Gazebo launch tutorial

Gazebo Launch is used to run and manage plugins and programs. A configuration script can be used to specify which programs and plugins to execute. Alternatively, individual programs and plugins can be run from the command line.

In this tutorial we will explain the configuration scripts in the examples directory.

We can do many things:

• Run multiple executable commands
• Spawn a robot into simulation with plugins

To run a script use

gz launch LAUNCH_FILE_NAME

Launch files

Every script starts with these two tags, which specify the xml version and gz version.

<?xml version="1.0"?>
<gz version='1.0'>

Multiple executable commands

We can run multiple commands from one file.

Take a look at the sim.gzlaunch launch file. This script runs the Gazebo server and Gazebo client. We need to just write the command in the command tag.

<executable name='sim-server'>
    <command>gz sim -s</command>
</executable>

Spawn a robot into simulation with plugins

Now take a look at the factory.gzlaunch launch file. We defined a SimFactory plugin under which we included an X2 UGV robot and added the DiffDrive plugin to control the robot. We also added the JointStatePublisher plugin which publishes the robot state information.

First launch Gazebo in an empty world

gz sim -v 4 empty.sdf

In another terminal, spawn the robot into simulation using gz-launch

gz launch -v 4 factory.gzlaunch

Launch simulation with plugins in separate processes

The sim_plugins.gzlaunch launch file loads some plugins and also starts simulation. The joystick plugin will be launched in its own process and will read from a joystick device and output data onto a topic. The JoyToTwist plugin also launches into a separate process and transforms a joystick message to a twist message. Finally, The SimServer plugin launches the Gazebo server.

The script can take a world as an argument. To run this script.

gz launch sim_plugins.gzlaunch [worldName:=<worldName>]

The [worldName] command line argument is optional. If left blank, or not specified, then "diff_drive" is used for the world name.

Example to load the shapes.sdf:

gz launch sim_plugins.gzlaunch worldName:=shapes

‍Note: This example requires that you have a joystick plugged in. If you don't have one, you will see some error messages complaining that it can not find any joystick / input devices and the plugin will fail to load. This is expected.

Launch file lookup

There is a lookup process happening if the specified file is not an absolute path. It searches for a file with the given name in paths as follows:

1. current directory

1. all paths specified in environment variable GZ_LAUNCH_CONFIG_PATH

1. a hardcoded install location (usually /usr/share/gz/gz-launchN/configs/)

The GZ_LAUNCH_CONFIG_PATH environment variable can contain either a single path or a path list (new since 2.2.2). Path list is a colon-separated (on UNIX) or semicolon-separated (on Windows) list of absolute paths.