注释以及修改

Related Works and Extended Application

SLAM:

1. ikd-Tree: A state-of-art dynamic KD-Tree for 3D kNN search.
2. R2LIVE: A high-precision LiDAR-inertial-Vision fusion work using FAST-LIO as LiDAR-inertial front-end.
3. LI_Init: A robust, real-time LiDAR-IMU extrinsic initialization and synchronization package..
4. FAST-LIO-LOCALIZATION: The integration of FAST-LIO with Re-localization function module.

Control and Plan:

1. IKFOM: A Toolbox for fast and high-precision on-manifold Kalman filter.
2. UAV Avoiding Dynamic Obstacles: One of the implementation of FAST-LIO in robot's planning.
3. UGV Demo: Model Predictive Control for Trajectory Tracking on Differentiable Manifolds.
4. Bubble Planner: Planning High-speed Smooth Quadrotor Trajectories using Receding Corridors.

FAST-LIO

FAST-LIO (Fast LiDAR-Inertial Odometry) is a computationally efficient and robust LiDAR-inertial odometry package. It fuses LiDAR feature points with IMU data using a tightly-coupled iterated extended Kalman filter to allow robust navigation in fast-motion, noisy or cluttered environments where degeneration occurs. Our package address many key issues:

1. Fast iterated Kalman filter for odometry optimization;
2. Automaticaly initialized at most steady environments;
3. Parallel KD-Tree Search to decrease the computation;

FAST-LIO 2.0 (2021-07-05 Update)

Related video: FAST-LIO2, FAST-LIO1

Pipeline:

New Features:

1. Incremental mapping using ikd-Tree, achieve faster speed and over 100Hz LiDAR rate.
2. Direct odometry (scan to map) on Raw LiDAR points (feature extraction can be disabled), achieving better accuracy.
3. Since no requirements for feature extraction, FAST-LIO2 can support many types of LiDAR including spinning (Velodyne, Ouster) and solid-state (Livox Avia, Horizon, MID-70) LiDARs, and can be easily extended to support more LiDARs.
4. Support external IMU.
5. Support ARM-based platforms including Khadas VIM3, Nivida TX2, Raspberry Pi 4B(8G RAM).

Related papers:

FAST-LIO2: Fast Direct LiDAR-inertial Odometry

FAST-LIO: A Fast, Robust LiDAR-inertial Odometry Package by Tightly-Coupled Iterated Kalman Filter

Contributors

Wei Xu 徐威，Yixi Cai 蔡逸熙，Dongjiao He 贺东娇，Fangcheng Zhu 朱方程，Jiarong Lin 林家荣，Zheng Liu 刘政, Borong Yuan

1. Prerequisites

1.1 Ubuntu and ROS

Ubuntu >= 16.04

For Ubuntu 18.04 or higher, the default PCL and Eigen is enough for FAST-LIO to work normally.

ROS >= Melodic. ROS Installation

1.2. PCL && Eigen

PCL >= 1.8, Follow PCL Installation.

Eigen >= 3.3.4, Follow Eigen Installation.

1.3. livox_ros_driver

Follow livox_ros_driver Installation.

Remarks:

• Since the FAST-LIO must support Livox serials LiDAR firstly, so the livox_ros_driver must be installed and sourced before run any FAST-LIO luanch file.
• How to source? The easiest way is add the line source $Livox_ros_driver_dir$/devel/setup.bash to the end of file ~/.bashrc, where $Livox_ros_driver_dir$ is the directory of the livox ros driver workspace (should be the ws_livox directory if you completely followed the livox official document).

2. Build

Clone the repository and catkin_make:

    cd ~/$A_ROS_DIR$/src
    git clone https://github.com/hku-mars/FAST_LIO.git
    cd FAST_LIO
    git submodule update --init
    cd ../..
    catkin_make
    source devel/setup.bash

• Remember to source the livox_ros_driver before build (follow 1.3 livox_ros_driver)
• If you want to use a custom build of PCL, add the following line to ~/.bashrc export PCL_ROOT={CUSTOM_PCL_PATH}

3. Directly run

Noted:

A. Please make sure the IMU and LiDAR are Synchronized, that's important.

B. The warning message "Failed to find match for field 'time'." means the timestamps of each LiDAR points are missed in the rosbag file. That is important for the forward propagation and backwark propagation.

C. We recommend to set the extrinsic_est_en to false if the extrinsic is give. As for the extrinsic initiallization, please refer to our recent work: Robust Real-time LiDAR-inertial Initialization.

3.1 For Avia

Connect to your PC to Livox Avia LiDAR by following Livox-ros-driver installation, then

    cd ~/$FAST_LIO_ROS_DIR$
    source devel/setup.bash
    roslaunch fast_lio mapping_avia.launch
    roslaunch livox_ros_driver livox_lidar_msg.launch

• For livox serials, FAST-LIO only support the data collected by the livox_lidar_msg.launch since only its livox_ros_driver/CustomMsg data structure produces the timestamp of each LiDAR point which is very important for the motion undistortion. livox_lidar.launch can not produce it right now.
• If you want to change the frame rate, please modify the publish_freq parameter in the livox_lidar_msg.launch of Livox-ros-driver before make the livox_ros_driver pakage.

3.2 For Livox serials with external IMU

mapping_avia.launch theratically supports mid-70, mid-40 or other livox serial LiDAR, but need to setup some parameters befor run:

Edit config/avia.yaml to set the below parameters:

1. LiDAR point cloud topic name: lid_topic
2. IMU topic name: imu_topic
3. Translational extrinsic: extrinsic_T
4. Rotational extrinsic: extrinsic_R (only support rotation matrix)

• The extrinsic parameters in FAST-LIO is defined as the LiDAR's pose (position and rotation matrix) in IMU body frame (i.e. the IMU is the base frame). They can be found in the official manual.
• FAST-LIO produces a very simple software time sync for livox LiDAR, set parameter time_sync_en to ture to turn on. But turn on ONLY IF external time synchronization is really not possible, since the software time sync cannot make sure accuracy.

3.3 For Velodyne or Ouster (Velodyne as an example)

Step A: Setup before run

Edit config/velodyne.yaml to set the below parameters:

1. LiDAR point cloud topic name: lid_topic
2. IMU topic name: imu_topic (both internal and external, 6-aixes or 9-axies are fine)
3. Set the parameter timestamp_unit based on the unit of time (Velodyne) or t (Ouster) field in PoindCloud2 rostopic
4. Line number (we tested 16, 32 and 64 line, but not tested 128 or above): scan_line
5. Translational extrinsic: extrinsic_T
6. Rotational extrinsic: extrinsic_R (only support rotation matrix)

• The extrinsic parameters in FAST-LIO is defined as the LiDAR's pose (position and rotation matrix) in IMU body frame (i.e. the IMU is the base frame).

Step B: Run below

    cd ~/$FAST_LIO_ROS_DIR$
    source devel/setup.bash
    roslaunch fast_lio mapping_velodyne.launch

Step C: Run LiDAR's ros driver or play rosbag.

3.4 PCD file save

Set pcd_save_enable in launchfile to 1. All the scans (in global frame) will be accumulated and saved to the file FAST_LIO/PCD/scans.pcd after the FAST-LIO is terminated. pcl_viewer scans.pcd can visualize the point clouds.

Tips for pcl_viewer:

• change what to visualize/color by pressing keyboard 1,2,3,4,5 when pcl_viewer is running.

    1 is all random
    2 is X values
    3 is Y values
    4 is Z values
    5 is intensity

4. Rosbag Example

4.1 Livox Avia Rosbag

Files: Can be downloaded from google drive

Run:

roslaunch fast_lio mapping_avia.launch
rosbag play YOUR_DOWNLOADED.bag

4.2 Velodyne HDL-32E Rosbag

NCLT Dataset: Original bin file can be found here.

We produce Rosbag Files and a python script to generate Rosbag files: python3 sensordata_to_rosbag_fastlio.py bin_file_dir bag_name.bag

Run:

roslaunch fast_lio mapping_velodyne.launch
rosbag play YOUR_DOWNLOADED.bag

5.Implementation on UAV

In order to validate the robustness and computational efficiency of FAST-LIO in actual mobile robots, we build a small-scale quadrotor which can carry a Livox Avia LiDAR with 70 degree FoV and a DJI Manifold 2-C onboard computer with a 1.8 GHz Intel i7-8550U CPU and 8 G RAM, as shown in below.

The main structure of this UAV is 3d printed (Aluminum or PLA), the .stl file will be open-sourced in the future.

6.Acknowledgments

Thanks for LOAM(J. Zhang and S. Singh. LOAM: Lidar Odometry and Mapping in Real-time), Livox_Mapping, LINS and Loam_Livox.