Goal Planner design

Purpose / Role

Plan path around the goal.

• Park at the designated goal.
• Modify the goal to avoid obstacles or to pull over at the side of tha lane.

Design

If goal modification is not allowed, park at the designated fixed goal. (fixed_goal_planner in the figure below) When allowed, park in accordance with the specified policy(e.g pull over on left/right side of the lane). (rough_goal_planner in the figure below). Currently rough goal planner only support pull_over feature, but it would be desirable to be able to accommodate various parking policies in the future.

start condition

Either one is activated when all conditions are met.

fixed_goal_planner

• Route is set with allow_goal_modification=false by default.
• ego-vehicle is in the same lane as the goal.

If the target path contains a goal, modify the points of the path so that the path and the goal are connected smoothly. This process will change the shape of the path by the distance of refine_goal_search_radius_range from the goal. Note that this logic depends on the interpolation algorithm that will be executed in a later module (at the moment it uses spline interpolation), so it needs to be updated in the future.

rough_goal_planner

pull over on road lane

• The distance between the goal and ego-vehicle is shorter than pull_over_minimum_request_length.
• Route is set with allow_goal_modification=true .
  • We can set this option with SetRoute api service.
  • We support 2D Rough Goal Pose with the key bind r in RViz, but in the future there will be a panel of tools to manipulate various Route API from RViz.
• ego-vehicle is in the same lane as the goal.

pull over on shoulder lane

• The distance between the goal and ego-vehicle is shorter than pull_over_minimum_request_length.
• Goal is set in the road_shoulder.

finish condition

• The distance to the goal from your vehicle is lower than threshold (default: < 1m).
• The ego-vehicle is stopped.
  • The speed is lower than threshold (default: < 0.01m/s).

General parameters for goal_planner

Name	Unit	Type	Description	Default value
th_arrived_distance	[m]	double	distance threshold for arrival of path termination	1.0
th_stopped_velocity	[m/s]	double	velocity threshold for arrival of path termination	0.01
th_stopped_time	[s]	double	time threshold for arrival of path termination	2.0
center_line_path_interval	[m]	double	reference center line path point interval	1.0

collision check

occupancy grid based collision check

Generate footprints from ego-vehicle path points and determine obstacle collision from the value of occupancy_grid of the corresponding cell.

Parameters for occupancy grid based collision check

Name	Unit	Type	Description	Default value
use_occupancy_grid_for_goal_search	[-]	bool	flag whether to use occupancy grid for goal search collision check	true
use_occupancy_grid_for_goal_longitudinal_margin	[-]	bool	flag whether to use occupancy grid for keeping longitudinal margin	false
use_occupancy_grid_for_path_collision_check	[-]	bool	flag whether to use occupancy grid for collision check	false
occupancy_grid_collision_check_margin	[m]	double	margin to calculate ego-vehicle cells from footprint.	0.0
theta_size	[-]	int	size of theta angle to be considered. angular resolution for collision check will be 2\(\pi\) / theta_size [rad].	360
obstacle_threshold	[-]	int	threshold of cell values to be considered as obstacles	60

object recognition based collision check

Parameters for object recognition based collision check

Name	Unit	Type	Description	Default value
use_object_recognition	[-]	bool	flag whether to use object recognition for collision check	true
object_recognition_collision_check_margin	[m]	double	margin to calculate ego-vehicle cells from footprint.	0.6
object_recognition_collision_check_max_extra_stopping_margin	[m]	double	maximum value when adding longitudinal distance margin for collision check considering stopping distance	1.0
detection_bound_offset	[m]	double	expand pull over lane with this offset to make detection area for collision check of path generation	15.0

Goal Search

If it is not possible to park safely at a given goal, /planning/scenario_planning/modified_goal is searched for in certain range of the shoulder lane.

goal search video

Parameters for goal search

Name	Unit	Type	Description	Default value
goal_priority	[-]	string	In case minimum_weighted_distance, sort with smaller longitudinal distances taking precedence over smaller lateral distances. In case minimum_longitudinal_distance, sort with weighted lateral distance against longitudinal distance.	minimum_weighted_distance
prioritize_goals_before_objects	[-]	bool	If there are objects that may need to be avoided, prioritize the goal in front of them	true
forward_goal_search_length	[m]	double	length of forward range to be explored from the original goal	20.0
backward_goal_search_length	[m]	double	length of backward range to be explored from the original goal	20.0
goal_search_interval	[m]	double	distance interval for goal search	2.0
longitudinal_margin	[m]	double	margin between ego-vehicle at the goal position and obstacles	3.0
max_lateral_offset	[m]	double	maximum offset of goal search in the lateral direction	0.5
lateral_offset_interval	[m]	double	distance interval of goal search in the lateral direction	0.25
ignore_distance_from_lane_start	[m]	double	distance from start of pull over lanes for ignoring goal candidates	0.0
ignore_distance_from_lane_start	[m]	double	distance from start of pull over lanes for ignoring goal candidates	0.0
margin_from_boundary	[m]	double	distance margin from edge of the shoulder lane	0.5

Pull Over

There are three path generation methods. The path is generated with a certain margin (default: 0.5 m) from the boundary of shoulder lane.

Name	Unit	Type	Description	Default value
pull_over_minimum_request_length	[m]	double	when the ego-vehicle approaches the goal by this distance or a safe distance to stop, pull over is activated.	100.0
pull_over_velocity	[m/s]	double	decelerate to this speed by the goal search area	3.0
pull_over_minimum_velocity	[m/s]	double	speed of pull_over after stopping once. this prevents excessive acceleration.	1.38
decide_path_distance	[m]	double	decide path if it approaches this distance relative to the parking position. after that, no path planning and goal search are performed	10.0
maximum_deceleration	[m/s2]	double	maximum deceleration. it prevents sudden deceleration when a parking path cannot be found suddenly	1.0
path_priority	[-]	string	In case efficient_path use a goal that can generate an efficient path which is set in efficient_path_order. In case close_goal use the closest goal to the original one.	efficient_path
efficient_path_order	[-]	string	efficient order of pull over planner along lanes　excluding freespace pull over	["SHIFT", "ARC_FORWARD", "ARC_BACKWARD"]

shift parking

Pull over distance is calculated by the speed, lateral deviation, and the lateral jerk. The lateral jerk is searched for among the predetermined minimum and maximum values, and the one satisfies ready conditions described above is output.

1. Apply uniform offset to centerline of shoulder lane for ensuring margin
2. In the section between merge start and end, path is shifted by a method that is used to generate avoidance path (four segmental constant jerk polynomials)
3. Combine this path with center line of road lane

shift_parking video

Parameters for shift parking

Name	Unit	Type	Description	Default value
enable_shift_parking	[-]	bool	flag whether to enable shift parking	true
shift_sampling_num	[-]	int	Number of samplings in the minimum to maximum range of lateral_jerk	4
maximum_lateral_jerk	[m/s3]	double	maximum lateral jerk	2.0
minimum_lateral_jerk	[m/s3]	double	minimum lateral jerk	0.5
deceleration_interval	[m]	double	distance of deceleration section	15.0
after_shift_straight_distance	[m]	double	straight line distance after pull over end point	1.0

geometric parallel parking

Generate two arc paths with discontinuous curvature. It stops twice in the middle of the path to control the steer on the spot. There are two path generation methods: forward and backward. See also [1] for details of the algorithm. There is also a simple python implementation.

Parameters geometric parallel parking

Name	Unit	Type	Description	Default value
arc_path_interval	[m]	double	interval between arc path points	1.0
pull_over_max_steer_rad	[rad]	double	maximum steer angle for path generation. it may not be possible to control steer up to max_steer_angle in vehicle_info when stopped	0.35

arc forward parking

Generate two forward arc paths.

arc_forward_parking video

Parameters arc forward parking

Name	Unit	Type	Description	Default value
enable_arc_forward_parking	[-]	bool	flag whether to enable arc forward parking	true
after_forward_parking_straight_distance	[m]	double	straight line distance after pull over end point	2.0
forward_parking_velocity	[m/s]	double	velocity when forward parking	1.38
forward_parking_lane_departure_margin	[m/s]	double	lane departure margin for front left corner of ego-vehicle when forward parking	0.0

arc backward parking

Generate two backward arc paths.

.

arc_backward_parking video

Parameters arc backward parking

Name	Unit	Type	Description	Default value
enable_arc_backward_parking	[-]	bool	flag whether to enable arc backward parking	true
after_backward_parking_straight_distance	[m]	double	straight line distance after pull over end point	2.0
backward_parking_velocity	[m/s]	double	velocity when backward parking	-1.38
backward_parking_lane_departure_margin	[m/s]	double	lane departure margin for front right corner of ego-vehicle when backward	0.0

freespace parking

If the vehicle gets stuck with lane_parking, run freespace_parking. To run this feature, you need to set parking_lot to the map, activate_by_scenario of costmap_generator to false and enable_freespace_parking to true

Simultaneous execution with avoidance_module in the flowchart is under development.

Unimplemented parts / limitations for freespace parking

• When a short path is generated, the ego does can not drive with it.
• Complex cases take longer to generate or fail.
• The drivable area is not guaranteed to fit in the parking_lot.

Parameters freespace parking

Name	Unit	Type	Description	Default value
enable_freespace_parking	[-]	bool	This flag enables freespace parking, which runs when the vehicle is stuck due to e.g. obstacles in the parking area.	true

See freespace_planner for other parameters.