URDF Robot Model + RViz Visualisation¶

Concept¶

URDF (Unified Robot Description Format) is an XML file describing your robot's geometry, joints, and links. RViz is ROS 2's 3D visualisation tool. The robot_state_publisher node reads the URDF and broadcasts transforms.

Install Dependencies¶

sudo apt install ros-humble-urdf-tutorial ros-humble-joint-state-publisher-gui -y

Create the URDF File¶

Save as ~/ROBOT/src/robot_pkg/robot_pkg/my_robot.urdf:

<?xml version="1.0"?>
<robot name="simple_robot">

  <!-- Base link (blue box) -->
  <link name="base_link">
    <visual>
      <geometry>
        <box size="0.5 0.3 0.1"/>
      </geometry>
      <material name="blue">
        <color rgba="0 0 1 1"/>
      </material>
    </visual>
  </link>

  <!-- Left Wheel (black cylinder) -->
  <link name="left_wheel">
    <visual>
      <geometry>
        <cylinder radius="0.05" length="0.04"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
  </link>

  <!-- Right Wheel (black cylinder) -->
  <link name="right_wheel">
    <visual>
      <geometry>
        <cylinder radius="0.05" length="0.04"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
  </link>

  <!-- Left Wheel Joint -->
  <joint name="left_wheel_joint" type="continuous">
    <parent link="base_link"/>
    <child  link="left_wheel"/>
    <origin xyz="0.15 0.17 0" rpy="1.5707 0 0"/>
    <axis xyz="0 0 1"/>
  </joint>

  <!-- Right Wheel Joint -->
  <joint name="right_wheel_joint" type="continuous">
    <parent link="base_link"/>
    <child  link="right_wheel"/>
    <origin xyz="0.15 -0.17 0" rpy="1.5707 0 0"/>
    <axis xyz="0 0 1"/>
  </joint>

</robot>

Visualise in RViz¶

Terminal 1 — Publish robot description

ros2 run robot_state_publisher robot_state_publisher   --ros-args -p robot_description:="$(cat ~/ROBOT/src/robot_pkg/robot_pkg/my_robot.urdf)"

Terminal 2 — Joint state publisher GUI (spin the wheels)

ros2 run joint_state_publisher_gui joint_state_publisher_gui

Terminal 3 — Open RViz

rviz2

RViz Configuration Steps

In the Global Options panel, set Fixed Frame to base_link
Click Add (bottom left)
Select RobotModel from the list
In the RobotModel panel, set the Description Topic to /robot_description

Expected Result¶

RViz will show a blue rectangular box (the base) with two black cylinders (the wheels) attached at its sides. The Joint State Publisher GUI lets you rotate the wheels interactively.

URDF Quick Reference¶

Element	Purpose
`<link>`	A rigid body part of the robot
`<joint>`	Connects two links; defines motion type
`<visual>`	What the link looks like in RViz
`<geometry>`	Shape: box, cylinder, sphere, mesh
`<origin>`	Position & orientation (xyz rpy)