Galactic to Humble

Moving from ROS 2 Galactic to Humble, a number of stability improvements were added that we will not specifically address here.

Major improvements to Smac Planners

The Smac Planner was significantly improved, of both the 2D and Hybrid-A* implementations, making the paths better, faster, and of higher quality.

  • Collision checker rejects collisions faster and queries the costmap for coordinates less often
  • Zero-copy collision checking object
  • precompute collision checking footprint orientations so no need for trig at runtime
  • Only checking full SE2 footprint when the robot is in the possibly inscribed zones
  • Computing the possibly inscribed zones, or the cost over which some part of the footprint may be in collision with a boundary to check the full footprint. Else, check center cost since promised to not be in a potential collision state
  • Renaming Hybrid-A* planner to SmacPlannerHybrid
  • Precomputing the Reedshepp and Dubin paths offline so at runtime its just a lookup table
  • Replacing the wavefront heuristic with a new, and novel, heuristic dubbed the obstacle heuristic. This computes a Dijkstra’s path taking into account the 8 connected space, as well as weights for the cost at the positions to guide the heuristic into the center of aisle ways. It also downsamples the costmap such that it can reduce the number of expansions by 75% and have a very small error introduced into the heuristic by being off by at most a partial fraction of a single cell distance
  • Improvements to the analytic expansion algorithm to remove the possibility of loops at the end of paths, whenever possible to remove
  • 2D A* travel cost and heuristic improvements to speed up planning times and also increase the path quality significantly
  • Replaced smoother with a bespoke gradient descent implementation
  • Abstract out common utilities of planners into a utils file
  • tuned cost functions
  • precomputed obstacle heuristic using dynamic programming to expand only the minimum number of nodes
  • A caching heuristic setting to enable 25hz planning rates using cached obstacle heuristic values when the goal remains the same
  • Leveraging the symmetry in the dubin and reeds-sheep space to reduce cache size by 50% to increase the window size available for heuristic lookup.
  • Precompute primitives at all orientation bins
  • SmacPlanner2D parameters are now all reconfigurable
The tl;dr of these improvements is:
  • Plans are 2-3x as fast as they were before, well under 200ms for nearly all situations, making it as fast as NavFn and Global Planner (but now kinematically feasible). Typical planning times are sub-100ms without even making use of the caching or downsampling features.
  • Paths are of significantly higher quality via improved smoothers and a novel heuristic that steers the robot towards the center of aisleways implicitly. This makes smoother paths that are also further from obstacles whenever possible.
  • Using caching or downsampler parameterizations, can easily achieve path planning with sub-50ms in nearly any sized space.

Simple (Python) Commander

This PR introduces a new package to Nav2, called the nav2_simple_commander. It is a set of functions in an object, BasicNavigator, which can be used to build Nav2-powered autonomy tasks in Python3 without concerning yourself with the Nav2, ROS 2, or Action server details. It contains a simple API taking common types (primarily PoseStamped) and handles all of the implementation details behind the hood. For example, this is a simple navigation task using this API:

def main():
    rclpy.init()
    navigator = BasicNavigator()

    # Set our demo's initial pose
    initial_pose = PoseStamped()
    ... populate pose ...
    navigator.setInitialPose(initial_pose)

    # Wait for navigation to fully activate
    navigator.waitUntilNav2Active()

    # Go to our demos first goal pose
    goal_pose = PoseStamped()
    ... populate pose ...
    navigator.goToPose(goal_pose)

    while not navigator.isNavComplete():
        feedback = navigator.getFeedback()
        ... do something with feedback ...

        # Basic navigation timeout
        if Duration.from_msg(feedback.navigation_time) > Duration(seconds=600.0):
            navigator.cancelNav()

    result = navigator.getResult()
    if result == NavigationResult.SUCCEEDED:
        print('Goal succeeded!')
    elif result == NavigationResult.CANCELED:
        print('Goal was canceled!')
    elif result == NavigationResult.FAILED:
        print('Goal failed!')

The full API can be found in the README of the package. A number of well commented examples and demos can also be found in the package’s source code at the link prior.

Reduce Nodes and Executors

In order for nav2 to make the best use of ROS 2, we need minimize the number of nodes and executors in nav2, which can improve performance.

This functionality has been discussed in the ticket #816, and carried out in

  • Remove client_node_ in class WaypointFollower : PR2441
  • Remove rclcpp_node_ in class MapSaver : PR2454
  • Remove bond_client_node_ in class LifecycleManager : PR2456
  • Remove node_ in class LifecycleManagerClient : PR2469
  • Remove rclcpp_node_ in class ControllerServer : PR2459, PR2479
  • Remove rclcpp_node_ in class PlannerServer : PR2459, PR2480

Extending the BtServiceNode to process Service-Results

This PR addresses this Ticket and adds a virtual on_completion() function to the BtServiceNode class (here). Similar to the already existing virtual on_wait_for_result() function, it can be overwritten in the child class to react to a respective event with some user-defined operation. The added on_completion() function will be called after the service interaction of the BtServiceNode has been successfully completed.

/**
* @brief Function to perform some user-defined operation upon successful
* completion of the service. Could put a value on the blackboard.
* @return BT::NodeStatus Returns SUCCESS by default, user may override to return another value
*/
virtual BT::NodeStatus on_completion()
{
  return BT::NodeStatus::SUCCESS;
}

The returned BT::NodeStatus will set the current status of the BT-Node. Since the function has access to the results of the service, the returned node-status can depend on those service results, for example. The normal behavior of the BtServiceNode is not affected by introducing the on_completion() function, since the the default implementation still simply returns BT::NodeStatus::SUCCESS, if the service interaction completed successfully.

Spawning the robot in Gazebo

This PR deletes the pkg nav2_gazebo_spawner inside nav2_bringup directory. Instead of nav2_gazebo_spawner the Node spawn_entity.py of gazebo_ros is recomended to spawn the robot in gazebo. Note that

  • gazebo should be started with both libgazebo_ros_init.so and libgazebo_ros_factory.so to work correctly.
  • spawn_entity node could not remap /tf and /tf_static to tf and tf_static in the launch file yet, used only for multi-robot situations. This problem was overcame by adding remapping argument <remapping>/tf:=tf</remapping> <remapping>/tf_static:=tf_static</remapping> under ros2 tag in each plugin which publishs transforms in the SDF file. It is essential to differentiate the tf’s of the different robot.

New parameter use_final_approach_orientation for the 3 2D planners

This PR adds a new parameter use_final_approach_orientation to the 3 2D planners (Theta*, SmacPlanner2D and NavFn), false by default. If true, the last pose of the path generated by the planner will have its orientation set to the approach orientation, i.e. the orientation of the vector connecting the last two points of the path. It allows sending the robot to a position (x,y) instead of a pose (x,y,theta) by effectively ignoring the goal orientation. For example, below, for the same goal with an orientaton pointed left of the screen, use_final_approach_orientation=false (left) and use_final_approach_orientation=true (right)

../_images/use_final_approach_orientation_false.gif ../_images/use_final_approach_orientation_true.gif

SmacPlanner2D and Theta*: fix goal orientation being ignored

This PR fixes the issue of the goal pose orientation being ignored (the end path pose orientation was always set to 0).

SmacPlanner2D, NavFn and Theta*: fix small path corner cases

This PR ensures the planners are not failing when the distance between the start and the goal is small (i.e. when they are on the same costmap cell), and in that case the output path is constructed with a single pose.