ROS2 & PX4 Precision Landing with ArUco Markers

Master the integration of ROS2, PX4, and OpenCV to achieve precision landing using ArUco marker detection. This tutorial delves into how to leverage ROS2’s robust communication framework and PX4’s flight control system to implement highly accurate landings for autonomous drones. You’ll learn how to configure your environment, process camera feeds, and detect ArUco markers in real-time, enabling your drone to land precisely at designated targets. Whether you’re new to drone development or an experienced engineer, this guide provides a step-by-step approach to achieving reliable precision landing with seamless integration into your ROS2 and PX4 projects.

ArUco Markers

Aruco markers are square fiducial markers used in computer vision for tasks like pose estimation, camera calibration, and augmented reality (AR). Each marker has a unique binary pattern inside a black border, allowing it to be easily detected and identified. They help in determining the position and orientation of cameras or objects in a scene, making them valuable in robotics, navigation, and AR applications. https://docs.opencv.org/4.x/d5/dae/tutorial_aruco_detection.html

Video Walkthrough

Watch the video on YouTube

Prerequisites

• Ubuntu 22.04
• ROS2 Humble
• PX4 Autopilot with an ArUco Marker and downward facing camera
• Micro XRCE-DDS Agent
• QGroundControl Daily Build
• OpenCV 4.10.0
• ROS_GZ bridge

You can find the required instructions collected below

https://docs.px4.io/main/en/ros2/user_guide.html https://docs.qgroundcontrol.com/master/en/qgc-user-guide/releases/daily_builds.html

You need the lates PX4-Autopilot, that will contain the required drone with the downward facing camera and the world that has the aruco marker in it To get ros_gz bridge

sudo apt install ros-humble-ros-gzgarden

https://github.com/gazebosim/ros_gz

For the OpenCV part follow the instructions below

Usage

Setup the Workspace

Make sure you source ROS2 Humble in the terminal you are using.

source /opt/ros/humble/setup.bash

OR Just add the line above to your bashrc, in that case it is going to be sourced every time you open a terminal.

nano ~/.bashrc

Navigate to the directory you would like to place the worskpace and then run the following

git clone https://github.com/ARK-Electronics/tracktor-beam.git

Then navigate into the workspace:

cd tracktor-beam

Install OpenCV from source

./install_opencv.sh 

Install the submoduls

git submodule update --init --recursive

Build the workspace

colcon build

After this runs, we do not need to build the whole workspace again, you can just build the individual packages you have modified

colcon build --packages-select precision_land

Source the workspace

source install/setup.bash 

Run the example

Run the simulation environment

Launch PX4 sim

make px4_sitl gz_x500_mono_cam_down_aruco

Launch micro dds

MicroXRCEAgent udp4 -p 8888

Launch the ros_gz_bridge for getting the camera topic

ros2 run ros_gz_bridge parameter_bridge /camera@sensor_msgs/msg/Image@gz.msgs.Image

Launch the ros_gz_bridge for getting the camera info topic (this is how we get camera intrinsics)

ros2 run ros_gz_bridge parameter_bridge /camera_info@sensor_msgs/msg/CameraInfo@gz.msgs.CameraInfo

Launch the ros2 nodes (aruco_tracker)

cd tracktor-beam/
source install/setup.bash 
ros2 run aruco_tracker aruco_tracker 

OR Launch file with the bridges:

source install/setup.bash
ros2 launch aruco_tracker aruco_tracker.launch.py 

View the video (/image_proc is the annoted image)

ros2 run rqt_image_view rqt_image_view

Launch the ros2 nodes (precision_land)

cd tracktor-beam/
source install/setup.bash 
ros2 run precision_land precision_land

OR Launch file with the params:

ros2 launch precision_land precision_land.launch.py

Once the nodes are running the Precision Land mode is going to show up in QGC

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Questions

Message Patrik Dominik Pordi on the ARK Electronics / Dronecode Foundation Discord for questions or email me at patrik@arkelectron.com

ARK Electronics Discord

Additional resources

LinuxCheatSheet

ROS2CheatSheet

CMakeBasics

Hardware

Prerequisites

• Ubuntu 22.04
• ROS2 Humble
• Drone with downward facing camera
• Micro XRCE-DDS Agent
• QGroundControl
• OpenCV 4.10.0
• Camera node: I use an usb camera, there is a ROS2 package already out there for it: https://github.com/ros-drivers/usb_cam.git

You can either run the the nodes or turn them into a service, that starts at boot:

Normal run

Service

First, you need to move your service file to the /etc/systemd/system/ directory, where systemd can find it. Replace myservice.service with the actual name of your service file.

Ensure that the service file has the correct permissions. Typically, it should be readable by all users:

sudo chmod 644 /etc/systemd/system/myservice.service

After copying the service file, reload the systemd daemon to recognize the new service:

sudo systemctl daemon-reload

Start the service using systemctl:

sudo systemctl start myservice

If you want the service to start automatically on boot, enable it:

sudo systemctl enable myservice

Verify that the service is running correctly:

sudo systemctl status myservice