Online Refractive Camera Model Calibration in Visual Inertial Odometry

TL;DR

This paper introduces an online calibration method for visual-inertial odometry that estimates the refractive index of unknown media, enabling accurate operation in diverse fluids without prior calibration.

Contribution

It proposes a novel refractive camera model and online estimation of the refractive index within a visual-inertial odometry framework, adaptable to various refractive media.

Findings

Converges to the true refractive index of water despite initialization errors.

Maintains odometry performance in refractive media without prior medium-specific calibration.

Validated on underwater robot data in a pool environment.

Abstract

This paper presents a general refractive camera model and online co-estimation of odometry and the refractive index of unknown media. This enables operation in diverse and varying refractive fluids, given only the camera calibration in air. The refractive index is estimated online as a state variable of a monocular visual-inertial odometry framework in an iterative formulation using the proposed camera model. The method was verified on data collected using an underwater robot traversing inside a pool. The evaluations demonstrate convergence to the ideal refractive index for water despite significant perturbations in the initialization. Simultaneously, the approach enables on-par visual-inertial odometry performance in refractive media without prior knowledge of the refractive index or requirement of medium-specific camera calibration.