ReAqROVIO: Refractive Aquatic ROVIO

This repository contains the implementation of the work Online refractive camera model calibration in visual-inertial odometry. The method enables Visual-Inertial Odometry (VIO) underwater without the need of camera calibration in the water. The cameras are only calirated in air and the refractive distortion due to water is rectified online by estimating the refractive index in the state of the Iterated Extended Kalman Filter. The work is developed over ROVIO.

Paper:

• https://doi.org/10.48550/arXiv.2409.12074 (IROS 2024)

Key features:

1. Refractive camera model: to enable online adaptation of the camera model to mitigate the refractive effects of underwater given the calibration in air.
2. Barometric Depth Update: Integration of barometric depth update.
3. Multi-camera: Extending unified refractive index estimation with odometry from multiple synchronized cameras.

Multi-Camera Underwater Dataset

ReAqROVIO can be tested on our open-source Multi Camera Underwater Visual-Inertial Dataset. We use the 3rd subset of the dataset for our experiments in this work.

YouTube Video

Installation

Dependencies

• ros1
  • Tested on ros noetic
• kindr (https://github.com/ethz-asl/kindr)
  • Clone outside rovio ros package, within the same workspace
• lightweight_filtering (clone from lightweight_filtering or, as submodule, use "git submodule update --init --recursive")
  • Clone inside rovio ros package

Install without opengl scene (recommended)

#!build

catkin build rovio --cmake-args -DCMAKE_BUILD_TYPE=Release

If the CMakeList is updated, then, clean and rebuild as follows:

#! re-build
catkin clean rovio
catkin build rovio --cmake-args -DCMAKE_BUILD_TYPE=Release

Install with opengl scene

Additional dependencies: opengl, glut, glew (sudo apt-get install freeglut3-dev, sudo apt-get install libglew-dev)

#!command

catkin build rovio --cmake-args -DCMAKE_BUILD_TYPE=Release -DMAKE_SCENE=ON

Usage instructions

Rosbag download and play

1. Download rosbags for trajectory (eg. Traj 1 from the dataset link)
2. Move all the bag rosbag files into a directory (eg. <path to dataset>/Traj1)
3. Play the rosbag for either monocular or stereo configuration:

# Mono: (i.e setting ROVIO_NCAM to 1 in CMakeList):
 
rosbag play <path to dataset>/Traj1/* --topics /alphasense_driver_ros/cam0 /alphasense_driver_ros/imu --clock

# Stereo: (i.e setting ROVIO_NCAM to 2 in CMakeList):

rosbag play <path to dataset>/Traj1/* --topics /alphasense_driver_ros/cam0 /alphasense_driver_ros/cam1 /alphasense_driver_ros/imu --clock

Setting ROVIO parameters

CMakeList

The CMakeList controls the maximum number of features used in the state of ROVIO, the number of cameras used and multi-level patch parameters. ** Parameters**

set(ROVIO_NMAXFEATURE 25 CACHE STRING "Number of features for ROVIO")
set(ROVIO_NCAM 2 CACHE STRING "Number of enabled cameras")

Launch file

The launch file allows to set the initialization for the refractive index

refractive_index = 1.33 (ideal value for fresh water)

info file

To enable to estimation of refractive index online, set following parameters as true, if false, the above initialization is used as a constant value.

refractiveCalibration true 
useObservabilityCheck true

To tune the convergence of the refractive index, following noise parameter can be varied.

Prediction.PredictionNoise.ref_0 2.0e-6;

Running Launch file

• Terminal 1

roslaunch rovio sim_core.launch

• Terminal 2

rosbag play <path to dataset>/Traj1/* --topics /alphasense_driver_ros/cam0 /alphasense_driver_ros/cam1 /alphasense_driver_ros/imu --clock

• Terminal 3

roslaunch rovio rovio_rcm.launch

Potential issues and fixes

• In case git submodule update fails please clone git@github.com:Mohit505Git/lightweight_filtering.git in the lightweight_filter directory.
• If any incorrect syntax is present in the .info file, then this leads to formation of a default new info file as .info_new and rovio may fail. Delete the .info_new file and retry with correct syntax.
• Continous synchronization failed error may arise due to mismatch in the topics played from the rosbag file and number or camera set in the CMakeList.

Further notes

• Camera matrix and distortion parameters should be provided by a yaml file or loaded through rosparam
• The cfg/rovio.info provides most parameters for rovio. The camera extrinsics qCM (quaternion from IMU to camera frame, Hamilton-convention) and MrMC (Translation between IMU and Camera expressed in the IMU frame) should also be set there. They are being estimated during runtime so only a rough guess should be sufficient.
• Especially for application with little motion fixing the IMU-camera extrinsics can be beneficial. This can be done by setting the parameter doVECalibration to false. Please be carefull that the overall robustness and accuracy can be very sensitive to bad extrinsic calibrations.

Papers reference for ROVIO:

• http://dx.doi.org/10.3929/ethz-a-010566547 (IROS 2015)
• http://dx.doi.org/10.1177/0278364917728574 (IJRR 2017)

Reference

If you use ReAqROVIO in your research, please cite our work!

@article{singh2024online,
      title={Online Refractive Camera Model Calibration in Visual Inertial Odometry},
      author={Singh, Mohit and Alexis, Kostas},
      journal={arXiv preprint arXiv:2409.12074},
      year={2024}
    }

Contact

You can contact us for any question or feel free to post an issue on this repository:

• Mohit Singh
• Kostas Alexis