveraging Tethers for Reliable Co-Localization within an Underwater ROV Chain
Juliette Drupt, Claire Dune, Andrew Ian Comport, Vincent Hugel
AI summary
Problem
Aligning multi-robot localization and mapping in unknown underwater environments is hindered by poor visual conditions, acoustic interference, and frequent VSLAM resets that break map continuity.
Approach
The method leverages a coarse estimate of the physical tether's shape between two robots to mathematically align their individual VSLAM outputs into a common reference frame via on-manifold optimization.
Key results
- Sub-20 cm alignment error for a 3 m tether using noisy shape estimates
- Up to 3x and 10x error reduction in translation and orientation versus direct tether estimates
- Successful realignment of disconnected SLAM trajectories after simulated resets
- Reliable inter-robot pose estimation without visual place recognition
Why it matters
It enables robust cooperative navigation and mapping for underwater robot chains in turbid or feature-poor environments where traditional visual matching fails.
Abstract
Underwater Remotely Operated Vehicles (ROVs) exchange data with a control station via a communication cable. One or more intermediate robots can be placed along this tether to manage its shape and minimize the mechanical effects on the ROV. This work deals with the localization of a pair of underwater robots connected by a tether, in a previously unknown environment. While each robot can estimate its trajectory and a model of its surroundings using Simultaneous Localization And Mapping (SLAM) algorithms, aligning these observations in the same reference frame requires inter-robot data association. In this work, we introduce T-Coloc, a new method for aligning models’ frames that leverages an estimation of the tether shape to align individual robot observations. An experimental validation in a pool demonstrates that T-CoLoc can align the trajectories of the two robots in the same reference frame with an error lower than 20 cm using the noisy shape estimation of a 3 m long tether.