Waypoint Follower uses NavigateToPose action server to move the robot through a set of waypoints, in order they are provided. Additionally, nav2_waypoint_follower has a plugin interface for specific task executors. Waypoint Task Executor allows to perform custom behaviour when a waypoint is reached (like waiting, taking a picture or doing some complex work). Finally, it has stop_on_failure parameter, that specifies if we should move to a next waypoint if the current one is not reachable.
stop_on_failure (True/False): If false, will continue to next waypoint.
loop_rate (Default: 20): Rate to check for results from current navigation task.
waypoint_task_executor_plugin (string: "wait_at_waypoint"): define tasks the robot should perform upon arriving to a waypoint.
Example (fragment of nav2_params.yaml):
waypoint_follower: ros__parameters: waypoint_task_executor_plugin: "wait_at_waypoint" wait_at_waypoint: plugin: "nav2_waypoint_follower::WaitAtWaypoint" enabled: True waypoint_pause_duration: 0
The nav2_waypoint_follower namespace includes the following plugins:
which corresponds to a standard (ROS2 provided) action that the bot should perform when it reaches a waypoint.
Generally, we need to provide two transformations for Nav2 to work. First is map to odom transform, it is provided by a positioning system (localizetion, mapping, SLAM). Second in odom to base_link, it is provided by an odometry system.
The REP 105 standard defines the required frames and conventions for Nav2 to work. Generally, it states that we should at least have a map to odom to base_link to [sensor_frames] transformations for the robot. To represent time synchronized transformations we use TF2: the time-variant transformations library.