Xacro to reduce the code of URDF

Namespace :

<?xml version="1.0"?> <robot xmlns:xacro="http://www.ros.org/wiki/xacro"  name="my_robot">

Usage :

# Constants

1 <xacro:property name="width" value="0.2" />    2 <xacro:property name="bodylen" value="0.6" />    3 <link name="base_link">    4     <visual>    5         <geometry>    6             <cylinder radius="${width}" length="${bodylen}"/>    7         </geometry>    8         <material name="blue"/>    9     </visual>   10     <collision>   11         <geometry>   12             <cylinder radius="${width}" length="${bodylen}"/>   13         </geometry>   14     </collision>   15 </link>

means 

1   <link name="base_link">    2     <visual>    3       <geometry>    4         <cylinder length="0.6" radius="0.2"/>    5       </geometry>    6       <material name="blue"/>    7     </visual>    8     <collision>    9       <geometry>   10         <cylinder length="0.6" radius="0.2"/>   11       </geometry>   12     </collision>   13   </link>

 

# Simple Math

<link name="${witdth*bodylen}"/>

means

<link name="0.12"/>

 

# Macro

Simple Macro

1 <xacro:macro name="default_origin">    2     <origin xyz="0 0 0" rpy="0 0 0"/>    3 </xacro:macro>    4 <xacro:default_origin />

means

1 <origin rpy="0 0 0" xyz="0 0 0"/>

 

Parameterized Macro

1     <xacro:macro name="default_inertial" params="mass">    2         <inertial>    3                 <mass value="${mass}" />    4                 <inertia ixx="1.0" ixy="0.0" ixz="0.0"    5                      iyy="1.0" iyz="0.0"    6                      izz="1.0" />    7         </inertial>    8     </xacro:macro>    1 <xacro:default_inertial mass="10"/>

means

2         <inertial>    3                 <mass value="10" />    4                 <inertia ixx="1.0" ixy="0.0" ixz="0.0"    5                      iyy="1.0" iyz="0.0"    6                      izz="1.0" />    7         </inertial>

 

Parameterized block Macro

1 <xacro:macro name="blue_shape" params="name *shape">    2     <link name="${name}">    3         <visual>    4             <geometry>    5                 <xacro:insert_block name="shape" />    6             </geometry>    7             <material name="blue"/>    8         </visual>    9         <collision>   10             <geometry>   11                 <xacro:insert_block name="shape" />   12             </geometry>   13         </collision>   14     </link>   15 </xacro:macro>   16    17 <xacro:blue_shape name="base_link">   18     <cylinder radius=".42" length=".01" />   19 </xacro:blue_shape>

means

2     <link name="base_link">    3         <visual>    4             <geometry>    5                 <cylinder radius=".42 lenghth=".01" />    6             </geometry>    7             <material name="blue"/>    8         </visual>    9         <collision>   10             <geometry>   11                 <cylinder radius=".42 lenghth=".01" />   12             </geometry>   13         </collision>   14     </link>

 

Examples : 

# Definition of xacro

<xacro:macro name="inertial_box" params="mass x y z *origin">         <inertial>             <xacro:insert_block name="origin"/>             <mass value="${mass}" />             <inertia ixx="${(1/12) * mass * (y*y+z*z)}" ixy="0.0" ixz="0.0"                     iyy="${(1/12) * mass * (x*x+z*z)}" iyz="0.0"                     izz="${(1/12) * mass * (x*x+y*y)}" />         </inertial>     </xacro:macro>

# Usage of xacro

<link name="slider_link">         <visual>             <origin xyz="0 0 0.075" rpy="0 0 0"/>             <geometry>                 <box size="0.5 0.25 0.15" />             </geometry>             <material name="blue" />         </visual>         <collision>             <origin xyz="0 0 0.075" rpy="0 0 0"/>             <geometry>                 <box size="0.5 0.25 0.15" />             </geometry>         </collision>         <xacro:inertial_box mass="0.5" x="0.5" y="0.25" z="0.15">             <origin xyz="0 0 0.075" rpy="0 0 0"/>         </xacro:inertial_box>     </link>

 

 

 

Reference

[1] http://wiki.ros.org/urdf/Tutorials/Using%20Xacro%20to%20Clean%20Up%20a%20URDF%20File

urdf/Tutorials/Using Xacro to Clean Up a URDF File - ROS Wiki

[2] https://github.com/ros/xacro/wiki

GitHub - ros/xacro: Xacro is an XML macro language. With xacro, you can construct shorter and more readable XML files by using m