How to autonomously navigate toward a detected target

Section

🧭 Navigation - tutorials

🏁 Goal of this tutorial

By the end of this tutorial, you will know how to use any of the sensor’s mounted on your robot to detect a target and autonomously navigate toward it.

Pre-requisites

• You should be able to remotely connect to your robot Set up ROS 2 communication with the robot.

• You should be familiar with ROS’s RViz

• You should have completed the How to detect a target

Warning

Some parts of this tutorial refer to robots equipeed with a specific sensor (Camera or LiDAR). If your robot does not have that sensor, you can skip the corresponding parts.

Navigate toward a Laser Pattern

Warning

This section requires your robot to be equipped with a LiDAR sensor.

In this tutorial, we are going to detect and locate the unique pattern of the PAL Docking Station and make the robot navigate toward it, at a fixed distance of 0.5m.

The easiest way to make the robot detect and navigate toward a target is by using the RViz GUI. This requires that you first establish the communication with the robot as explained in Set up ROS 2 communication with the robot.

Then, in the same terminal that is connected to the robot, you can start RViz with the command:

rviz2 -d /opt/pal/$PAL_DISTRO/share/<ROBOT>_advanced_2dnav/config/rviz/navigation.rviz

Attention

Make sure to replace the <ROBOT> placeholder with the name of your robot (e.g. pmb2, omni_base, ari, etc.). If you are using a TIAGo-Family robot, use the base_type name (either, pmb2 or omni_base).

Otherwise, if you want to use the simulation, you can use the following command:

source /opt/pal/${PAL_DISTRO}/setup.bash
ros2 launch <robot>_gazebo <robot>_gazebo.launch.py navigation:=True advanced_navigation:=True world_name:=pal_office_w_docks

This starts the simulation in a virtual environment with several dockstations available.

Once RViz is running and is connected to the robot or to the simulation, you can trigger the target detection and navigation by following these steps:

1. If not already available, load the PAL Navigation 2 panel in RViz

2. Go to the Target Navigation tab in the PAL Navigation 2 panel

3. Bring the robot close to the target that you want to detect. You can either move it manually using one of the methods described in How to teleoperate your robot or sending an autonomous navigation goal to a pose next to the target, as described in How to Autonomously Navigate while avoiding obstacles.

4. Click on the Select BT button of the Target Navigation tab and from the drop-down menu select the navigate_to_target Behavior Tree and click OK. For the list of all the available behavior trees and the logic they implement, you can refer to 🌳 Target Navigation BT.

5. Click on the Select Detector button of the Target Navigation tab and from the drop-down menu select the pal_nav2_laser_target_detector::LaserTargetDetector Detector and click OK. For the list of all the available detectors and the logic they implement, you can refer to 🧩 Target Detection Plugins.

6. Click on the Set Target ID button of the Target Navigation tab and in the text box insert the ID Number 0 and click OK. This ID corresponds to the PAL Docking Station Laser pattern.

7. Click Start will first trigger the detection of the target using the specified detector and then navigate the robot toward the detected target. It will reach a distance of 0.5m from the target.

This same behavior can be achieved through the Command Line Interface with the command:

ros2 action send_goal /navigate_to_target pal_nav2_msgs/action/NavigateToTarget "target_id: 0
detector: 'laser_target_detector'
behavior_tree: 'navigate_to_target'"

Navigate toward an ArUCO Marker

Warning

This section requires your robot to be equipped with a Camera sensor.

In this example, the ArUco Target Detector is used to detect an ArUco Marker placed on the wall (ID 20) and making the robot navigate towards it.

The easiest way to make the robot detect and navigate toward a target is by using the RViz GUI. This requires that you first establish the communication with the robot as explained in Set up ROS 2 communication with the robot.

Then, in the same terminal that is connected to the robot, you can start RViz with the command:

rviz2 -d /opt/pal/$PAL_DISTRO/share/<ROBOT>_advanced_2dnav/config/rviz/navigation.rviz

Attention

Make sure to replace the <ROBOT> placeholder with the name of your robot (e.g. tiago, omni_base, tiago_pro, etc.).

Otherwise, if you want to use the simulation, you can use the following command:

source /opt/pal/${PAL_DISTRO}/setup.bash
ros2 launch <robot>_gazebo <robot>_gazebo.launch.py navigation:=True advanced_navigation:=True world_name:=pal_office_w_aruco

This starts the simulation in a virtual environment with several dockstations available.

Once RViz is running and is connected to the robot or to the simulation, you can trigger the target detection and navigation by following these steps:

1. If not already available, load the PAL Navigation 2 panel in RViz

2. Go to the Target Navigation tab in the PAL Navigation 2 panel

3. Bring the robot close to the target that you want to detect. You can either move it manually using one of the methods described in How to teleoperate your robot or sending an autonomous navigation goal to a pose next to the target, as described in How to Autonomously Navigate while avoiding obstacles.

4. Click on the Select BT button of the Target Navigation tab and from the drop-down menu select the navigate_to_target Behavior Tree and click OK. For the list of all the available behavior trees and the logic they implement, you can refer to 🌳 Target Navigation BT.

5. Click on the Select Detector button of the Target Navigation tab and from the drop-down menu select the pal_nav2_laser_target_detector::ArucoTargetDetector Detector and click OK. For the list of all the available detectors and the logic they implement, you can refer to 🧩 Target Detection Plugins.

6. Click on the Set Target ID button of the Target Navigation tab and in the text box insert the ID Number 20 and click OK. This value corresponds to the ID of the ArUCO marker that has to be detected.

7. Click Start will first trigger the detection of the target using the specified detector and then navigate the robot toward the detected target. It will reach a distance of 0.5m from the target.

This same behavior can be achieved through the Command Line Interface with the command:

ros2 action send_goal /navigate_to_target pal_nav2_msgs/action/NavigateToTarget "target_id: 20
detector: 'aruco_target_detector'
behavior_tree: 'navigate_to_target'"

Next steps

• If you want to learn more about the target detection system, you can refer to 📡 Target Detection.

• If you want to learn how to create a new Target Detector, you can refer to 🧩 Target Detection Plugins.