Contents
Overview
This package contains a number of XML specifications for robot models, sensors, scenes, etc. Each XML specification has a corresponding parser in one or more languages.
XML Description |
C++ |
Python |
XML Schema |
|
Model |
||||
Sensor |
|
|
Components
New in Hydro A number of different packages and components make up urdf. The following diagram attempts to explain the relationship between these components:
Current Status of URDF Components in Hydro:
- The core URDF parser and data structures (urdfdom, urdfdom_headers) have been pushed upstream into stand alone (no ROS-dependencies) software packages that will in the future be released into Ubuntu completely separate from ROS.
- There is now a distinction between a URDF file and a URDF data structure. A URDF file follows the XML format as described on the ros.org wiki. A URDF data structure is a set of generic classes that various formats (currently URDF and Collada) can be parsed into.
- A new plugin abstraction layer (urdf_parser_plugin) allows the URDF data structures to be populated with various file formats (currently URDF and Collada)
- The ROS packages urdf_parser and urdf_interface have been deprecated in Groovy and removed in Hydro.
Getting Started
There is large set of tutorials on how to build up your own robot models using the URDF specification. Check out the urdf/Tutorials page.
We also developed a macro language called xacro to make it easier to maintain the robot description files, increase their readability, and to avoid duplication in the robot description files.
Examples
See this page for a list of robots described by a URDF model.
Tools
Verification
A command line tool check_urdf attempts to parse a file as a URDF description, and either prints a description of the resulting kinematic chain, or an error message.
For example, to run this tool on the pr2 urdf, first create the urdf file by running:
rosrun xacro xacro.py `rospack find pr2_description`/robots/pr2.urdf.xacro -o /tmp/pr2.urdf
New in Indigo
Then run the check by running:
Note: You may need to run sudo apt-get install liburdfdom-tools.
check_urdf pr2.urdf
New in Hydro
Then run the check by running:
rosrun urdfdom check_urdf /tmp/pr2.urdf
and you should see something resembling:robot name is: pr2 ---------- Successfully Parsed XML --------------- root Link: base_footprint has 1 child(ren) child(1): base_link child(1): base_laser_link child(2): bl_caster_rotation_link child(1): bl_caster_l_wheel_link child(2): bl_caster_r_wheel_link child(3): br_caster_rotation_link child(1): br_caster_l_wheel_link child(2): br_caster_r_wheel_link child(4): fl_caster_rotation_link child(1): fl_caster_l_wheel_link child(2): fl_caster_r_wheel_link child(5): fr_caster_rotation_link child(1): fr_caster_l_wheel_link child(2): fr_caster_r_wheel_link child(6): torso_lift_link child(1): head_pan_link child(1): head_tilt_link child(1): head_plate_frame child(1): sensor_mount_link child(1): double_stereo_link child(1): narrow_stereo_link ...
Visualization
Visual Studio Code has a ROS extension that supports URDF visualization.
To get a graphviz diagram of your urdf file, do the following:
New in Indigo In Indigo, the urdf_to_graphiz tool has moved to the liburdfdom-tools package. You may need to run sudo apt-get install liburdfdom-tools if you can't use urdf_to_graphiz
urdf_to_graphiz pr2.urdf
New in Hydro
urdf_to_graphiz pr2.urdf
The result is a file called pr2.pdf that looks something like this:
Creating URDF
URDF is XML, which is a text format. So you can create the files in any text editor. An IDE with good XML support is recommended.
If there already exists a CAD model of the robot, there are some tools that can be used to convert the CAD model to URDF. Here is a non-exhaustive list:
Known Issues
- Sensor model information is not included (except in gazebo extensions for simulated sensors).
