Dynamic avoidance design

Purpose / Role

This is a module designed for avoiding obstacles which are running. Static obstacles such as parked vehicles are dealt with by the avoidance module.

This module is under development. In the current implementation, the dynamic obstacles to avoid is extracted from the drivable area. Then the motion planner, in detail obstacle_avoidance_planner, will generate an avoiding trajectory.

Overview of drivable area modification

Filtering obstacles to avoid

The dynamics obstacles meeting the following condition will be avoided.

• The type is designated as target_object.*.
• The norm of the obstacle's velocity projected to the ego's path is smaller than target_object.min_obstacle_vel.
• The obstacle is in the next lane to the ego's lane, which will not cut-into the ego's lane according to the highest-prioritized predicted path.

Drivable area modification

To realize dynamic obstacles for avoidance, the time dimension should be take into an account considering the dynamics. However, it will make the planning problem much harder to solve. Therefore, we project the time dimension to the 2D pose dimension.

Currently, the predicted paths of predicted objects are not so stable. Therefore, instead of using the predicted paths, we assume that the obstacle will run parallel to the ego's path.

First, a maximum lateral offset to avoid is calculated as follows. The polygon's width to extract from the drivable area is the obstacle width and double drivable_area_generation.lat_offset_from_obstacle. We can limit the lateral shift offset by drivable_area_generation.max_lat_offset_to_avoid.

Then, extracting the same directional and opposite directional obstacles from the drivable area will work as follows considering TTC (time to collision). Regarding the same directional obstacles, obstacles whose TTC is negative will be ignored (e.g. The obstacle is in front of the ego, and the obstacle's velocity is larger than the ego's velocity.).

Same directional obstacles

Opposite directional obstacles

Parameters

Name	Unit	Type	Description	Default value
target_object.car	[-]	bool	The flag whether to avoid cars or not	true
target_object.truck	[-]	bool	The flag whether to avoid trucks or not	true
...	[-]	bool	...	...
target_object.min_obstacle_vel	[m/s]	double	Minimum obstacle velocity to avoid	1.0
drivable_area_generation.lat_offset_from_obstacle	[m]	double	Lateral offset to avoid from obstacles	0.8
drivable_area_generation.max_lat_offset_to_avoid	[m]	double	Maximum lateral offset to avoid	0.5
drivable_area_generation.overtaking_object.max_time_to_collision	[s]	double	Maximum value when calculating time to collision	3.0
drivable_area_generation.overtaking_object.start_duration_to_avoid	[s]	double	Duration to consider avoidance before passing by obstacles	4.0
drivable_area_generation.overtaking_object.end_duration_to_avoid	[s]	double	Duration to consider avoidance after passing by obstacles	5.0
drivable_area_generation.overtaking_object.duration_to_hold_avoidance	[s]	double	Duration to hold avoidance after passing by obstacles	3.0
drivable_area_generation.oncoming_object.max_time_to_collision	[s]	double	Maximum value when calculating time to collision	3.0
drivable_area_generation.oncoming_object.start_duration_to_avoid	[s]	double	Duration to consider avoidance before passing by obstacles	9.0
drivable_area_generation.oncoming_object.end_duration_to_avoid	[s]	double	Duration to consider avoidance after passing by obstacles	0.0