Spawn URDF

This tutorial will cover how to spawn a URDF model in Gazebo Sim. URDF files are often used in ROS to represent robot models. While SDF can describe a world with multiple robot models, URDF can only describe one robot model. More information about URDF can be found at https://wiki.ros.org/urdf.

Obtaining a URDF file

This tutorial assumes that the reader already has a URDF file that they’d like to load into Gazebo Sim. If you are looking for a URDF file to use, you can use the rrbot.urdf that was preprocessed for you. The rrbot robot model is from the gazebo_ros_demos package. You could also use one of the examples listed at https://wiki.ros.org/urdf/Examples.

If you have a xacro representation of a robot model, you can turn the xacro file into a URDF file using the xacro package: see this tutorial for more information.

Spawning the URDF

To spawn a URDF model in Gazebo Sim, we will start a world and make use of the world’s create service, which uses the EntityFactory message type.

Start by launching an empty world in Gazebo Sim:

ign gazebo empty.sdf

You should see a window that looks like this:

In another terminal, get the list of available services by running ign service -l. Look for a create service. You should see this service in the list:

/world/empty/create

We can double-check that this is the service we want to use by running ign service -is /world/empty/create. This will show us the service’s request and response message types:

ignition.msgs.EntityFactory, ignition.msgs.Boolean

Now that we have found the service that has an EntityFactory request type, we can call this service and pass the URDF file to the service’s request so that the robot represented by this URDF file is spawned in the Gazebo Sim world. We do this by setting the desired URDF file to the sdf_file_name field of the EntityFactory request message. The libsdformat library will then internally convert the URDF file to an SDF representation, and load this into the running world.

The following command spawns the URDF file model.urdf into the Gazebo Sim world as a model named urdf_model:

ign service -s /world/empty/create --reqtype ignition.msgs.EntityFactory --reptype ignition.msgs.Boolean --timeout 1000 --req 'sdf_filename: "/path/to/model.urdf", name: "urdf_model"'

If model.urdf is the URDF representation of rrbot.xacro in the gazebo_ros_demos package, executing the service call above should result in a simulation that now looks like this:

We can now play the simulation to make sure that the loaded URDF model behaves as expected: