# Gazebo Simulation

WARNING

Gazebo was previously known as "Gazebo Ignition" (while Gazebo Classic was previously known as Gazebo). See the official blog post (opens new window) for more information.

Gazebo (opens new window) is an open source robotics simulator. It supersedes the older Gazebo Classic simulator, and is the only supported version of Gazebo for Ubuntu 22.04 and onwards.

Supported Vehicles: Quadrotor, Plane, VTOL

Note

See Simulation for general information about simulators, the simulation environment, and simulation configuration (e.g. supported vehicles).

# Installation (Ubuntu Linux)

Gazebo is installed by default on Ubuntu 22.04 as part of the development environment setup: Ubuntu Dev Environment Setup > Simulation and NuttX (Pixhawk) Targets

If you want to use Gazebo on Ubuntu 20.04 you can install it manually after following the normal setup process (installing gz-garden will uninstall Gazebo-Classic!):

sudo wget https://packages.osrfoundation.org/gazebo.gpg -O /usr/share/keyrings/pkgs-osrf-archive-keyring.gpg
echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/pkgs-osrf-archive-keyring.gpg] http://packages.osrfoundation.org/gazebo/ubuntu-stable $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/gazebo-stable.list > /dev/null
sudo apt-get update
sudo apt-get install gz-garden

# Running the Simulation

Gazebo SITL simulation can be conveniently run through a make command as shown below:

cd /path/to/PX4-Autopilot
make px4_sitl gz_x500

This will run both the PX4 SITL instance and the Gazebo client. Note that all gazebo make targets have the prefix gz_.

Note

If make px4_sitl gz_x500 gives the error ninja: error: unknown target 'gz_x500' then run make distclean to start from a clean slate, and try running make px4_sitl gz_x500 again.

The supported vehicles and make commands are listed below.

Vehicle Command PX4_SYS_AUTOSTART
Quadrotor(x500) make px4_sitl gz_x500 4001
Quadrotor(x500) with Depth Camera make px4_sitl gz_x500_depth 4002
Quadrotor(x500) with Vision Odometry make px4_sitl gz_x500_vision 4005
VTOL make px4_sitl gz_standard_vtol 4004
Plane make px4_sitl gz_rc_cessna 4003
Advanced Plane make px4_sitl gz_advanced_plane 4008

WARNING

(09.11.2023) The Advanced Lift Drag Plugin that is required to run the Advanced Plane is not yet part of the Gazebo distribution, so the Advanced Plane will not yet fly: PX4-Autopilot Github issues page (opens new window).

As a workaround to enable Advanced Plane, you can compile the gz-sim library from Gazebo source code (opens new window), go into the build/lib directory, copy out the advanced lift drag plugin .so file (depending on the exact Gazebo Version this is called something along the lines of libgz-sim7-advanced-lift-drag-system.so), and paste this into the ~/.gz/sim/plugins folder.

The commands above launch a single vehicle with the full UI. QGroundControl should be able to automatically connect to the simulated vehicle.

# Headless Mode

You might want to run Gazebo in "headless mode" (without the Gazebo GUI) as it uses fewer resources, and does not rely on your system having a graphics card that properly supports OpenGL rendering. This makes it faster to load and run, and for many simple use cases may be all you need.

The simulation can be run in headless mode by prefixing the command with the HEADLESS=1 environment variable:

HEADLESS=1 make px4_sitl gz_x500

# Specify World

The simulation can be run inside a particular world by concatenating the desired world to the name of the desired vehicle. For example, to run the windy world with the x500 vehicle you can specify:

make px4_sitl gz_x500_windy

You can also specify the world using the PX4_GZ_WORLD environment variable:

PX4_GZ_WORLD=windy make px4_sitl gz_x500

The supported worlds are listed below.

World Command Description
default make px4_sitl * Empty world (a grey plane)
windy make px4_sitl *_windy Empty world with wind enabled

WARNING

Note that if no world is specified, PX4 will use the default world. However you must not explicitly specify _default on the model as this will prevent PX4 from launching. In other words, use make px4_sitl gz_x500 instead of make px4_sitl gz_x500_default for the default.

# Usage/Configuration Options

The startup pipeline allows for highly flexible configuration. In particular, it is possible to:

  • Start a new simulation with an arbitrary world or attach to an already running simulation.
  • Add a new vehicle to the simulation or link a new PX4 instance to an existing one.

These scenarios are managed by setting the appropriate environment variables.

# Syntax

The startup syntax takes the form:

ARGS ./build/px4_sitl_default/bin/px4

where ARGS is a list of environment variables including:

  • PX4_SYS_AUTOSTART (Mandatory): Sets the airframe autostart id of the PX4 airframe to start.

  • PX4_GZ_MODEL_NAME: Sets the name of an existing model in the gazebo simulation. If provided, the startup script tries to bind a new PX4 instance to the Gazebo resource matching exactly that name.

    • The setting is mutually exclusive with PX4_GZ_MODEL.
  • PX4_GZ_MODEL: Sets the name of a new Gazebo model to be spawned in the simulator. If provided, the startup script looks for a model in the Gazebo resource path that matches the given variable, spawns it and binds a new PX4 instance to it.

    • The setting is mutually exclusive with PX4_GZ_MODEL_NAME.

    Note

    If both PX4_GZ_MODEL_NAME and PX4_GZ_MODEL are not given, then PX4 looks for PX4_SIM_MODEL and uses it as an alias for PX4_GZ_MODEL. However, this prevents the use of PX4_GZ_MODEL_POSE.

  • PX4_GZ_MODEL_POSE: Sets the spawning position and orientation of the model when PX4_GZ_MODEL is adopted. If provided, the startup script spawns the model at a pose following the syntax "x,y,z,roll,pitch,yaw", where the positions are given in metres and the angles are in radians.

    • If omitted, the zero pose [0,0,0,0,0,0] is used.
    • If less then 6 values are provided, the missing ones are fixed to zero.
    • This can only be used with PX4_GZ_MODEL (not PX4_GZ_MODEL_NAME).
  • PX4_GZ_WORLD: Sets the Gazebo world file for a new simulation. If it is not given, then default (opens new window) is used.

  • PX4_SIMULATOR=GZ: Sets the simulator, which for Gz must be gz.

The PX4 Gazebo worlds and and models databases can be found on Github here (opens new window). They are added to the Gazebo search PATH by gz_env.sh.in (opens new window) during the simulation startup phase.

Note

gz_env.sh.in is compiled and made available in $PX4_DIR/build/px4_sitl_default/rootfs/gz_env.sh

# Examples

Here are some examples of the different scenarios covered above.

  1. Start simulator + default world + spawn vehicle at default pose

    PX4_SYS_AUTOSTART=4001 PX4_SIM_MODEL=gz_x500 ./build/px4_sitl_default/bin/px4
    
  2. Start simulator + default world + spawn vehicle at custom pose (y=2m)

    PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL_POSE="0,2" PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4
    
  3. Start simulator + default world + link to existing vehicle

    PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL_NAME=x500 ./build/px4_sitl_default/bin/px4
    

# Adding New Worlds and Models

New worlds files can simply be copied into the PX4 Gazebo world directory (opens new window).

To add a new model:

  1. Add an sdf file in the PX4 Gazebo model directory (opens new window).

  2. Define an airframe configuration file.

  3. Define the default parameters for Gazebo in the airframe configuration file (this example is from x500 quadcopter (opens new window)):

    PX4_SIMULATOR=${PX4_SIMULATOR:=gz}
    PX4_GZ_WORLD=${PX4_GZ_WORLD:=default}
    PX4_SIM_MODEL=${PX4_SIM_MODEL:=<your model name>}
    
    • PX4_SIMULATOR=${PX4_SIMULATOR:=gz} sets the default simulator (Gz) for that specific airframe.

    • PX4_GZ_WORLD=${PX4_GZ_WORLD:=default} sets the default world (opens new window) for that specific airframe.

    • Setting the default value of PX4_SIM_MODEL lets you start the simulation with just:

      PX4_SYS_AUTOSTART=<your new airframe id> ./build/px4_sitl_default/bin/px4
      

Note

As long as the world file and the model file are in the Gazebo search path GZ_SIM_RESOURCE_PATH it is not necessary to add them to the PX4 world and model directories. However, make px4_sitl gz_<model>_<world> won't work with them.

# PX4-Gazebo Time Synchronization

Unlike the Gazebo Classic and jMAVSim simulators, PX4 and Gazebo do not implement a lockstep mechanism. During Gazebo simulations PX4 subscribes to the Gazebo \clock topic and uses it as clock source. This guarantees that PX4 will always wait for Gazebo before moving forward in time, even if Gazebo is running with real time factors different from 1. Note, however, that as the lockstep is missing, Gazebo will never wait for PX4 to finish its computations. In the worst case scenario, PX4 can completely go offline and Gazebo will keep running, with obvious crashes of the simulated drone.

# Multi-Vehicle Simulation

Multi-Vehicle simulation is supported on Linux hosts.

For more information see: Multi-Vehicle Simulation with Gazebo

# Further Information