# 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 using a make command as shown below:

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

This runs both the PX4 SITL instance and the Gazebo client.

The supported vehicles and make commands are listed below. Note that all gazebo make targets have the prefix gz_.

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

All vehicle models (and worlds) are included as a submodule from the Gazebo Models Repository repository.

WARNING

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#22337 (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.

# Standalone Mode

Another way that Gazebo SITL can be connected is in standalone mode. In this mode PX4 SITL and Gazebo are started separately in their own terminals. By default these terminals are on the same host, but you can also connect SITL and Gazebo instances running on any two devices on the network (or even different networks if you use a VPN to connect them).

You start PX4 in standalone mode by prefixing the make command with PX4_GZ_STANDALONE=1:

cd /path/to/PX4-Autopilot
PX4_GZ_STANDALONE=1 make px4_sitl gz_x500

PX4 SITL will then wait until it detects an instance of gz-server, and then connect to it.

Note

If you have not yet started gz-server when you run the make command, you will see the following warning until gazebo has been started and an instance of gz-server is detected by PX4:

WARN [gz bridge] Service call timed out as Gazebo has not been detected

The simplest way to start the simulation is to use the Python script simulation-gazebo (opens new window), which can be found in the Gazebo Models Repository repository. This can be used to launch a gz-server instance with any supported world and vehicle.

The script can be used without installing any additional dependencies, and will fetch the supported PX4 models and worlds on first use (by default) and save them to ~/.simulation-gazebo. If called again the script will use this directory to get models and worlds. Therefore if you want to use your own model and run it in standalone mode, you will have to place its source code in ~/.simulation-gazebo.

You can fetch the script locally using any method you like, such as wget:

wget https://raw.githubusercontent.com/PX4/PX4-gazebo-models/main/simulation-gazebo

The script can be started with:

cd /path/to/script/
python3 simulation-gazebo

For more information and arguments, see Gazebo Models.

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.

# 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
baylands make px4_sitl *_baylands Baylands world surrounded by water

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.

Note

Baylands throws the following error, which can be ignored:

[Err] [SDFFeatures.cc:843] The geometry element of collision [collision] couldn't be created

This occurs because Baylands has a lot of meshes. However it does not break Gazebo and the error has been downgraded to a warning in Gazebo Harmonic: gz-physics/pull/531 (opens new window). You can also replace the error with a warning by installing gz-garden from source (opens new window).

# 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_SIM_MODEL.
  • PX4_SIM_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

    The environmental variable PX4_GZ_MODEL has been deprecated and its functionality merged into PX4_SIM_MODEL.

  • PX4_GZ_MODEL_POSE: Sets the spawning position and orientation of the model when PX4_SIM_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_SIM_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 Gazebo must be gz.

  • PX4_GZ_STANDALONE: Lets PX4 know that it should not launch an instance of Gazebo. Gazebo will need to be launched separately, as described in Standalone Mode.

The PX4 Gazebo worlds and and models databases can be found on Github here (opens new window).

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_SIM_MODEL=gz_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
    
  4. Start simulator in standalone mode + connect to Gazebo instance running default world

    PX4_GZ_STANDALONE=1 PX4_SYS_AUTOSTART=4001 PX4_SIM_MODEL=gz_x500 ./build/px4_sitl_default/bin/px4
    

    In a separate terminal run:

    python /path/to/simulation-gazebo
    

# Adding New Worlds and Models

SDF files, mesh files, textures and anything else to do with the functionality and appearance in Gazebo for worlds and models can be placed in the appropriate /worlds and /models directories in PX4-gazebo-models (opens new window).

Within PX4 follow the below steps to add models and worlds.

# Adding a Model

To add a new model:

  1. Define an airframe configuration file.

  2. 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
      
  3. Add CMake Target for the airframe (opens new window).

    • If you plan to use "regular" mode, add your model SDF to Tools/simulation/gz/models/.
    • If you plan to use standalone mode, add your model SDF to ~/.simulation-gazebo/models/

    You can of course also use both.

# Adding a World

To add a new world:

  1. Add your world to the list of worlds found in the CMakeLists.txt here (opens new window). This is required in order to allow CMake to generate correct targets.

    • If you plan to use "normal" mode, add your world sdf to Tools/simulation/gz/worlds/.
    • If you plan to use standalone mode, add your world SDF to ~/.simulation-gazebo/worlds/

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