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Motion Utils package#

Definition of terms#

Segment#

Segment in Autoware is the line segment between two successive points as follows.

segment

The nearest segment index and nearest point index to a certain position is not always th same. Therefore, we prepare two different utility functions to calculate a nearest index for points and segments.

In this section, the nearest index and nearest segment index search is explained.

We have the same functions for the nearest index search and nearest segment index search. Taking for the example the nearest index search, we have two types of functions.

The first function finds the nearest index with distance and yaw thresholds.

template <class T>
size_t findFirstNearestIndexWithSoftConstraints(
  const T & points, const geometry_msgs::msg::Pose & pose,
  const double dist_threshold = std::numeric_limits<double>::max(),
  const double yaw_threshold = std::numeric_limits<double>::max());

This function finds the first local solution within thresholds. The reason to find the first local one is to deal with some edge cases explained in the next subsection.

There are default parameters for thresholds arguments so that you can decide which thresholds to pass to the function.

  1. When both the distance and yaw thresholds are given.
    • First, try to find the nearest index with both the distance and yaw thresholds.
    • If not found, try to find again with only the distance threshold.
    • If not found, find without any thresholds.
  2. When only distance are given.
    • First, try to find the nearest index the distance threshold.
    • If not found, find without any thresholds.
  3. When no thresholds are given.
    • Find the nearest index.

The second function finds the nearest index in the lane whose id is lane_id.

size_t findNearestIndexFromLaneId(
  const tier4_planning_msgs::msg::PathWithLaneId & path,
  const geometry_msgs::msg::Point & pos, const int64_t lane_id);

Application to various object#

Many node packages often calculate the nearest index of objects. We will explain the recommended method to calculate it.

Nearest index for the ego#

Assuming that the path length before the ego is short enough, we expect to find the correct nearest index in the following edge cases by findFirstNearestIndexWithSoftConstraints with both distance and yaw thresholds. Blue circles describes the distance threshold from the base link position and two blue lines describe the yaw threshold against the base link orientation. Among points in these cases, the correct nearest point which is red can be found.

ego_nearest_search

Therefore, the implementation is as follows.

const size_t ego_nearest_idx = findFirstNearestIndexWithSoftConstraints(points, ego_pose, ego_nearest_dist_threshold, ego_nearest_yaw_threshold);
const size_t ego_nearest_seg_idx = findFirstNearestIndexWithSoftConstraints(points, ego_pose, ego_nearest_dist_threshold, ego_nearest_yaw_threshold);

Nearest index for dynamic objects#

For the ego nearest index, the orientation is considered in addition to the position since the ego is supposed to follow the points. However, for the dynamic objects (e.g., predicted object), sometimes its orientation may be different from the points order, e.g. the dynamic object driving backward although the ego is driving forward.

Therefore, the yaw threshold should not be considered for the dynamic object. The implementation is as follows.

const size_t dynamic_obj_nearest_idx = findFirstNearestIndexWithSoftConstraints(points, dynamic_obj_pose, dynamic_obj_nearest_dist_threshold);
const size_t dynamic_obj_nearest_seg_idx = findFirstNearestIndexWithSoftConstraints(points, dynamic_obj_pose, dynamic_obj_nearest_dist_threshold);

Nearest index for traffic objects#

In lanelet maps, traffic objects belong to the specific lane. With this specific lane's id, the correct nearest index can be found.

The implementation is as follows.

// first extract `lane_id` which the traffic object belong to.
const size_t traffic_obj_nearest_idx = findNearestIndexFromLaneId(path_with_lane_id, traffic_obj_pos, lane_id);
const size_t traffic_obj_nearest_seg_idx = findNearestSegmentIndexFromLaneId(path_with_lane_id, traffic_obj_pos, lane_id);

For developers#

Some of the template functions in trajectory.hpp are mostly used for specific types (autoware_planning_msgs::msg::PathPoint, autoware_planning_msgs::msg::PathPoint, autoware_planning_msgs::msg::TrajectoryPoint), so they are exported as extern template functions to speed-up compilation time.

autoware_motion_utils.hpp header file was removed because the source files that directly/indirectly include this file took a long time for preprocessing.