Explaining the URDF file

When we check the code, we can add a <robot> tag at the top of the description:

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

The <robot> tag defines the name of the robot that we are going to create. Here, we named the robot pan_tilt.

If we check the sections after the <robot> tag definition, we can see link and joint definitions of the pan-and-tilt mechanism:

  <link name="base_link"> 
    <visual> 
      <geometry> 
      <cylinder length="0.01" radius="0.2"/> 
      </geometry> 
      <origin rpy="0 0 0" xyz="0 0 0"/> 
      <material name="yellow"> 
        <color rgba="1 1 0 1"/> 
      </material> 
    </visual> 
  </link> 

The preceding code snippet is the base_link definition of the pan-and-tilt mechanism. The <visual> tag describes the visual appearance of the link, which is shown on the robot simulation. We can define the link geometry (cylinder, box, sphere...