ITS Path Planner ROS 2 Navigation Plugin#

Intelligent Sampling and Two-Way Search (ITS) global path planner is an Intel® patented algorithm.

The ITS Plugin for the ROS 2 Navigation 2 application plugin is a global path planner module that is based on Intelligent sampling and Two-way Search (ITS).

ITS is a new search approach based on two-way path planning and intelligent sampling, which reduces the compute time by about 20x-30x on a 1000 nodes map comparing with the A* search algorithm. The inputs are the 2D occupancy grid map, the robot position, and the goal position.

It does not support continuous replanning.

Prerequisites: Use a simple behavior tree with a compute path to pose and a follow path.

ITS planner inputs:

  • global 2D costmap (nav2_costmap_2d::Costmap2D)

  • start and goal pose (geometry_msgs::msg::PoseStamped)

ITS planner outputs: 2D waypoints of the path

Path planning steps summary:

  1. The ITS planner converts the 2D costmap to either a Probabilistic Road Map (PRM) or a Deterministic Road Map (DRM).

  2. The generated roadmap is saved as a txt file which can be reused for multiple inquiries.

  3. The ITS planner conducts a two-way search to find a path from the source to the destination. Either the smoothing filter or a catmull spline interpolation can be used to create a smooth and continuous path. The generated smooth path is in the form of a ROS 2 navigation message type (nav_msgs::msg).

For customization options, see ITS Path Planner Plugin Customization.

Source Code#

The source code of this component can be found here: ITS-Planner

Getting Started#

Autonomous Mobile Robot provides a ROS 2 Deb package for the application, supported by the following platform:

  • ROS version: humble

Install Deb package#

Install the ros-humble-its-planner Deb package from the Intel® Autonomous Mobile Robot APT repository

sudo apt install ros-humble-its-planner

Run the following script to set environment variables:

source /opt/ros/humble/setup.bash
export TURTLEBOT3_MODEL=waffle_pi
export GAZEBO_MODEL_PATH=$GAZEBO_MODEL_PATH:/opt/ros/humble/share/turtlebot3_gazebo/models

To launch the default ITS planner which is based on differential drive robot, run:

ros2 launch nav2_bringup tb3_simulation_launch.py headless:=False params_file:=/opt/ros/humble/share/its_planner/nav2_params.yaml default_bt_xml_filename:=/opt/ros/humble/share/its_planner/navigate_w_recovery.xml

ITS Planner also supports Ackermann steering; to launch the Ackermann ITS planner run:

ros2 launch nav2_bringup tb3_simulation_launch.py headless:=False params_file:=/opt/ros/humble/share/its_planner/nav2_params_dubins.yaml default_bt_xml_filename:=/opt/ros/humble/share/its_planner/navigate_w_recovery.xml

Note

The above command opens Gazebo* and rviz2 applications. Gazebo* takes a longer time to open (up to a minute) depending on the host’s capabilities. Both applications contain the simulated waffle map, and a simulated robot. Initially, the applications are opened in the background, but you can bring them into the foreground, side-by-side, for a better visual.

  1. Set the robot 2D Pose Estimate in rviz2:

    1. Set the initial robot pose by pressing 2D Pose Estimate in rviz2.

    2. At the robot estimated location, down-click inside the 2D map. For reference, use the robot pose as it appears in Gazebo*.

    3. Set the orientation by dragging forward from the down-click. This also enables ROS 2 navigation.

    ../../../../_images/2d_pose_estimate.png

  2. In rviz2, press Navigation2 Goal, and choose a destination for the robot. This calls the behavioral tree navigator to go to that goal through an action server.

    ../../../../_images/set_navigation_goal.png ../../../../_images/path_created.png

    Expected result: The robot moves along the path generated to its new destination.

  3. Set new destinations for the robot, one at a time.

    ../../../../_images/goal_achived_gazebo_rviz.png

  4. To close this, do the following:

    • Type Ctrl-c in the terminal where you did the up command.

ITS Path Planner Plugin Customization#

The ROS 2 navigation bring-up application is started using the TurtleBot* 3 Gazebo* simulation, and it receives as input parameter its_nav2_params.yaml.

To use the ITS path planner plugin, the following parameters are added in its_nav2_params.yaml:

planner_server:
  ros__parameters:
    expected_planner_frequency: 0.01
    use_sim_time: True
    planner_plugins: ["GridBased"]
    GridBased:
      plugin: "its_planner/ITSPlanner"
      interpolation_resolution: 0.05
      catmull_spline: False
      smoothing_window: 15
      buffer_size: 10
      build_road_map_once: True
      min_samples: 250
      roadmap: "PROBABLISTIC"
      w: 32
      h: 32
      n: 2

ITS Path Planner Plugin Parameters#

catmull_spline:

If true, the generated path from the ITS is interpolated with the catmull spline method; otherwise, a smoothing filter is used to smooth the path.

smoothing_window:

The window size for the smoothing filter (The unit is the grid size.)

buffer_size:

During roadmap generation, the samples are generated away from obstacles. The buffer size dictates how far away from obstacles the roadmap samples should be.

build_road_map_once:

If true, the roadmap is loaded from the saved file; otherwise, a new roadmap is generated.

min_samples:

The minimum number of samples required to generate the roadmap

roadmap:

Either PROBABILISTIC or DETERMINISTIC

w:

The width of the window for intelligent sampling

h:

The height of the window for intelligent sampling

n:

The minimum number of samples that is required in an area defined by w and h

You can modify these values by editing the file below for the default ITS planner, at lines 274-291:

/opt/ros/humble/share/its_planner/nav2_params.yaml

You can modify these values by editing the file below for the Ackermann ITS planner, at lines 274-296:

/opt/ros/humble/share/its_planner/nav2_params_dubins.yaml

Troubleshooting#

For general robot issues, go to Troubleshooting for Autonomous Mobile Robot Tutorials .