ldrobot-lidar-ros2

ROS2 package for LDRobot lidar. Based on ROS2 Lifecycle nodes

Install • Start the Node • Parameters • RViz2 • Robot integration • Todo

Install the node

The node has bee tested with ROS2 Foxy on Ubuntu 20.04.

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

Build the packages:

cd ..
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

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.direct_serial: set to false to use the USB <-> UART converter, true for direct UART connection
• comm.serial_port: the serial port path if using direct UART connection
• lidar.frame_id: TF frame name for the lidar
• lidar.rot_verse: 0 -> CLOCKWISE / 1 -> COUNTERCLOCKWISE [ROS STANDARD]
• lidar.units: 0 -> MILLIMETERS / 1 -> CENTIMETERS / 2 -> METERS [ROS STANDARD]
• lidar.qos_history: 0 -> RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT / 1 -> RMW_QOS_POLICY_HISTORY_KEEP_LAST / 2 -> RMW_QOS_POLICY_HISTORY_KEEP_ALL
• lidar.qos_depth: History depth in case of RMW_QOS_POLICY_HISTORY_KEEP_LAST
• lidar.qos_reliability: 0 -> RMW_QOS_POLICY_RELIABILITY_SYSTEM_DEFAULT / 1 -> RMW_QOS_POLICY_RELIABILITY_RELIABLE / 2 -> RMW_QOS_POLICY_RELIABILITY_BEST_EFFORT
• lidar.qos_durability: 0 -> RMW_QOS_POLICY_DURABILITY_SYSTEM_DEFAULT / 1 -> RMW_QOS_POLICY_DURABILITY_TRANSIENT_LOCAL / 2 -> RMW_QOS_POLICY_DURABILITY_VOLATILE

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

TODO

• Direct serial connection without USB<->Serial converter