README.md

emcl2: mcl with expansion resetting (version 2)

ROS 2 version is available!!

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 an improved version of ryuichi/emcl. This version works well in crowded or outdoor environments.

demo movies

Nodes

emcl2_node

This node calculates the alpha value with a different algorithm than emcl_node in ryuichi/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

• scan (sensor_msgs/LaserScan)
  • laser scans
• tf (tf/tfMessage)
  • transforms
• initialpose (geometry_msgs/PoseWithCovarianceStamped)
  • pose of particles for replacement

Published Topics

• 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

Services

• global_localization (std_srvs/Empty)
  • Initiate global localization, wherein all particles are dispersed randomly through the free space in the map.

Services Called

• static_map (nav_msgs/GetMap)
  • Initiate the map for localization.

parameters

• ~odom_freq (int, default: 20 [Hz])
  • frequency of odometry update
• ~num_particles (int, default: 1000)
  • number of particles
• ~odom_frame_id (string, default: "odom")
  • the frame for odometry
• ~footprint_frame_id (string, default: "base_footprint")
  • the frame of the localized robot's base
• ~base_frame_id (string, default: "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, default: "map")
  • the frame for localization
• ~initial_pose_x (double, default: 0.0 [m])
  • initial x coordinate of particles
• ~initial_pose_y (double, default: 0.0 [m])
  • initial y coordinate of particles
• ~initial_pose_a (double, default: 0.0 [rad])
  • initial yaw coordinate of particles
• ~odom_fw_dev_per_fw (double, default: 0.19 [m/m])
  • standard deviation of forward motion noise by forward motion
• ~odom_fw_dev_per_rot (double, default: 0.0001 [m/rad])
  • standard deviation of forward motion noise by rotational motion
• ~odom_rot_dev_per_fw (double, default: 0.13 [rad/m])
  • standard deviation of rotational motion noise by forward motion
• ~odom_rot_dev_per_rot (double, default: 0.2 [rad/rad])
  • standard deviation of rotational motion noise by rotational motion
• ~laser_likelihood_max_dist (double, default: 0.2 meters)
  • maximum distance to inflate occupied cells on the likelihood field map
• ~scan_increment (int, default: 1)
  • increment number when beams are picked from their sequence; the larger this number is, the fewer number of beams are used for calculation of likelihood
• ~alpha_threshold (double, default: 0.5)
  • threshold of the alpha value for expansion resetting
• ~open_space_threshold (double, default: 0.05)
  • threshold of the valid beam rate for expansion resetting; the reset doesn't occur when the rate of beams in the valid range is smaller than this threshold
• ~expansion_radius_position (double, default: 0.1[m])
  • maximum change of the position on the xy-plane when the reset replaces a particle
• ~expansion_radius_orientation (double, default: 0.2[rad])
  • maximum change of the yaw angle when the reset replaces a particle
• ~extraction_rate (double, default: 0.1)
  • rate of particles that are checked by the node
• ~range_threshold (double, default: 0.1[rad])
  • threshold of the range of lasers; if all lasers on this range penetrate occupancy cells, the pose of the particle is judged as wrong
• ~sensor_reset (bool, default: true)
  • flag for sensor resettings

The followings have never been implemented yet.

• ~laser_min_range (double, default: 0.0[m])
  • threshold for discarding scans whose ranges are smaller than this value
• ~laser_max_range (double, default: 100000000.0[m])
  • threshold for discarding scans whose ranges are larger than this value

usage examples

• https://jglobal.jst.go.jp/detail?JGLOBAL_ID=202302248427441458

ROS version

• ROS Noetic Ninjemys (on Ubuntu 20.04 LTS, test on my note PC)
• ROS Melodic Morenia (on Ubuntu 18.04 LTS, test on GitHub Actions)

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. ↩