Gazebo 仿真

Gazebo 是用于自主机器人的强大3D模拟环境,其特别适用于测试物体避障和计算机视觉。 本文描述了如何使用它来进行单机的软件在环仿真。 Gazebo 也可以适用于 硬件在环仿真多机仿真

Supported Vehicles: Quad (Iris and Solo, Hex (Typhoon H480), Generic quad delta VTOL, Tailsitter, Plane, Rover, Submarine/UUV.

Gazebo is often used with ROS, a toolkit/offboard API for automating vehicle control. If you plan to use PX4 with ROS you should follow the ROS Instructions to install both ROS and Gazebo (and thereby avoid installation conflicts).

GazeboPluginMAVLinkSITL

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

Installation

Gazebo 9 的安装在标准的环境编译已有说明。

其他安装说明可在 gazebosim.org 上找到。

运行仿真

Run a simulation by starting PX4 SITL and gazebo 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 Firmware repository and call make for the desired target. For example, to start a quadrotor simulation (the default):

cd /path/to/Firmware
make px4_sitl gazebo

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

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

Vehicle Command
Quadrotor make px4_sitl gazebo
Quadrotor with Optical Flow make px4_sitl gazebo_iris_opt_flow
3DR Solo (Quadrotor) make px4_sitl gazebo_solo
Typhoon H480 (Hexrotor) (supports video streaming) make px4_sitl gazebo_typhoon_h480
Standard Plane make px4_sitl gazebo_plane
Standard VTOL make px4_sitl gazebo_standard_vtol
Tailsitter VTOL make px4_sitl gazebo_tailsitter
Ackerman vehicle (UGV/Rover) make px4_sitl gazebo_rover
HippoCampus TUHH (UUV: Unmanned Underwater Vehicle) make px4_sitl gazebo_uuv_hippocampus
Boat (USV: Unmanned Surface Vehicle) make px4_sitl gazebo_boat

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 running and only re-launch PX4 when needed (quicker than restarting both).
  • Run the simulation in Headless Mode, which does not start the Gazebo 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 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.

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

Gazebo UI

You can bring it into the air by typing:

pxh> commander takeoff

Usage/Configuration Options

Headless Mode

Gazebo can be run in a headless mode in which the Gazebo 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_plane

Set Custom Takeoff Location

The default takeoff location in SITL Gazebo can be overridden using environment variables.

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

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

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

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/sitl_gazebo/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 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. 构建任何 gazebo 目标以生成 SDF 文件(适用于所有机型)。 例如: make px4_sitl gazebo_iris >Tip在后续版本中不会覆盖 SDF 文件。
  2. 打开目标车辆的 SDF 文件(例如./Tools/sitl_gazebo/models/iris/iris.sdf )。
  3. 搜索 gpsNoise 元素:

     xml
     <plugin name='gps_plugin' filename='libgazebo_gps_plugin.so'>
      <robotNamespace/>
      <gpsNoise>true</gpsNoise>
     </plugin>
    
    • 如果存在,则启用 GPS。 您可以通过删除以下行来禁用它:<gpsNoise> true </gpsNoise>
    • 如果未预设,则禁用 GPS 。 您可以通过将gpsNoise元素添加到gps_plugin部分来启用它(如上所示)。

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

Loading a Specific World

PX4 supports a number of Gazebo Worlds, which are stored in PX4/sitl_gazebo/worlds) By default Gazebo 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_plane_cam__warehouse

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.

Starting Gazebo and PX4 Separately

For extended development sessions it might be more convenient to start Gazebo 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 and PX4 separately:

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

      sh
      make px4_sitl gazebo___ide or 
    
      sh
      make px4_sitl gazebo_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 (e.g. Gazebo) is always running in background and you only re-run the px4 process which is very light.

Simulated Survey Camera

The Gazebo 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: Firmware/build/px4sitle_default/tmp/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_plane_cam

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.

The simulated camera is implemented in PX4/sitl_gazebo/src/gazebo_geotagged_images_plugin.cpp.

Simulated Parachute/Flight Termination

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

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

make px4_sitl gazebo_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:

Video Streaming

PX4 SITL for Gazebo supports UDP video streaming from a Gazebo camera sensor attached to a vehicle model. When streaming is enabled, you can connect to this stream from QGroundControl (on UDP port 5600) and view video of the Gazebo 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 UI.

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

Prerequisites

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

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_typhoon_h480

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

Video ON/OFF button

How to View Gazebo Video

The easiest way to view the SITL/Gazebo 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:

QGC Video Streaming Settings for Gazebo

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

QGC Video Streaming Gazebo Example

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

Extending and Customizing

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

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

Further Information

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