emcl2_ros2: mcl with expansion resetting (version 2)

Emcl is an alternative Monte Carlo localization (MCL) package to amcl (http://wiki.ros.org/amcl). Differently from amcl, KLD-sampling and adaptive MCL are not implemented. Instead, the expansion resetting and other features are implemented¹².

This package is ROS 2 version of ryuichiueda/emcl2.

ROS 2 version

• ROS 2 Humble Hawksbill

quick start

Install & Build

mkdir ros2_ws && cd ros2_ws
git clone git@github.com:CIT-Autonomous-Robot-Lab/emcl2_ros2.git ./src/emcl2_ros2
rosdep update
rosdep install -y --from-paths src --ignore-src --rosdistro $ROS_DISTRO
sudo apt install -y ros-$ROS_DISTRO-navigation2 ros-$ROS_DISTRO-nav2-bringup ros-$ROS_DISTRO-turtlebot3-gazebo
colcon build --symlink-install --cmake-args -DCMAKE_BUILD_TYPE=Release
source install/setup.bash

Try emcl2 in simulator

You may wait Gazebo to be initilalized. You can also use ./test/demo.bash, in which the following procedure is written.

export TURTLEBOT3_MODEL=burger
ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py
ros2 launch nav2_bringup rviz_launch.py
ros2 launch emcl2 emcl2.launch.py params_file:=$(ros2 pkg prefix --share emcl2)/config/emcl2_quick_start.param.yaml map:=$(ros2 pkg prefix --share nav2_bringup)/maps/turtlebot3_world.yaml use_sim_time:=true
ros2 launch nav2_bringup navigation_launch.py use_sim_time:=true

demo movies

Nodes

emcl2_node

This node calculates the alpha value with a different algorithm than emcl_node in ryuichiueda/emcl. This node counts the particles that make lasers penetrate occupancy cells. Specifically, this node chooses some particles at a rate of extraction_rate and checks each of them with the following procedure:

• maps a set of laser scan on the occupancy grid map based on the pose of the particle
• judges the pose of the particle as wrong if all of lasers in a range_threshold[rad] range penatrate occupancy grids

If the rate of the wrong particles is greater than alpha_threshold, the node invokes a reset.

This node also has a sensor resetting algorithm. When sensor_reset is true, a particle with laser penetration is dragged back from occupied cells.

Subscribed Topics

Name	Type	Description
map	nav_msgs/OccupancyGrid	occupancy grid map
scan	sensor_msgs/LaserScan	laser scans
tf	tf/tfMessage	transforms
initialpose	geometry_msgs/PoseWithCovarianceStamped	pose of particles for replacement

Published Topics

Name	Type	Description
mcl_pose	geometry_msgs/PoseWithCovarianceStamped	the mean pose of the particles with covariance
particlecloud	geometry_msgs/PoseArray	poses of the particles
tf	tf/tfMessage	the transform from odom (which can be remapped via the odom_frame_id parameter) to map
alpha	std_msgs/Float32	marginal likelihood of particles after sensor update

Parameters

Name	Type	Default	Description
odom_freq	int	20 [Hz]	frequency of odometry update
num_particles	int	500	number of particles
odom_frame_id	string	"odom"	the frame for odometry
footprint_frame_id	string	"base_footprint"	the frame of the localized robot's base
base_frame_id	string	"base_link"	the frame of the robot's base. It is used for calculating the position and orientation of the LiDAR
global_frame_id	string	"map"	the frame for localization
initial_pose_x	double	0.0 [m]	initial x coordinate of particles
initial_pose_y	double	0.0 [m]	initial y coordinate of particles
initial_pose_a	double	0.0 [rad]	initial yaw coordinate of particles
odom_fw_dev_per_fw	double	0.19 [m/m]	standard deviation of forward motion noise by forward motion
odom_fw_dev_per_rot	double	0.0001 [m/rad]	standard deviation of forward motion noise by rotational motion
odom_rot_dev_per_fw	double	0.13 [rad/m]	standard deviation of rotational motion noise by forward motion
odom_rot_dev_per_rot	double	0.2 [rad/rad]	standard deviation of rotational motion noise by rotational motion
laser_likelihood_max_dist	double	0.2 meters	maximum distance to inflate occupied cells on the likelihood field map
scan_increment	int	1	increment number when beams are picked from their sequence
alpha_threshold	double	0.5	threshold of the alpha value for expansion resetting
open_space_threshold	double	0.05	threshold of the valid beam rate for expansion resetting
expansion_radius_position	double	0.1 [m]	maximum change of the position on the xy-plane when the reset replaces a particle
expansion_radius_orientation	double	0.2 [rad]	maximum change of the yaw angle when the reset replaces a particle
extraction_rate	double	0.1	rate of particles that are checked by the node
range_threshold	double	0.3 [rad]	threshold of the range of lasers
sensor_reset	bool	true	flag for sensor resettings

The followings have never been implemented yet.

Name	Type	Default	Description
laser_min_range	double	0.0 [m]	threshold for discarding scans whose ranges are smaller than this value
laser_max_range	double	100000000.0 [m]	threshold for discarding scans whose ranges are larger than this value

To do

• Implement service
• Fix a bug that caused particles to survive

citation

Footnotes

1. R. Ueda: "Syokai Kakuritsu Robotics (lecture note on probabilistic robotics)," Kodansya, 2019. ↩

2. R. Ueda, T. Arai, K. Sakamoto, T. Kikuchi, S. Kamiya: Expansion resetting for recovery from fatal error in Monte Carlo localization - comparison with sensor resetting methods, IEEE/RSJ IROS, pp.2481-2486, 2004. ↩