Tech Arcanist

VISUALIZE THE ROBOT IN RVIZ2

In this chapter, we will use ROS 2 parameters, robot_state_publisher, joint_state_publisher_gui, and RViz2 together to visualize our robot.

The goal is to:

  • Publish the robot’s URDF model
  • Publish the robot’s joint states
  • Visualize the robot’s TF frames
  • Display the robot meshes
  • Move the wheels using the joint-state sliders
  • Save the RViz2 configuration for use later

Note: This practical uses multiple terminals because each ROS 2 node needs to keep running while we work with RViz2.

Source the workspace

Before running our ROS 2 node, we need to source the workspace.

Open a terminal and go to your workspace:

cd bumperbot_ws

Then source the workspace:

. install/setup.bash

Start robot_state_publisher

robot_state_publisher is a general-purpose ROS 2 node that publishes the robot’s state based on its URDF description.

In our case, we need to provide it with the URDF model of our BumperBot.

Our robot model is written using Xacro, so we use the xacro command to convert it into the URDF representation required by robot_state_publisher.

Run:

ros2 run robot_state_publisher robot_state_publisher --ros-args -p robot_description:="$(xacro /home/techarcanist/bumperbot_ws/src/bumperbot_description/urdf/bumperbot.urdf.xacro)"

Understanding the command

The important part is:

--ros-args -p robot_description:=...

Here we are using a ROS 2 parameter to provide the robot description to the node.

The value is generated by:

$(xacro /home/techarcanist/bumperbot_ws/src/bumperbot_description/urdf/bumperbot.urdf.xacro)

So the process is:

bumperbot.urdf.xacro
        │
        │ xacro
        ▼
     URDF model
        │
        │ robot_description parameter
        ▼
robot_state_publisher
        │
        ▼
ROS 2 topics

The robot_state_publisher node can then use this robot description to publish the information required to visualize the robot.

Keep this terminal running.

Start joint_state_publisher_gui

Open a new terminal. ctrl+shift+O

Source the workspace again:

. install/setup.bash

Now run:

ros2 run joint_state_publisher_gui joint_state_publisher_gui

The joint_state_publisher_gui node provides a graphical interface containing sliders for the movable joints of the robot.

For our robot, the GUI contains sliders for:

wheel_left_joint
wheel_right_joint

These sliders allow us to change the joint positions manually.

Keep this terminal and the GUI running.

Open Another Terminal for RViz2

Now open one more terminal.

Source the workspace again:

. install/setup.bash

Why do we need another terminal?

At this point we have:

Terminal 1
└── robot_state_publisher
Terminal 2
└── joint_state_publisher_gui
Terminal 3
└── RViz2

Each node needs to remain running, so we use separate terminals.

Start RViz2

Now start RViz2:

ros2 run rviz2 rviz2

RViz2 will open with its graphical interface.

At first, the robot may not be visible and you may see an error related to the map frame.

Fix the Fixed Frame Error

The default Fixed Frame in RViz2 is usually:

map

However, our robot does not currently have a map frame.

For this visualization, we should use the robot’s:

base_footprint

Change the Fixed Frame

In the Global Options section:

Fixed Frame: map

change it to:

Fixed Frame: base_footprint

Once this is changed, the frame error should disappear.

Why base_footprint?

base_footprint represents the robot’s base reference frame at ground level.

Since we are visualizing the robot relative to its own base, it is an appropriate fixed frame for this setup.

Add the TF Plugin

Now we will visualize the robot’s TF frames.

Click:

Add

In the plugin selection window, select:

TF

and click:

OK

select TF and click on OK

Visualize the Robot Frames

You should now be able to see frames corresponding to different parts of the robot, such as:

base_footprint
      │
      ▼
  base_link
   /     \
  ▼       ▼
wheels   caster wheels

The TF information represents the position and orientation of the robot’s different links/frames.

The TF plugin also provides an option to display the names of the frames.

Enable:

Show Names

Select Individual Frames

The TF plugin also allows you to control which frames are displayed.

Go to the Frames section of the TF plugin.

You can hide or show individual frames depending on what you want to inspect.

This can be useful when the robot has many frames and the visualization becomes difficult to read.

Add the Robot Model Plugin

The TF plugin shows the robot’s frames, but we also want to see the actual robot meshes.

For this, we need the:

RobotModel

plugin.

Click:

Add

Select:

RobotModel

and click:

OK

Configure the Robot Model

After adding the RobotModel plugin, we need to tell it where the robot description is coming from.

In the RobotModel settings, find:

Description Source

Set it to:

Topic

Then select the robot description topic:

/robot_description

Once /robot_description is selected, RViz2 can use the robot description to display the robot model.

Move the Robot Using Joint State Publisher GUI

We can now use the joint_state_publisher_gui that we started earlier.

For example, moving the:

wheel_right_joint

slider changes the rotation of the right wheel.

Similarly, moving:

wheel_left_joint

changes the rotation of the left wheel.

Save the RViz2 Configuration

At this point, we have configured RViz2 with:

  • base_footprint as the Fixed Frame
  • TF plugin
  • RobotModel plugin
  • /robot_description as the RobotModel source
  • Our desired frame visibility settings

It would be inconvenient to configure all of this again every time we start RViz2.

So we can save the configuration.

Go to:

File → Save Config As

Navigate to:

bumperbot_ws/src/bumperbot_description/rviz

Save the configuration as:

display.rviz

Your file will be located at:

/home/techarcanist/bumperbot_ws/src/bumperbot_description/rviz/display.rviz

Recommended folder structure

bumperbot_description/
├── urdf/
│   └── bumperbot.urdf.xacro
│
└── rviz/
    └── display.rviz

The display.rviz file stores the RViz2 visualization configuration we just created.