msckf_vio/README.md

MSCKF_VIO

The MSCKF_VIO package is a stereo version of MSCKF. The software takes in synchronized stereo images and IMU messages and generates real-time 6DOF pose estimation of the IMU frame.

The software is tested on Ubuntu 16.04 with ROS Kinetic.

Video: https://www.youtube.com/watch?v=jxfJFgzmNSw&t=3s Paper Draft: https://arxiv.org/abs/1712.00036

License

Penn Software License. See LICENSE.txt for further details.

Dependencies

Most of the dependencies are standard including Eigen, OpenCV, and Boost. The standard shipment from Ubuntu 16.04 and ROS Kinetic works fine. One special requirement is suitesparse, which can be installed through,

sudo apt-get install libsuitesparse-dev

Compling

The software is a standard catkin package. Make sure the package is on ROS_PACKAGE_PATH after cloning the package to your workspace. And the normal procedure for compiling a catkin package should work.

cd your_work_space
catkin_make --pkg msckf_vio --cmake-args -DCMAKE_BUILD_TYPE=Release

Calibration

An accurate calibration is crucial for successfully running the software. To get the best performance of the software, the stereo cameras and IMU should be hardware synchronized. Note that for the stereo calibration, which includes the camera intrinsics, distortion, and extrinsics between the two cameras, you have to use a calibration software. Manually setting these parameters will not be accurate enough. Kalibr can be used for the stereo calibration and also to get the transformation between the stereo cameras and IMU. The yaml file generated by Kalibr can be directly used in this software. See calibration files in the config folder for details. The two calibration files in the config folder should work directly with the EuRoC and fast flight datasets. The convention of the calibration file is as follows:

camx/T_cam_imu: takes a vector from the IMU frame to the camx frame. cam1/T_cn_cnm1: takes a vector from the cam0 frame to the cam1 frame.

The filter uses the first 200 IMU messages to initialize the gyro bias, acc bias, and initial orientation. Therefore, the robot is required to start from a stationary state in order to initialize the VIO successfully.

EuRoC and UPenn Fast flight dataset example usage

Once the msckf_vio is built and sourced (via source <path to catkin_ws>/devel/setup.bash), there are two launch files prepared for the EuRoC and UPenn fast flight dataset with launch files msckf_vio_euroc.launch and msckf_vio_fla.launch respectively. The launch files instanciates two ROS nodes:

• image_processor processes stereo images to detect and track features
• vio obtains feature measurements from the image_processor and tightly fuses them with the IMU messages to estimate pose.

These launch files can be executed via

roslaunch msckf_vio msckf_vio_euroc.launch

or 

roslaunch msckf_vio msckf_vio_fla.launch

Once the nodes are running you need to run the dataset rosbags, for example:

rosbag play V1_01_easy.bag

As mentioned in the previous section The robot is required to start from a stationary state in order to initialize the VIO successfully

To visualize the pose and feature estimations you can use the provided rviz configurations found in msckf_vio/rviz folder to visualize corresponding datatset estimations (EuRoC: rviz_euroc_config.rviz, Fast dataset: rvis_fla_config.rviz).

ROS Nodes

image_processor node

Subscribed Topics

imu (sensor_msgs/Imu)

IMU messages is used for compensating rotation in feature tracking, and 2-point RANSAC.

cam[x]_image (sensor_msgs/Image)

Synchronized stereo images.

Published Topics

features (msckf_vio/CameraMeasurement)

Records the feature measurements on the current stereo image pair.

tracking_info (msckf_vio/TrackingInfo)

Records the feature tracking status for debugging purpose.

debug_stereo_img (sensor_msgs::Image)

Draw current features on the stereo images for debugging purpose. Note that this debugging image is only generated upon subscription.

vio node

Subscribed Topics

imu (sensor_msgs/Imu)

IMU measurements.

features (msckf_vio/CameraMeasurement)

Stereo feature measurements from the image_processor node.

Published Topics

odom (nav_msgs/Odometry)

Odometry of the IMU frame including a proper covariance.

feature_point_cloud (sensor_msgs/PointCloud2)

Shows current features in the map which is used for estimation.