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Obstacle Cruise Planner#

Overview#

The autoware_obstacle_cruise_planner package has following modules.

  • Stop planning
    • stop when there is a static obstacle near the trajectory.
  • Cruise planning
    • cruise a dynamic obstacle in front of the ego.
  • Slow down planning
    • slow down when there is a static/dynamic obstacle near the trajectory.

Interfaces#

Input topics#

Name Type Description
~/input/trajectory autoware_planning_msgs::Trajectory input trajectory
~/input/objects autoware_perception_msgs::PredictedObjects dynamic objects
~/input/odometry nav_msgs::msg::Odometry ego odometry

Output topics#

Name Type Description
~/output/trajectory autoware_planning_msgs::Trajectory output trajectory
~/output/velocity_limit tier4_planning_msgs::VelocityLimit velocity limit for cruising
~/output/clear_velocity_limit tier4_planning_msgs::VelocityLimitClearCommand clear command for velocity limit
~/output/stop_reasons tier4_planning_msgs::StopReasonArray reasons that make the vehicle to stop

Design#

Design for the following functions is defined here.

  • Behavior determination against obstacles
  • Stop planning
  • Cruise planning
  • Slow down planning

A data structure for cruise and stop planning is as follows. This planner data is created first, and then sent to the planning algorithm.

struct PlannerData
{
  rclcpp::Time current_time;
  autoware_planning_msgs::msg::Trajectory traj;
  geometry_msgs::msg::Pose current_pose;
  double ego_vel;
  double current_acc;
  std::vector<Obstacle> target_obstacles;
};

struct Obstacle
{
  rclcpp::Time stamp;  // This is not the current stamp, but when the object was observed.
  geometry_msgs::msg::Pose pose;  // interpolated with the current stamp
  bool orientation_reliable;
  Twist twist;
  bool twist_reliable;
  ObjectClassification classification;
  std::string uuid;
  Shape shape;
  std::vector<PredictedPath> predicted_paths;
};

Behavior determination against obstacles#

Obstacles for cruising, stopping and slowing down are selected in this order based on their pose and velocity. The obstacles not in front of the ego will be ignored.

determine_cruise_stop_slow_down

Determine cruise vehicles#

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

  • The lateral distance from the object to the ego's trajectory is smaller than behavior_determination.cruise.max_lat_margin.
  • The object type is for cruising according to common.cruise_obstacle_type.*.
  • The object is not crossing the ego's trajectory (*1).
  • If the object is inside the trajectory.
    • The object type is for inside cruising according to common.cruise_obstacle_type.inside.*.
    • The object velocity is larger than behavior_determination.obstacle_velocity_threshold_from_cruise_to_stop.
  • If the object is outside the trajectory.
    • The object type is for outside cruising according to common.cruise_obstacle_type.outside.*.
    • The object velocity is larger than behavior_determination.cruise.outside_obstacle.obstacle_velocity_threshold.
    • The highest confident predicted path collides with the ego's trajectory.
    • Its collision's period is larger than behavior_determination.cruise.outside_obstacle.ego_obstacle_overlap_time_threshold.
Parameter Type Description
common.cruise_obstacle_type.inside.unknown bool flag to consider unknown objects for cruising
common.cruise_obstacle_type.inside.car bool flag to consider unknown objects for cruising
common.cruise_obstacle_type.inside.truck bool flag to consider unknown objects for cruising
... bool ...
common.cruise_obstacle_type.outside.unknown bool flag to consider unknown objects for cruising
common.cruise_obstacle_type.outside.car bool flag to consider unknown objects for cruising
common.cruise_obstacle_type.outside.truck bool flag to consider unknown objects for cruising
... bool ...
behavior_determination.cruise.max_lat_margin double maximum lateral margin for cruise obstacles
behavior_determination.obstacle_velocity_threshold_from_cruise_to_stop double maximum obstacle velocity for cruise obstacle inside the trajectory
behavior_determination.cruise.outside_obstacle.obstacle_velocity_threshold double maximum obstacle velocity for cruise obstacle outside the trajectory
behavior_determination.cruise.outside_obstacle.ego_obstacle_overlap_time_threshold double maximum overlap time of the collision between the ego and obstacle
Yield for vehicles that might cut in into the ego's lane#

It is also possible to yield (cruise) behind vehicles in neighbor lanes if said vehicles might cut in the ego vehicle's current lane.

The obstacles meeting the following condition are determined as obstacles for yielding (cruising).

  • The object type is for cruising according to common.cruise_obstacle_type.* and it is moving with a speed greater than behavior_determination.cruise.yield.stopped_obstacle_velocity_threshold.
  • The object is not crossing the ego's trajectory (*1).
  • There is another object of type common.cruise_obstacle_type.* stopped in front of the moving obstacle.
  • The lateral distance (using the ego's trajectory as reference) between both obstacles is less than behavior_determination.cruise.yield.max_lat_dist_between_obstacles
  • Both obstacles, moving and stopped, are within behavior_determination.cruise.yield.lat_distance_threshold and behavior_determination.cruise.yield.lat_distance_threshold + behavior_determination.cruise.yield.max_lat_dist_between_obstacles lateral distance from the ego's trajectory respectively.

If the above conditions are met, the ego vehicle will cruise behind the moving obstacle, yielding to it so it can cut in into the ego's lane to avoid the stopped obstacle.

Determine stop vehicles#

Among obstacles which are not for cruising, the obstacles meeting the following condition are determined as obstacles for stopping.

  • The object type is for stopping according to common.stop_obstacle_type.*.
  • The lateral distance from the object to the ego's trajectory is smaller than behavior_determination.stop.max_lat_margin.
  • The object velocity along the ego's trajectory is smaller than behavior_determination.obstacle_velocity_threshold_from_stop_to_cruise.
  • The object
    • does not cross the ego's trajectory (*1)
    • with the velocity smaller than behavior_determination.crossing_obstacle.obstacle_velocity_threshold
    • and its collision time margin is large enough (*2).
Parameter Type Description
common.stop_obstacle_type.unknown bool flag to consider unknown objects for stopping
common.stop_obstacle_type.car bool flag to consider unknown objects for stopping
common.stop_obstacle_type.truck bool flag to consider unknown objects for stopping
... bool ...
behavior_determination.stop.max_lat_margin double maximum lateral margin for stop obstacles
behavior_determination.crossing_obstacle.obstacle_velocity_threshold double maximum crossing obstacle velocity to ignore
behavior_determination.obstacle_velocity_threshold_from_stop_to_cruise double maximum obstacle velocity for stop

Determine slow down vehicles#

Among obstacles which are not for cruising and stopping, the obstacles meeting the following condition are determined as obstacles for slowing down.

  • The object type is for slowing down according to common.slow_down_obstacle_type.*.
  • The lateral distance from the object to the ego's trajectory is smaller than behavior_determination.slow_down.max_lat_margin.
Parameter Type Description
common.slow_down_obstacle_type.unknown bool flag to consider unknown objects for slowing down
common.slow_down_obstacle_type.car bool flag to consider unknown objects for slowing down
common.slow_down_obstacle_type.truck bool flag to consider unknown objects for slowing down
... bool ...
behavior_determination.slow_down.max_lat_margin double maximum lateral margin for slow down obstacles

NOTE#

*1: Crossing obstacles#

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

Parameter Type Description
behavior_determination.crossing_obstacle.obstacle_traj_angle_threshold double maximum angle against the ego's trajectory to judge the obstacle is crossing the trajectory [rad]
*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 behavior_determination.stop.crossing_obstacle.collision_time_margin, the margin is not enough.

Parameter Type Description
behavior_determination.stop.crossing_obstacle.collision_time_margin double maximum collision time margin of the ego and obstacle

Stop planning#

Parameter Type Description
common.min_strong_accel double ego's minimum acceleration to stop [m/ss]
common.safe_distance_margin double distance with obstacles for stop [m]
common.terminal_safe_distance_margin double terminal_distance with obstacles for stop, which cannot be exceed safe distance margin [m]

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 common.safe_distance_margin. When it stops at the end of the trajectory, and obstacle is on the same point, the safe distance becomes terminal_safe_distance_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.

Cruise planning#

Parameter Type Description
common.safe_distance_margin double minimum distance with obstacles for cruise [m]

The role of the cruise planning is keeping a safe distance with dynamic vehicle objects with smoothed velocity transition. This includes not only cruising a front vehicle, but also reacting a cut-in and cut-out vehicle.

The safe distance is calculated dynamically based on the Responsibility-Sensitive Safety (RSS) by the following equation.

\[ d_{rss} = v_{ego} t_{idling} + \frac{1}{2} a_{ego} t_{idling}^2 + \frac{v_{ego}^2}{2 a_{ego}} - \frac{v_{obstacle}^2}{2 a_{obstacle}}, \]

assuming that \(d_{rss}\) is the calculated safe distance, \(t_{idling}\) is the idling time for the ego to detect the front vehicle's deceleration, \(v_{ego}\) is the ego's current velocity, \(v_{obstacle}\) is the front obstacle's current velocity, \(a_{ego}\) is the ego's acceleration, and \(a_{obstacle}\) is the obstacle's acceleration. These values are parameterized as follows. Other common values such as ego's minimum acceleration is defined in common.param.yaml.

Parameter Type Description
common.idling_time double idling time for the ego to detect the front vehicle starting deceleration [s]
common.min_ego_accel_for_rss double ego's acceleration for RSS [m/ss]
common.min_object_accel_for_rss double front obstacle's acceleration for RSS [m/ss]

The detailed formulation is as follows.

\[ \begin{align} d_{error} & = d - d_{rss} \\ d_{normalized} & = lpf(d_{error} / d_{obstacle}) \\ d_{quad, normalized} & = sign(d_{normalized}) *d_{normalized}*d_{normalized} \\ v_{pid} & = pid(d_{quad, normalized}) \\ v_{add} & = v_{pid} > 0 ? v_{pid}* w_{acc} : v_{pid} \\ v_{target} & = max(v_{ego} + v_{add}, v_{min, cruise}) \end{align} \]
Variable Description
d actual distance to obstacle
d_{rss} ideal distance to obstacle based on RSS
v_{min, cruise} min_cruise_target_vel
w_{acc} output_ratio_during_accel
lpf(val) apply low-pass filter to val
pid(val) apply pid to val

Slow down planning#

Parameter Type Description
slow_down.labels vector(string) A vector of labels for customizing obstacle-label-based slow down behavior. Each label represents an obstacle type that will be treated differently when applying slow down. The possible labels are ("default" (Mandatory), "unknown","car","truck","bus","trailer","motorcycle","bicycle" or "pedestrian")
slow_down.default.static.min_lat_velocity double minimum velocity to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be static, or not moving
slow_down.default.static.max_lat_velocity double maximum velocity to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be static, or not moving
slow_down.default.static.min_lat_margin double minimum lateral margin to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be static, or not moving
slow_down.default.static.max_lat_margin double maximum lateral margin to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be static, or not moving
slow_down.default.moving.min_lat_velocity double minimum velocity to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be moving
slow_down.default.moving.max_lat_velocity double maximum velocity to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be moving
slow_down.default.moving.min_lat_margin double minimum lateral margin to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be moving
slow_down.default.moving.max_lat_margin double maximum lateral margin to linearly calculate slow down velocity [m]. Note: This default value will be used when the detected obstacle label does not match any of the slow_down.labels and the obstacle is considered to be moving
(optional) slow_down."label".(static & moving).min_lat_velocity double minimum velocity to linearly calculate slow down velocity [m]. Note: only for obstacles specified in slow_down.labels. Requires a static and a moving value
(optional) slow_down."label".(static & moving).max_lat_velocity double maximum velocity to linearly calculate slow down velocity [m]. Note: only for obstacles specified in slow_down.labels. Requires a static and a moving value
(optional) slow_down."label".(static & moving).min_lat_margin double minimum lateral margin to linearly calculate slow down velocity [m]. Note: only for obstacles specified in slow_down.labels. Requires a static and a moving value
(optional) slow_down."label".(static & moving).max_lat_margin double maximum lateral margin to linearly calculate slow down velocity [m]. Note: only for obstacles specified in slow_down.labels. Requires a static and a moving value

The role of the slow down planning is inserting slow down velocity in the trajectory where the trajectory points are close to the obstacles. The parameters can be customized depending on the obstacle type (see slow_down.labels), making it possible to adjust the slow down behavior depending if the obstacle is a pedestrian, bicycle, car, etc. Each obstacle type has a static and a moving parameter set, so it is possible to customize the slow down response of the ego vehicle according to the obstacle type and if it is moving or not. If an obstacle is determined to be moving, the corresponding moving set of parameters will be used to compute the vehicle slow down, otherwise, the static parameters will be used. The static and moving separation is useful for customizing the ego vehicle slow down behavior to, for example, slow down more significantly when passing stopped vehicles that might cause occlusion or that might suddenly open its doors.

An obstacle is classified as static if its total speed is less than the moving_object_speed_threshold parameter. Furthermore, a hysteresis based approach is used to avoid chattering, it uses the moving_object_hysteresis_range parameter range and the obstacle's previous state (moving or static) to determine if the obstacle is moving or not. In other words, if an obstacle was previously classified as static, it will not change its classification to moving unless its total speed is greater than moving_object_speed_threshold + moving_object_hysteresis_range. Likewise, an obstacle previously classified as moving, will only change to static if its speed is lower than moving_object_speed_threshold - moving_object_hysteresis_range.

The closest point on the obstacle to the ego's trajectory is calculated. Then, the slow down velocity is calculated by linear interpolation with the distance between the point and trajectory as follows.

slow_down_velocity_calculation

Variable Description
v_{out} calculated velocity for slow down
v_{min} slow_down.min_lat_velocity
v_{max} slow_down.max_lat_velocity
l_{min} slow_down.min_lat_margin
l_{max} slow_down.max_lat_margin
l'_{max} behavior_determination.slow_down.max_lat_margin

The calculated velocity is inserted in the trajectory where the obstacle is inside the area with behavior_determination.slow_down.max_lat_margin.

slow_down_planning

Implementation#

Flowchart#

Successive functions consist of autoware_obstacle_cruise_planner as follows.

Various algorithms for stop and cruise planning will be implemented, and one of them is designated depending on the use cases. The core algorithm implementation generateTrajectory depends on the designated algorithm.

uml diagram

Algorithm selection for cruise planner#

Currently, only a PID-based planner is supported. Each planner will be explained in the following.

Parameter Type Description
common.planning_method string cruise and stop planning algorithm, selected from "pid_base"

PID-based planner#

Stop planning#

In the pid_based_planner namespace,

Parameter Type Description
obstacle_velocity_threshold_from_cruise_to_stop double obstacle velocity threshold to be stopped from cruised [m/s]

Only one obstacle is targeted for the stop planning. It is the obstacle among obstacle candidates whose velocity is less than obstacle_velocity_threshold_from_cruise_to_stop, and which is the nearest to the ego along the trajectory. A stop point is inserted keepingcommon.safe_distance_margin distance between the ego and obstacle.

Note that, as explained in the stop planning design, a stop planning which requires a strong acceleration (less than common.min_strong_accel) will be canceled.

Cruise planning#

In the pid_based_planner namespace,

Parameter Type Description
kp double p gain for pid control [-]
ki double i gain for pid control [-]
kd double d gain for pid control [-]
output_ratio_during_accel double The output velocity will be multiplied by the ratio during acceleration to follow the front vehicle. [-]
vel_to_acc_weight double target acceleration is target velocity * vel_to_acc_weight [-]
min_cruise_target_vel double minimum target velocity during cruise [m/s]

In order to keep the safe distance, the target velocity and acceleration is calculated and sent as an external velocity limit to the velocity smoothing package (motion_velocity_smoother by default). The target velocity and acceleration is respectively calculated with the PID controller according to the error between the reference safe distance and the actual distance.

Optimization-based planner#

under construction

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 autoware_obstacle_cruise_planner, common.min_behavior_stop_margin is defined. In the case of the crosswalk described above, autoware_obstacle_cruise_planner inserts the stop point with a distance common.min_behavior_stop_margin at minimum between the ego and obstacle.

Parameter Type Description
common.min_behavior_stop_margin double minimum stop margin when stopping with the behavior module enabled [m]

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 checkConsistency function. If the previous closest stop obstacle is remove from the lists, we keep it in the lists for 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.

Parameter Type Description
behavior_determination.stop_obstacle_hold_time_threshold double maximum time for holding closest stop obstacle [s]

How To Debug#

How to debug can be seen here.

Known Limits#

  • Common
    • When the obstacle pose or velocity estimation has a delay, the ego sometimes will go close to the front vehicle keeping deceleration.
    • Current implementation only uses predicted objects message for static/dynamic obstacles and does not use pointcloud. Therefore, if object recognition is lost, the ego cannot deal with the lost obstacle.
    • The current predicted paths for obstacle's lane change does not have enough precision for obstacle_cruise_planner. Therefore, we set rough_detection_area a small value.
  • PID-based planner
    • The algorithm strongly depends on the velocity smoothing package (motion_velocity_smoother by default) whether or not the ego realizes the designated target speed. If the velocity smoothing package is updated, please take care of the vehicle's behavior as much as possible.