Gazebo Classic Simulation

WARNING

Gazebo Classic is supported with PX4 up to Ubuntu Linux 20.04. In Ubuntu 22.04 and later you must use Gazebo (which was formerly known as "Gazebo Ignition").

Gazebo Classic is a powerful 3D simulation environment for autonomous robots that is particularly suitable for testing object-avoidance and computer vision. This page describes its use with SITL and a single vehicle. Gazebo Classic can also be used with HITL and for multi-vehicle simulation.

Supported Vehicles: Quad (Iris, Hex (Typhoon H480), Generic Standard VTOL (QuadPlane), Tailsitter, Plane, Rover, Submarine/UUV.

INFO

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

Installation

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If you plan to use PX4 with ROS you should follow the ROS Instructions to install both ROS and Gazebo Classic (and thereby avoid installation conflicts).

Gazebo Classic setup is included in our standard build instructions for macOS, Ubuntu 18.04 and 20.04, and Windows on WSL2 for the same hosts.

For Ubuntu 22.04 LTS and later, the installation script (/Tools/setup/ubuntu.sh) installs the Gazebo simulator instead.

If you want to use Gazebo Classic on Ubuntu 22.04 you can use the following commands to remove Gazebo (Harmonic) and then reinstall Gazebo-Classic 11:

sudo apt remove gz-harmonic
sudo apt install aptitude
sudo aptitude install gazebo libgazebo11 libgazebo-dev

Note that aptitude is needed because it can resolve dependency conflicts (by removing certain packages) that apt is unable to handle.

TIP

You could also modify the installation script to install Gazebo Classic on later versions before it is run for the first time.

Additional installation instructions can be found on gazebosim.org.

Running the Simulation

Run a simulation by starting PX4 SITL and Gazebo Classic with the airframe configuration to load (multicopters, planes, VTOL, optical flow and multi-vehicle simulations are supported).

The easiest way to do this is to open a terminal in the root directory of the PX4 PX4-Autopilot repository and call make for the desired target. For example, to start a quadrotor simulation (the default):

cd /path/to/PX4-Autopilot
make px4_sitl gazebo-classic

The supported vehicles and make commands are listed below (click links to see vehicle images).

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For the full list of build targets run make px4_sitl list_vmd_make_targets (and filter on those that start with gazebo-classic_).

Vehicle	Command
Quadrotor	make px4_sitl gazebo-classic
Quadrotor with Optical Flow	make px4_sitl gazebo-classic_iris_opt_flow
Quadrotor with Depth Camera (forward-facing)	make px4_sitl gazebo-classic_iris_depth_camera
Quadrotor with Depth Camera (downward-facing)	make px4_sitl gazebo-classic_iris_downward_depth_camera
3DR Solo (Quadrotor)	make px4_sitl gazebo-classic_solo
Typhoon H480 (Hexrotor) (with video streaming)	make px4_sitl gazebo-classic_typhoon_h480
Standard Plane	make px4_sitl gazebo-classic_plane
Standard Plane (with catapult launch)	make px4_sitl gazebo-classic_plane_catapult
Standard VTOL	make px4_sitl gazebo-classic_standard_vtol
Tailsitter VTOL	make px4_sitl gazebo-classic_tailsitter
Ackerman UGV (Rover)	make px4_sitl gazebo-classic_rover
Differential UGV (Rover)	make px4_sitl gazebo-classic_r1_rover
HippoCampus TUHH (UUV: Unmanned Underwater Vehicle)	make px4_sitl gazebo-classic_uuv_hippocampus
Boat (USV: Unmanned Surface Vehicle)	make px4_sitl gazebo-classic_boat
Cloudship (Airship)	make px4_sitl gazebo-classic_cloudship

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The Installing Files and Code guide is a useful reference if there are build errors.

The commands above launch a single vehicle with the full UI. Other options include:

• Starting PX4 and Gazebo separately so that you can keep Gazebo Classic running and only re-launch PX4 when needed (quicker than restarting both).
• Run the simulation in Headless Mode, which does not start the Gazebo Classic UI (this uses fewer resources and is much faster).

Taking it to the Sky

The make commands above first build PX4, and then run it along with the Gazebo Classic simulator.

Once PX4 has started it will launch the PX4 shell as shown below.

______  __   __    ___
| ___ \ \ \ / /   /   |
| |_/ /  \ V /   / /| |
|  __/   /   \  / /_| |
| |     / /^\ \ \___  |
\_|     \/   \/     |_/

px4 starting.

INFO  [px4] Calling startup script: /bin/sh etc/init.d-posix/rcS 0
INFO  [param] selected parameter default file eeprom/parameters_10016
[param] Loaded: eeprom/parameters_10016
INFO  [dataman] Unknown restart, data manager file './dataman' size is 11798680 bytes
INFO  [simulator] Waiting for simulator to connect on TCP port 4560
Gazebo multi-robot simulator, version 9.0.0
Copyright (C) 2012 Open Source Robotics Foundation.
Released under the Apache 2 License.
http://gazebosim.org
...
INFO  [ecl/EKF] 5188000: commencing GPS fusion

The console will print out status as PX4 loads the airframe-specific initialisation and parameter files, waits for (and connects to) the simulator. Once there is an INFO print that [ecl/EKF] is commencing GPS fusion the vehicle is ready to arm.

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Right-clicking the quadrotor model allows to enable follow mode from the context menu, which is handy to keep it in view.

You can bring it into the air by typing:

pxh> commander takeoff

Usage/Configuration Options

Options that apply to all simulators are covered in the top level Simulation topic (some of these may be duplicated below).

Simulating Sensor/Hardware Failure

Simulate Failsafes explains how to trigger safety failsafes like GPS failure and battery drain.

Headless Mode

Gazebo Classic can be run in a headless mode in which the Gazebo Classic UI is not launched. This starts up more quickly and uses less system resources (i.e. it is a more "lightweight" way to run the simulation).

Simply prefix the normal make command with HEADLESS=1 as shown:

HEADLESS=1 make px4_sitl gazebo-classic_plane

Set Custom Takeoff Location

The takeoff location in Gazebo Classic can be set using environment variables. This will override both the default takeoff location, and any value set for the world.

The variables to set are: PX4_HOME_LAT, PX4_HOME_LON, and PX4_HOME_ALT.

For example:

export PX4_HOME_LAT=28.452386
export PX4_HOME_LON=-13.867138
export PX4_HOME_ALT=28.5
make px4_sitl gazebo-classic

Change Simulation Speed

The simulation speed can be increased or decreased with respect to realtime using the environment variable PX4_SIM_SPEED_FACTOR.

export PX4_SIM_SPEED_FACTOR=2
make px4_sitl_default gazebo-classic

For more information see: Simulation > Run Simulation Faster than Realtime.

Change Wind Speed

To simulate wind speed, add this plugin to your world file and set windVelocityMean in m/s (replace SET_YOUR_WIND_SPEED with your desired speed). If needed, adapt the windVelocityMax parameter so that it is greater than windVelocityMean:

  <plugin name='wind_plugin' filename='libgazebo_wind_plugin.so'>
      <frameId>base_link</frameId>
      <robotNamespace/>
      <windVelocityMean>SET_YOUR_WIND_SPEED</windVelocityMean>
      <windVelocityMax>20.0</windVelocityMax>
      <windVelocityVariance>0</windVelocityVariance>
      <windDirectionMean>0 1 0</windDirectionMean>
      <windDirectionVariance>0</windDirectionVariance>
      <windGustStart>0</windGustStart>
      <windGustDuration>0</windGustDuration>
      <windGustVelocityMean>0</windGustVelocityMean>
      <windGustVelocityMax>20.0</windGustVelocityMax>
      <windGustVelocityVariance>0</windGustVelocityVariance>
      <windGustDirectionMean>1 0 0</windGustDirectionMean>
      <windGustDirectionVariance>0</windGustDirectionVariance>
      <windPubTopic>world_wind</windPubTopic>
    </plugin>

Wind direction is passed as a direction vector (standard ENU convention), which will be normalized in the gazebo plugin. Additionally you can state wind velocity variance in (m/s)² and direction variance based on a normal distribution to add some random factor into the simulation. Gust is internally handled in the same way as wind, with the slight difference that you can state start time and duration with the following two parameters windGustStart and windGustDuration.

You can see how this is done in PX4/PX4-SITL_gazebo-classic/worlds/windy.world.

Using a Joystick

Joystick and thumb-joystick support are supported through QGroundControl (setup instructions here).

Improving Distance Sensor Performance

The current default world is PX4-Autopilot/Tools/simulation/gazebo-classic/sitl_gazebo-classic/worlds/iris.world), which uses a heightmap as ground.

This can cause difficulty when using a distance sensor. If there are unexpected results we recommend you change the model in iris.model from uneven_ground to asphalt_plane.

Simulating GPS Noise

Gazebo Classic can simulate GPS noise that is similar to that typically found in real systems (otherwise reported GPS values will be noise-free/perfect). This is useful when working on applications that might be impacted by GPS noise - e.g. precision positioning.

GPS noise is enabled if the target vehicle's SDF file contains a value for the gpsNoise element (i.e. it has the line: <gpsNoise>true</gpsNoise>). It is enabled by default in many vehicle SDF files: solo.sdf, iris.sdf, standard_vtol.sdf, delta_wing.sdf, plane.sdf, typhoon_h480, tailsitter.sdf.

To enable/disable GPS noise:

1. Build any gazebo target in order to generate SDF files (for all vehicles). For example:

   make px4_sitl gazebo-classic_iris

   TIP

   The SDF files are not overwritten on subsequent builds.

2. Open the SDF file for your target vehicle (e.g. ./Tools/simulation/gazebo-classic/sitl_gazebo-classic/models/iris/iris.sdf).

3. Search for the gpsNoise element:

   <plugin name='gps_plugin' filename='libgazebo_gps_plugin.so'>
     <robotNamespace/>
     <gpsNoise>true</gpsNoise>
   </plugin>

   • If it is present, GPS is enabled. You can disable it by deleting the line: <gpsNoise>true</gpsNoise>
   • If it is not present, GPS is disabled. You can enable it by adding the gpsNoise element to the gps_plugin section (as shown above).

The next time you build/restart Gazebo Classic it will use the new GPS noise setting.

Loading a Specific World

PX4 supports a number of Worlds, which are stored in PX4-Autopilot/Tools/simulation/gazebo-classic/sitl_gazebo-classic/worlds. By default Gazebo Classic displays a flat featureless plane, as defined in empty.world.

You can load any of the worlds by specifying them as the final option in the PX4 configuration target.

For example, to load the warehouse world, you can append it as shown:

make px4_sitl_default gazebo-classic_plane_cam__warehouse

INFO

There are two underscores after the model (plane_cam) indicating that the default debugger is used (none). See Building the Code > PX4 Make Build Targets.

You can also specify the full path to a world to load using the PX4_SITL_WORLD environment variable. This is useful if testing a new world that is not yet included with PX4.

TIP

If the loaded world does not align with the map, you may need to set the world location.

Set World Location

The vehicle gets spawned very close to the origin of the world model at some simulated GPS location.

INFO

The vehicle is not spawned exactly at the Gazebo origin (0,0,0), but using a slight offset, which can highlight a number of common coding issues.

If using a world that recreates a real location (e.g. a particular airport) this can result in a very obvious mismatch between what is displayed in the simulated world, and what is shown on the ground station map. To overcome this problem you can set the location of the world origin to the GPS coordinates where it would be in "real life".

INFO

You can also set a Custom Takeoff Location that does the same thing. However adding the location to the map is easier (and can still be over-ridden by setting a custom location if needed).

The location of the world is defined in the .world file by specifying the location of the origin using the spherical_coordinates tag. The latitude, longitude, elevation must all be specified (for this to be a valid).

An example can be found in the sonoma_raceway.world:

    <spherical_coordinates>
      <surface_model>EARTH_WGS84</surface_model>
      <latitude_deg>38.161479</latitude_deg>
      <longitude_deg>-122.454630</longitude_deg>
      <elevation>488.0</elevation>
    </spherical_coordinates>

You can test this by spawning a rover in the Sonoma Raceway World using the following make command (note that spawning takes longer the first time as the model needs to be downloaded from the model database):

make px4_sitl gazebo-classic_rover__sonoma_raceway

The video below shows that the location of the environment is aligned with the world:

Starting Gazebo and PX4 Separately

For extended development sessions it might be more convenient to start Gazebo Classic and PX4 separately or even from within an IDE.

In addition to the existing cmake targets that run sitl_run.sh with parameters for px4 to load the correct model it creates a launcher targets named px4_<mode> that is a thin wrapper around original sitl px4 app. This thin wrapper simply embeds app arguments like current working directories and the path to the model file.

To start Gazebo Classic and PX4 separately:

• Run gazebo classic (or any other sim) server and client viewers via the terminal specifying an _ide variant:

  make px4_sitl gazebo-classic___ide

  or

  make px4_sitl gazebo-classic_iris_ide

• In your IDE select px4_<mode> target you want to debug (e.g. px4_iris)

• Start the debug session directly from IDE

This approach significantly reduces the debug cycle time because simulator is always running in background and you only re-run the px4 process which is very light.

Simulated Survey Camera

The Gazebo Classic survey camera simulates a MAVLink camera that captures geotagged JPEG images and sends camera capture information to a connected ground station. The camera also supports video streaming. It can be used to test camera capture, in particular within survey missions.

The camera emits the CAMERA_IMAGE_CAPTURED message every time an image is captured. The captured images are saved to: PX4-Autopilot/build/px4_sitl_default/src/modules/simulation/simulator_mavlink/frames/DSC_n.jpg (where n starts as 00000 and is iterated by one on each capture). To simulate a plane with this camera:

make px4_sitl_default gazebo-classic_plane_cam

INFO

The camera also supports/responds to the following MAVLink commands: MAV_CMD_REQUEST_CAMERA_CAPTURE_STATUS, MAV_CMD_REQUEST_STORAGE_INFORMATION, MAV_CMD_REQUEST_CAMERA_SETTINGS, MAV_CMD_REQUEST_CAMERA_INFORMATION, MAV_CMD_RESET_CAMERA_SETTINGS, MAV_CMD_STORAGE_FORMAT, MAV_CMD_SET_CAMERA_ZOOM, MAV_CMD_IMAGE_START_CAPTURE, MAV_CMD_IMAGE_STOP_CAPTURE, MAV_CMD_REQUEST_VIDEO_STREAM_INFORMATION, MAV_CMD_REQUEST_VIDEO_STREAM_STATUS, MAV_CMD_SET_CAMERA_MODE.

INFO

The simulated camera is implemented in PX4/PX4-SITL_gazebo-classic/main/src/gazebo_camera_manager_plugin.cpp.

Simulated Depth Camera

The Gazebo Classic depth camera model simulates an Intel® RealSense™ D455 stereo depth camera using the Openni Kinect plugin.

This publishes depth images and camera information on the /camera/depth/image_raw and /camera/depth/camera_info ROS topics respectively.

To use these images, you will need to install ROS or ROS 2. Note the warning at the top of this page about how to "avoid installation conflicts" when installing ROS and Gazebo.

You can simulate a quadrotor with a forward-facing depth camera:

make px4_sitl gazebo-classic_iris_depth_camera

or a quadrotor with a downward-facing depth camera:

make px4_sitl gazebo-classic_iris_downward_depth_camera

Simulated Parachute/Flight Termination

Gazebo Classic can be used to simulate deploying a parachute during Flight Termination (flight termination is triggered by the PWM command that is simulated in Gazebo Classic).

The if750a target has a parachute attached to the vehicle. To simulate the vehicle, run the following command:

make px4_sitl gazebo-classic_if750a

To put the vehicle into flight termination state, you can force it to fail a safety check that has flight termination set as the failsafe action. For example, you could do this by forcing a Geofence violation.

For more information see:

• Flight Termination
• Parachute
• Safety Configuration (Failsafes)

Video Streaming

PX4 SITL for Gazebo Classic supports UDP video streaming from a camera sensor attached to a simulated vehicle model. When streaming is enabled, you can connect to this stream from QGroundControl (on UDP port 5600) and view video of the Gazebo Classic environment from the simulated vehicle - just as you would from a real camera. The video is streamed using a gstreamer pipeline and can be enabled/disabled using a button in the Gazebo Classic UI.

The simulated camera sensor is supported/enabled on the following frames:

• Typhoon H480

Prerequisites

Gstreamer 1.0 is required for video streaming. The required dependencies should already have been installed when you set up Gazebo Classic (they are included in the standard PX4 installation scripts/instructions for macOS and Ubuntu Linux).

INFO

FYI only, the dependencies include: gstreamer1.0-plugins-base, gstreamer1.0-plugins-good, gstreamer1.0-plugins-bad, gstreamer1.0-plugins-ugly, libgstreamer-plugins-base1.0-dev.

Start/Stop Video Streaming

Video streaming is automatically started when supported by the target vehicle. For example, to start streaming video on the Typhoon H480:

make px4_sitl gazebo-classic_typhoon_h480

Streaming can be paused/restarted using the Gazebo UI Video ON/OFF button..

How to View Gazebo Video

The easiest way to view the SITL/Gazebo Classic camera video stream is in QGroundControl. Simply open Application Settings > General and set Video Source to UDP h.264 Video Stream and UDP Port to 5600:

The video from Gazebo Classic should then display in QGroundControl just as it would from a real camera.

INFO

The Typhoon world is not very interesting.

It is also possible to view the video using the Gstreamer Pipeline. Simply enter the following terminal command:

gst-launch-1.0  -v udpsrc port=5600 caps='application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)H264' \
! rtph264depay ! avdec_h264 ! videoconvert ! autovideosink fps-update-interval=1000 sync=false

Verbose Logging

SITL fails silently when there is something wrong with the model. You can enable more verbose logging using VERBOSE_SIM, as shown:

export VERBOSE_SIM=1
make px4_sitl gazebo-classic

or

VERBOSE_SIM=1 make px4_sitl gazebo-classic

Extending and Customizing

To extend or customize the simulation interface, edit the files in the Tools/simulation/gazebo/sitl_gazebo folder. The code is available on the sitl_gazebo repository on Github.

INFO

The build system enforces the correct GIT submodules, including the simulator. It will not overwrite changes in files in the directory.

Further Information

• ROS with Gazebo Classic Simulation
• Gazebo Classic Octomap