Regulated Pure Pursuit

Source code on Github.

The Regulated Pure Pursuit controller implements a variation on the Pure Pursuit controller that specifically targeting service / industrial robot needs. It regulates the linear velocities by curvature of the path to help reduce overshoot at high speeds around blind corners allowing operations to be much more safe. It also better follows paths than any other variation currently available of Pure Pursuit. It also has heuristics to slow in proximity to other obstacles so that you can slow the robot automatically when nearby potential collisions. It also implements the Adaptive lookahead point features to be scaled by velocities to enable more stable behavior in a larger range of translational speeds.

See the package's README for more complete information.

If you use the Regulated Pure Pursuit Controller algorithm or software from this repository, please cite this work in your papers:

S. Macenski, S. Singh, F. Martin, J. Gines, Regulated Pure Pursuit for Robot Path Tracking. Autonomous Robots, 2023.

Regulated Pure Pursuit Parameters

`desired_linear_vel`

Type: double Default: 0.5: The desired maximum linear velocity (m/s) to use.

`lookahead_dist`

Type: double Default: 0.6: The lookahead distance (m) to use to find the lookahead point when use_velocity_scaled_lookahead_dist is false.

`min_lookahead_dist`

Type: double Default: 0.3: The minimum lookahead distance (m) threshold when use_velocity_scaled_lookahead_dist is true.

`max_lookahead_dist`

Type: double Default: 0.9: The maximum lookahead distance (m) threshold when use_velocity_scaled_lookahead_dist is true.

`lookahead_time`

Type: double Default: 1.5: The time (s) to project the velocity by when use_velocity_scaled_lookahead_dist is true. Also known as the lookahead gain.

`rotate_to_heading_angular_vel`

Type: double Default: 1.8: If use_rotate_to_heading is true, this is the angular velocity to use.

`transform_tolerance`

Type: double Default: 0.1: The TF transform tolerance (s).

`use_velocity_scaled_lookahead_dist`

Type: bool Default: false: Whether to use the velocity scaled lookahead distances or constant lookahead_distance.

`min_approach_linear_velocity`

Type: double Default: 0.05: The minimum velocity (m/s) threshold to apply when approaching the goal to ensure progress. Must be > 0.01.

`approach_velocity_scaling_dist`

Type: double Default: 0.6: The distance (m) left on the path at which to start slowing down. Should be less than the half the costmap width.

`use_collision_detection`

Type: bool Default: true: Whether to enable collision detection.

`max_allowed_time_to_collision_up_to_carrot`

Type: double Default: 1.0: The time (s) to forward-simulate the current velocity command to check for collisions when use_collision_detection is true. At each simulation step, the robot's footprint is projected forward by the costmap resolution. The simulation stops at whichever limit is reached first: this time limit or the carrot distance. If a collision is detected at any projected pose, the robot will stop. When min_distance_to_obstacle is set, this time limit may be automatically extended to ensure the minimum obstacle distance can be checked at the current velocity. Pre-Humble, this was max_allowed_time_to_collision.

`use_regulated_linear_velocity_scaling`

Type: bool Default: true: Whether to use the regulated features for path curvature (e.g. slow on high curvature paths).

`use_cost_regulated_linear_velocity_scaling`

Type: bool Default: true: Whether to use the regulated features for proximity to obstacles (e.g. slow in close proximity to obstacles).

`cost_scaling_dist`

Type: double Default: 0.6: The minimum distance from an obstacle to trigger the scaling of linear velocity, if use_cost_regulated_linear_velocity_scaling is enabled. The value set should be smaller or equal to the inflation_radius set in the inflation layer of costmap, since inflation is used to compute the distance from obstacles.

`cost_scaling_gain`

Type: double Default: 1.0: A multiplier gain, which should be <= 1.0, used to further scale the speed when an obstacle is within cost_scaling_dist. Lower value reduces speed more quickly.

`regulated_linear_scaling_min_radius`

Type: double Default: 0.9: The turning radius (m) for which the regulation features are triggered when use_regulated_linear_velocity_scaling is true. Remember, sharper turns have smaller radii.

`regulated_linear_scaling_min_speed`

Type: double Default: 0.25: The minimum speed (m/s) for which any of the regulated heuristics can send, to ensure process is still achievable even in high cost spaces with high curvature. Must be > 0.1.

`use_fixed_curvature_lookahead`

Type: bool Default: false: Whether to use a fixed lookahead distance to compute curvature from. Since a lookahead distance may be set to vary on velocity, it can introduce a reference cycle that can be problematic for large lookahead distances.

`curvature_lookahead_dist`

Type: double Default: 0.6: Distance to look ahead on the path to detect curvature.

`use_rotate_to_heading`

Type: bool Default: true

Whether to enable rotating to rough heading and goal orientation when using holonomic planners. Recommended on for all robot types that can rotate in place.

Note: Both use_rotate_to_heading and allow_reversing cannot be set to true at the same time as it would result in ambiguous situations.

`allow_reversing`

Type: bool Default: false: Enables the robot to drive in the reverse direction, when the path planned involves reversing (which is represented by orientation cusps). Variants of the smac_planner comes with the support of reversing. Checkout the Smac Planner to know more.

`rotate_to_heading_min_angle`

Type: double Default: 0.785: The difference in the path orientation and the starting robot orientation (radians) to trigger a rotate in place, if use_rotate_to_heading is true.

`max_angular_accel`

Type: double Default: 3.2: Maximum allowable angular acceleration (rad/s/s) while rotating to heading, if use_rotate_to_heading is true.

`use_cancel_deceleration`

Type: bool Default: false: Whether to use deceleration when the goal is canceled.

`cancel_deceleration`

Type: double Default: 3.2: Linear deceleration (m/s/s) to apply when the goal is canceled.

`max_robot_pose_search_dist`

Type: double Default: Local costmap max extent (max(width, height) / 2): Upper bound on integrated distance along the global plan to search for the closest pose to the robot pose. This should be left as the default unless there are paths with loops and intersections that do not leave the local costmap, in which case making this value smaller is necessary to prevent shortcutting. If set to -1, it will use the maximum distance possible to search every point on the path for the nearest path point.

`interpolate_curvature_after_goal`

Type: bool Default: false

Interpolate a carrot after the goal dedicated to the curvate calculation (to avoid oscilaltions at the end of the path). For visualization, it will be published on the /curvature_lookahead_point topic similarly to /lookahead_point

Note: Needs use_fixed_curvature_lookahead to be true

`stateful`

Type: bool Default: true: Enables stateful goal handling behavior. When set to true, the controller will persist the goal state once the robot reaches the XY tolerance. It will then focus on aligning to the goal heading without reverting to XY position corrections.

Example

controller_server:
  ros__parameters:
    controller_frequency: 20.0
    min_x_velocity_threshold: 0.001
    min_y_velocity_threshold: 0.5
    min_theta_velocity_threshold: 0.001
    progress_checker_plugins: ["progress_checker"] # progress_checker_plugin: "progress_checker" For Humble and older
    goal_checker_plugins: ["goal_checker"]
    controller_plugins: ["FollowPath"]

    progress_checker:
      plugin: "nav2_controller::SimpleProgressChecker"
      required_movement_radius: 0.5
      movement_time_allowance: 10.0
    goal_checker:
      plugin: "nav2_controller::SimpleGoalChecker"
      xy_goal_tolerance: 0.25
      yaw_goal_tolerance: 0.25
      stateful: True
    FollowPath:
      plugin: "nav2_regulated_pure_pursuit_controller::RegulatedPurePursuitController"
      desired_linear_vel: 0.5
      lookahead_dist: 0.6
      min_lookahead_dist: 0.3
      max_lookahead_dist: 0.9
      lookahead_time: 1.5
      rotate_to_heading_angular_vel: 1.8
      transform_tolerance: 0.1
      use_velocity_scaled_lookahead_dist: false
      min_approach_linear_velocity: 0.05
      approach_velocity_scaling_dist: 0.6
      use_collision_detection: true
      max_allowed_time_to_collision_up_to_carrot: 1.0
      use_regulated_linear_velocity_scaling: true
      use_fixed_curvature_lookahead: false
      curvature_lookahead_dist: 0.25
      use_cost_regulated_linear_velocity_scaling: false
      cost_scaling_dist: 0.3
      cost_scaling_gain: 1.0
      regulated_linear_scaling_min_radius: 0.9
      regulated_linear_scaling_min_speed: 0.25
      use_rotate_to_heading: true
      allow_reversing: false
      rotate_to_heading_min_angle: 0.785
      max_angular_accel: 3.2
      max_robot_pose_search_dist: 10.0
      stateful: true