Rviz2 Displays

Let's learn about RViz2 Displays and setting it up for Laser scans

RViz2 Screen Layout

RViz has 3 main panels by default, and you can add additional panels to suit your needs (it’s very flexible).

In the screenshot above you can see the main areas of the screen:

1. The Displays panel (outlined in Red)
2. The Main Camera Display (outlined in Blue)
3. The Views panel (outlined in Green)

RPLidar Laser scanner

The SlamTec RPLidar A1 is an affordable laser scanner, ideal for use with robotics, and costs less than £99. We will use this in our tutorial.

Adding our LiDAR Laser Scan

To view our LiDAR data in Rviz2 we need to do a couple of actions:

• Download and compile the RPLidar_ros code
• Start the RPLidar node
• Start a transformation node to translate the laser_scan coordinates to the World coordinates
• Start rviz2 and add the laser_scan display

Download and compile the RPLidar_ros code

• Download RPLidar code - From the Raspberry Pi terminal, type:

cd ~/cubie-1
git clone https://github.com/babakhani/rplidar_ros2

Slamtec now maintain their own ROS 2 driver, sllidar_ros2, which also supports their newer LiDARs. It’s started with ros2 launch sllidar_ros2 view_sllidar_a1_launch.py.

The rplidar_ros2 folder needs to be inside the cubie-1 folder, which appears as /ros2 inside the container.

• Compile the RPLidar code - From the container, type:

cd /ros2/rplidar_ros2
colcon build
source install/setup.bash

Start the RPLidar node

We can now start the Laser scanner node.

• Start a new container terminal session - from the Raspberry Pi terminal, type:

cd ~/cubie-1/docker-full
docker compose exec ros2 bash

• Start the Laser Scanner - from the container, type:

cd /ros2/rplidar_ros2
source install/setup.bash
ros2 run rplidar_ros rplidar_composition

The RPLidar will momentarily stop and then restart, and you will see some output on the terminal showing that the LiDAR is now up and running

Check the scan data topic exists

We can check that the /scan topic exists by using the ros2 topic list command. Let’s open a new terminal and check we can see it.

• Start a new container terminal session - from the Raspberry Pi terminal, type:

cd ~/cubie-1/docker-full
docker compose exec ros2 bash

• Ros2 topic list - from the container, type:

ros2 topic list

There should be three topics listed:

/parameter_events
/rosout
/scan

If the /scan topic is visible, this means the LiDAR is successfully sending data to the Ros topic named /scan.

Start RViz2

Let’s start RViz2.

• Start RViz2 - from the container, type:

rviz2

We will configure RViz in the next section.

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