ldrobot-lidar-ros2

ROS 2 package for LDRobot lidar. Based on Nav2 Lifecycle nodes

Get the lidar • YouTube videos • Install • Start the Node • Parameters • RViz2 • Robot integration

This node is designed to work with the DToF 2D Lidar sensors LD19 made by LDRobot.

It can work also with the LD06 model, but no tests have been performed with it. LD06 cannot work outdoor.

LD19	LD06

Get the lidar

My lidar (LD19) comes from the LDRobot kickstarter campaing ended in 2021.

LDRobot then created also an Indiegogo campaign for the LD19.

LDRobot today distributes the Lidar through third-party resellers:

• Waveshare: LD19
• Innomaker: LD19
• Other: Search on Google

The node in action

LD19 Lifecycle	LD19 outdoor

Install the node

The node is designed to work in ROS2 Humble.

Clone the repository in your ROS2 workspace:

cd ~/ros2_ws/src/ #use your current ros2 workspace folder
git clone https://github.com/Myzhar/ldrobot-lidar-ros2.git

Add dependencies:

sudo apt install libudev-dev

Install the udev rules

cd ~/ros2_ws/src/ldrobot-lidar-ros2/scripts/
./create_udev_rules.sh

Build the packages:

cd ~/ros2_ws/
rosdep install --from-paths src --ignore-src -r -y
colcon build --symlink-install --cmake-args=-DCMAKE_BUILD_TYPE=Release

Update the environment variables:

echo source $(pwd)/install/local_setup.bash >> ~/.bashrc
source ~/.bashrc

Start the node

Default parameters

Open a terminal console and enter the following command:

ros2 run ldlidar_node ldlidar_node # <--- not recommended. Better using the launch file 

the ldlidar node is based on the ROS2 lifecycle architecture, hence it starts in the UNCONFIGURED state. To configure the node, setting all the parameters to the default value, trying to estabilish a connection, and activating the scan publisher, the lifecycle services must be called.

Open a new terminal console and enter the following command:

ros2 lifecycle set /lidar_node configure

Transitioning successful is returned if the node is correctly configured and the connection is estabilished, Transitioning failed in case of errors. Look at the node log for information about eventual connection problems.

The node is now in the INACTIVE state, enter the following command to activate:

ros2 lifecycle set /lidar_node activate

The node is now activated and the /ldlidar_node/scan topic of type sensor_msgs/msg/LaserScan is available to be subscribed.

Launch file with YAML parameters

The default values of the parameters of the node can be modified by editing the file ldlidar.yaml.

Open a terminal console and enter the following command to start the node with customized parameters:

ros2 launch ldlidar_node ldlidar.launch.py

The ldlidar.yaml script also starts a robot_state_publisher node that provides the static TF transform of the LDLidar [ldlidar_base->ldlidar_link], and provides the ldlidar description in the /robot_description.

Launch file with YAML parameters and Lifecycle manager

Thanks to the NAV2 project it is possible to launch a lifecycle_manager node that is taking care of processing the state transitions described above.

An example launch file is provided, ldlidar_with_mgr.launch.py, that illustrates how to start a ldlidar_node that loads the parameters from the ldlidar.yaml file, and starts the lifecycle_manager correctly configured with the file lifecycle_mgr.yaml to manage the lifecycle processing:

ros2 launch ldlidar_node ldlidar_with_mgr.launch.py

The ldlidar_with_mgr.launch.py script automatically starts the ldlidar_node by including the ldlidar.launch.py launch file.

Parameters

Following the list of node parameters:

• general.debug_mode: set to true to activate debug messages
• comm.serial_port: the serial port path
• comm.baudrate: the serial port baudrate
• comm.timeout_msec: the serial communication timeout in milliseconds
• lidar.model: Lidar model [LDLiDAR_LD06, LDLiDAR_LD19, LDLiDAR_STL27L]
• lidar.rot_verse: The rotation verse. Use clockwise if the lidar is mounted upsidedown. [CW, CCW]
• lidar.units: distance measurement units [M, CM, MM]
• lidar.frame_id: TF frame name for the lidar
• lidar.bins: set to 0 for dinamic scan size according to rotation speed, set to a fixed value [e.g. 455] for compatibility with SLAM Toolbox
• lidar.range_min: minimum scan distance
• lidar.range_max: maximum scan distance
• lidar.enable_angle_crop: enable angle cropping
• lidar.angle_crop_min: minimum cropping angle
• lidar.angle_crop_max: maximum cropping angle

Display scan on RVIZ2

The launch file ldlidar_rviz2.launch.py starts the ldlidar_node node, the lifecycle_manager node, and a precofigured instance of RViz2 to display the 2D laser scan provided by the LDRobot sensors. This is an example to demonstrate how to correctly setup RViz2 to be used with the ldlidar_node node.

Open a terminal console and enter the following command:

ros2 launch ldlidar_node ldlidar_rviz2.launch.py

Integrate the node in your robot

Follow the following procedure, to integrate the ldlidar_node in a robot configuration:

• Provide a TF transform from base_link to ldlidar_base, that is placed in the center of the base of the lidar scanner. The ldlidar_base -> ldlidar_link transform is provided by the robot_state_publisher started by the ldlidar.launch.py launch file.
• Modify the ldlidar.yaml to match the configuration of the robot.
• Include the ldlidar.launch.py in the bringup launch file of the robot. Follow the provided example.
• Handle lifecycle to correctly start the node. You can use the Nav2 lifecycle_manager, by including it in the bringup launch file. Follow the provided example.
• Enjoy your working system

SLAM Toolbox example

The launch file ldlidar_slam.launch.py shows how to use the node with the SLAM Toolbox package to generate a 2D map for robot navigation.