Trajectory Library

Contact: John Keller

trajectory_library is a C++ library (no node of its own) for generating and manipulating candidate trajectories for obstacle-avoidance planners. It provides the Trajectory/Waypoint classes used throughout the local layer to interpolate, transform, trim, merge, and visualize waypoint paths, plus a TrajectoryLibrary class that loads a library of candidate trajectory generators from a YAML config file — the file the DROAN local planner (asm_droan module) points its trajectory_library_config parameter at. Every trajectory converts to/from airstack_msgs/msg/TrajectoryXYZVYaw, the trajectory-controller command type (see the Interface Conventions Specification §5).

Core classes

Defined in include/trajectory_library/trajectory_library.hpp, implemented in src/trajectory_library.cpp:

Waypoint times are generated lazily from positions and speeds (generate_waypoint_times()): the time to each waypoint is segment distance divided by the average of the two endpoint speeds (floored at 0.01 m/s). When a TrajectoryXYZVYaw is ingested, each waypoint’s scalar velocity is turned into a velocity vector along the local segment direction.

Trajectory generator classes

The library distinguishes static generators (fixed shape, computed once, get_trajectory()) from dynamic generators (recomputed from the robot’s current odometry, get_trajectory(odom)):

Only curve and acceleration can be created from the YAML config; TakeoffTrajectory is constructed programmatically (the takeoff_landing_planner builds its takeoff/landing trajectories with it). Entries with any other type are silently skipped by the parser (src/trajectory_library.cpp:1284-1344).

Config file format (trajectory_library_config)

TrajectoryLibrary(config_filename, node_ptr) loads a YAML file with a single top-level key, trajectories:, a list of generator definitions. Each entry’s keys depend on its type:

type: curve → one static CurveTrajectory:

type: acceleration → one dynamic AccelerationTrajectory. The acceleration vector is given either componentwise (x/y/z) or polar (magnitude/magnitude_yaw/magnitude_pitch); if neither complete set is present the entry is rejected with a console message:

$(param <name>) substitution: any scalar value may be the string $(param name), which is replaced at load time with the value of the ROS parameter name on the node that constructed the TrajectoryLibrary (parser: include/trajectory_library/trajectory_library.hpp, parse<T>()). This is how one config file serves different speed profiles: DROAN’s droan.yaml sets dt, ht, ht_long, max_velocity, and magnitude as node parameters and the trajectory YAML references them. TrajectoryLibrary’s constructor declares these five parameter names (with placeholder defaults) so the substitution always resolves.

Real excerpt from config/long.yaml — the default library for droan_local_planner (an acceleration fan: one entry per magnitude_yaw heading, 22.5° apart, plus climbing/descending variants):

---
trajectories:
  - dt: $(param dt)
    frame: look_ahead_point_stabilized
    ht: $(param ht_long)
    magnitude: $(param magnitude)
    magnitude_pitch: 0
    magnitude_yaw: 0
    max_velocity: $(param max_velocity)
    type: acceleration
  - dt: $(param dt)
    frame: look_ahead_point_stabilized
    ht: $(param ht_long)
    magnitude: $(param magnitude)
    magnitude_pitch: 0
    magnitude_yaw: 22.5
    max_velocity: $(param max_velocity)
    type: acceleration
  # ... more headings ...

And a curve example from config/backup.yaml:

trajectories:
  - type: curve
    linear_velocity: 1
    angular_velocity: -45
    frame: tracking_point_stabilized
    dt: 0.2
    time: 3
    yaw: heading

Shipped config files

Installed to share/trajectory_library/config/; reference them with $(find-pkg-share trajectory_library)/config/<file>.yaml:

File truncated at 100 lines see the full file