airsim_ros_pkgs#

A ROS wrapper over the AirSim C++ client library.

Setup#

  • Install gcc >= 8.0.0: sudo apt-get install gcc-8 g++-8
    Verify installation by gcc-8 --version

  • Ubuntu 16.04

    • Install ROS kinetic
    • Install tf2 sensor and mavros packages: sudo apt-get install ros-kinetic-tf2-sensor-msgs ros-kinetic-tf2-geometry-msgs ros-kinetic-mavros*
  • Ubuntu 18.04

    • Install ROS melodic
    • Install tf2 sensor and mavros packages: sudo apt-get install ros-melodic-tf2-sensor-msgs ros-melodic-tf2-geometry-msgs ros-melodic-mavros*
  • Install catkin_tools sudo apt-get install python-catkin-tools or pip install catkin_tools

Build#

  • Build AirSim
    git clone https://github.com/Microsoft/AirSim.git;
    cd AirSim;
    ./setup.sh;
    ./build.sh;
  • Build ROS package
cd ros;
catkin build; # or catkin_make

If your default GCC isn't 8 or greater (check using gcc --version), then compilation will fail. In that case, use gcc-8 explicitly as follows-

catkin build -DCMAKE_C_COMPILER=gcc-8 -DCMAKE_CXX_COMPILER=g++-8

Running#

source devel/setup.bash;
roslaunch airsim_ros_pkgs airsim_node.launch;
roslaunch airsim_ros_pkgs rviz.launch;
Note: If you get an error running roslaunch airsim_ros_pkgs airsim_node.launch, run catkin clean and try again

Using AirSim ROS wrapper#

The ROS wrapper is composed of two ROS nodes - the first is a wrapper over AirSim's multirotor C++ client library, and the second is a simple PD position controller.
Let's look at the ROS API for both nodes:

AirSim ROS Wrapper Node#

Publishers:#

  • /airsim_node/origin_geo_point airsim_ros_pkgs/GPSYaw
    GPS coordinates corresponding to global NED frame. This is set in the airsim's settings.json file under the OriginGeopoint key.

  • /airsim_node/VEHICLE_NAME/global_gps sensor_msgs/NavSatFix
    This the current GPS coordinates of the drone in airsim.

  • /airsim_node/VEHICLE_NAME/odom_local_ned nav_msgs/Odometry
    Odometry in NED frame (default name: odom_local_ned, launch name and frame type are configurable) wrt take-off point.

  • /airsim_node/VEHICLE_NAME/CAMERA_NAME/IMAGE_TYPE/camera_info sensor_msgs/CameraInfo

  • /airsim_node/VEHICLE_NAME/CAMERA_NAME/IMAGE_TYPE sensor_msgs/Image
    RGB or float image depending on image type requested in settings.json.

  • /tf tf2_msgs/TFMessage

  • /airsim_node/VEHICLE_NAME/altimeter/SENSOR_NAME airsim_ros_pkgs/Altimeter
    This the current altimeter reading for altitude, pressure, and QNH

  • /airsim_node/VEHICLE_NAME/imu/SENSOR_NAME sensor_msgs::Imu
    IMU sensor data

  • /airsim_node/VEHICLE_NAME/magnetometer/SENSOR_NAME sensor_msgs::MagneticField
    Meausrement of magnetic field vector/compass

  • /airsim_node/VEHICLE_NAME/distance/SENSOR_NAME sensor_msgs::Range
    Meausrement of distance from an active ranger, such as infrared or IR

  • /airsim_node/VEHICLE_NAME/lidar/SENSOR_NAME sensor_msgs::PointCloud2
    LIDAR pointcloud

Subscribers:#

Services:#

Parameters:#

  • /airsim_node/world_frame_id [string]
    Set in: $(airsim_ros_pkgs)/launch/airsim_node.launch
    Default: world_ned
    Set to "world_enu" to switch to ENU frames automatically

  • /airsim_node/odom_frame_id [string]
    Set in: $(airsim_ros_pkgs)/launch/airsim_node.launch
    Default: odom_local_ned
    If you set world_frame_id to "world_enu", the default odom name will instead default to "odom_local_enu"

  • /airsim_node/coordinate_system_enu [boolean]
    Set in: $(airsim_ros_pkgs)/launch/airsim_node.launch
    Default: false
    If you set world_frame_id to "world_enu", this setting will instead default to true

  • /airsim_node/update_airsim_control_every_n_sec [double]
    Set in: $(airsim_ros_pkgs)/launch/airsim_node.launch
    Default: 0.01 seconds.
    Timer callback frequency for updating drone odom and state from airsim, and sending in control commands.
    The current RPClib interface to unreal engine maxes out at 50 Hz.
    Timer callbacks in ROS run at maximum rate possible, so it's best to not touch this parameter.

  • /airsim_node/update_airsim_img_response_every_n_sec [double]
    Set in: $(airsim_ros_pkgs)/launch/airsim_node.launch
    Default: 0.01 seconds.
    Timer callback frequency for receiving images from all cameras in airsim.
    The speed will depend on number of images requested and their resolution.
    Timer callbacks in ROS run at maximum rate possible, so it's best to not touch this parameter.

  • /airsim_node/publish_clock [double]
    Set in: $(airsim_ros_pkgs)/launch/airsim_node.launch
    Default: false
    Will publish the ros /clock topic if set to true.

Simple PID Position Controller Node#

Parameters:#

  • PD controller parameters:
  • /pd_position_node/kd_x [double],
    /pd_position_node/kp_y [double],
    /pd_position_node/kp_z [double],
    /pd_position_node/kp_yaw [double]
    Proportional gains

  • /pd_position_node/kd_x [double],
    /pd_position_node/kd_y [double],
    /pd_position_node/kd_z [double],
    /pd_position_node/kd_yaw [double]
    Derivative gains

  • /pd_position_node/reached_thresh_xyz [double]
    Threshold euler distance (meters) from current position to setpoint position

  • /pd_position_node/reached_yaw_degrees [double]
    Threshold yaw distance (degrees) from current position to setpoint position

  • /pd_position_node/update_control_every_n_sec [double]
    Default: 0.01 seconds

Services:#

  • /airsim_node/VEHICLE_NAME/gps_goal [Request: srv/SetGPSPosition]
    Target gps position + yaw.
    In absolute altitude.

  • /airsim_node/VEHICLE_NAME/local_position_goal [Request: srv/SetLocalPosition]
    Target local position + yaw in global NED frame.

Subscribers:#

  • /airsim_node/origin_geo_point airsim_ros_pkgs/GPSYaw
    Listens to home geo coordinates published by airsim_node.

  • /airsim_node/VEHICLE_NAME/odom_local_ned nav_msgs/Odometry
    Listens to odometry published by airsim_node

Publishers:#

Global params#

  • Dynamic constraints. These can be changed in dynamic_constraints.launch:

    • /max_vel_horz_abs [double]
      Maximum horizontal velocity of the drone (meters/second)

    • /max_vel_vert_abs [double]
      Maximum vertical velocity of the drone (meters/second)

    • /max_yaw_rate_degree [double]
      Maximum yaw rate (degrees/second)

Misc#

Setting up the Build Environment on Windows10 using WSL1 or WSL2#

These setup instructions describe how to setup "Bash on Ubuntu on Windows" (aka "Windows Subsystem for Linux").

It involves enabling the built-in Windows Linux environment (WSL) in Windows10, installing a compatible Linux OS image, and finally installing the build environment as if it were a normal Linux system.

Upon completion, you will be able to build and run the ros wrapper as in a native linux machine.

WSL1 vs WSL2#

WSL2 is the latest version of the Windows10 Subsystem for Linux. It is many times faster than WSL1 and is therefore much preferred for building the code in terms of speed.

Once installed, you can switch between WSL1 or WSL2 versions as you prefer.

WSL Setup steps#
  1. Follow the instructions here. Check that the ROS version you want to use is supported by the Ubuntu version you want to install.

  2. Congratulations, you now have a working Ubuntu subsystem under Windows, you can now go to Ubuntu 16 / 18 instructions and then How to run Airsim on Windows and ROS wrapper on WSL!

Note

You can run XWindows applications (including SITL) by installing VcXsrv on Windows. To use it find and run XLaunch from the Windows start menu.
Select Multiple Windows in first popup, Start no client in second popup, only Clipboard in third popup. Do not select Native Opengl (and if you are not able to connect select Disable access control).
You will need to set the DISPLAY variable to point to your display: in WSL it is 127.0.0.1:0, in WSL2 it will be the ip address of the PC's network port and can be set by using the code below. Also in WSL2 you may have to disable the firewall for public networks, or create an exception in order for VcXsrv to communicate with WSL2:

export DISPLAY=$(cat /etc/resolv.conf | grep nameserver | awk '{print $2}'):0

Tip

  • If you add this line to your ~/.bashrc file you won't need to run this command again
  • For code editing you can install VSCode inside WSL.
  • Windows 10 includes "Windows Defender" virus scanner. It will slow down WSL quite a bit. Disabling it greatly improves disk performance but increases your risk to viruses so disable at your own risk. Here is one of many resources/videos that show you how to disable it: How to Disable or Enable Windows Defender on Windows 10
File System Access between WSL and Windows10#

From within WSL, the Windows drives are referenced in the /mnt directory. For example, in order to list documents within your () documents folder:

`ls /mnt/c/'Documents and Settings'/<username>/Documents`
or
`ls /mnt/c/Users/<username>/Documents`

From within Windows, the WSL distribution's files are located at (type in windows Explorer address bar):

\\wsl$\<distribution name> e.g. \\wsl$\Ubuntu-18.04

How to run Airsim on Windows and ROS wrapper on WSL#

You need to have the same setting.json content for the simulator and WSL (e.g., in each Documents\Airsim folder). For WSL 1 execute:
export WSL_HOST_IP=127.0.0.1
and for WSL 2:
export WSL_HOST_IP=$(cat /etc/resolv.conf | grep nameserver | awk '{print $2}')
Now, as in the running section for linux, execute the following:

source devel/setup.bash
roslaunch airsim_ros_pkgs airsim_node.launch output:=screen host:=$WSL_HOST_IP
roslaunch airsim_ros_pkgs rviz.launch