Obstacle Stop

Role

The obstacle_stop module does the stop planning when there is a static obstacle near the trajectory.

Activation

This module is activated if the launch parameter launch_obstacle_stop_module is set to true.

Inner-workings / Algorithms

Obstacle Filtering

The obstacles meeting the following condition are determined as obstacles for stopping.

• The object type is for stopping according to obstacle_filtering.object_type.*.
• The lateral distance from the object to the ego's trajectory is smaller than obstacle_filtering.max_lat_margin.
• The object velocity along the ego's trajectory is smaller than obstacle_filtering.obstacle_velocity_threshold_from_stop.
• The object
  • does not cross the ego's trajectory (*1)
  • and its collision time margin is large enough (*2).

NOTE

*1: Crossing obstacles

Crossing obstacle is the object whose orientation's yaw angle against the ego's trajectory is smaller than obstacle_filtering.crossing_obstacle.obstacle_traj_angle_threshold.

*2: Enough collision time margin

We predict the collision area and its time by the ego with a constant velocity motion and the obstacle with its predicted path. Then, we calculate a collision time margin which is the difference of the time when the ego will be inside the collision area and the obstacle will be inside the collision area. When this time margin is smaller than obstacle_filtering.crossing_obstacle.collision_time_margin, the margin is not enough.

Stop Planning

The role of the stop planning is keeping a safe distance with static vehicle objects or dynamic/static non vehicle objects.

The stop planning just inserts the stop point in the trajectory to keep a distance with obstacles. The safe distance is parameterized as stop_planning.stop_margin. When it stops at the end of the trajectory, and obstacle is on the same point, the safe distance becomes stop_planning.terminal_stop_margin.

When inserting the stop point, the required acceleration for the ego to stop in front of the stop point is calculated. If the acceleration is less than common.min_strong_accel, the stop planning will be cancelled since this package does not assume a strong sudden brake for emergency.

Minor functions

Prioritization of behavior module's stop point

When stopping for a pedestrian walking on the crosswalk, the behavior module inserts the zero velocity in the trajectory in front of the crosswalk. Also autoware_obstacle_cruise_planner's stop planning also works, and the ego may not reach the behavior module's stop point since the safe distance defined in autoware_obstacle_cruise_planner may be longer than the behavior module's safe distance. To resolve this non-alignment of the stop point between the behavior module and this module, stop_planning.min_behavior_stop_margin is defined. In the case of the crosswalk described above, this module inserts the stop point with a distance stop_planning.min_behavior_stop_margin at minimum between the ego and obstacle.

A function to keep the closest stop obstacle in target obstacles

In order to keep the closest stop obstacle in the target obstacles, we check whether it is disappeared or not from the target obstacles in the check_consistency function. If the previous closest stop obstacle is remove from the lists, we keep it in the lists for obstacle_filtering.stop_obstacle_hold_time_threshold seconds. Note that if a new stop obstacle appears and the previous closest obstacle removes from the lists, we do not add it to the target obstacles again.

Debugging

Detection area

Green polygons which is a detection area is visualized by detection_polygons in the ~/debug/marker topic.

Collision points

Red points which are collision points with obstacle are visualized by *_collision_points for each behavior in the ~/debug/marker topic.

Obstacle for stop

Red sphere which is an obstacle for stop is visualized by obstacles_to_stop in the ~/debug/marker topic.

Red wall which means a safe distance to stop if the ego's front meets the wall is visualized in the ~/virtual_wall topic.