FSDS ROS bridge

In action

A ROS wrapper over the AirSim C++ Car client library. This code is based on the original AirSim ROS wrapper for the Multirotor API and provides an interface between AirSim + Unreal Engine and your ROS-based autonomous system.

The fsds_ros_bridge is supposed to be launched pointing at the Autonomous System's ROS master so that it can publish and subscribe to topics within the autonomous system. Physically this node should run on the airsim simulation server (that is the one that also runs the Unreal) project. The node connects to the AirSim plugin, periodically retrieves sensor data (images, lidar, imu, gps) and publishes it on ROS topics. It listens for car setpoints on other another and forwards these to the AirSim plugin.

Nodes

The fsds_ros_bridge.launch launches the following nodes: * /fsds/ros_bridge node responsible for IMU, GPS, lidar, vehicle setpoints and go/finish signals. * /fsds/camera/CAMERANAME node is run for each camera configured in the settings.json. The nodes are launched using the cameralauncher.py script.

Published topics

Topic name	Description	Message	Rate (hz)
`/fsds/gps`	This the current GPS coordinates of the drone in airsim. Read all about the gps simulation model here. Data is in the `fsds/FSCar` frame.	sensor_msgs/NavSatFix	10
`/fsds/imu`	Velocity, orientation and acceleration information. Read all about the IMU model here. Data is in the `fsds/FSCar` (enu) frame.	sensor_msgs/Imu	250
`/fsds/gss`	Ground speed sensor provide linear velocity of the vehicle (`fsds/FSCar`). Velocity is m/s.	geometry_msgs/TwistWithCovarianceStamped	100
`/fsds/testing_only/odom`	Ground truth car position and orientation in ENU frame about the CoG of the car (`fsds/FSCar`). The units are `m` for distance. The orientation are expressed in terms of quaternions. The message is in the `fsds/map` frame. This is a frame that is not (yet) used anywhere else and is just here so you can easely reference it if needed.	nav_msgs/Odometry	250
`/fsds/testing_only/track`	Ground truth cone position and color with respect to the starting location of the car in ENU. Currently this only publishes the initial position of cones that are part of the track spline. Any cones placed manually in the world are not published here. Additionally, the track is published once and the message is latched (meaning it is always available for a newly created subscriber).	fs_msgs/Track	Latched
`/fsds/testing_only/extra_info`	This topic contains extra information about the simulator. At the moment these are the doo_counter, that keeps track of the amount of cones that have been hit, and the times of the laps	fs_msgs/ExtraInfo	1
`/fsds/camera/CAMERA_NAME`	Camera images. See ./camera.md.	sensor_msgs/Image	~18
`/fsds/lidar/LIDARNAME`	Publishes the lidar points for each lidar sensor. All points are in the `fsds/LIDARNAME` frame. Transformations between the `fsds/LIDARNAME` and `fsds/FSCar` frame are being published regularly. More info on the lidar sensor can be found here	sensor_msgs/PointCloud	`RotationsPerSecond param in `settings.json`
`/fsds/signal/go`	GO signal that is sent every second by the ROS bridge.The car is only allowed to drive once this message has been received. If no GO signal is received for more than 4 seconds, the AS can assume that `fsds_ros_bridge` has been shut down. This message also includes the mission type and track. More info about signal topics can be found in the competition-signals guide	fs_msgs/GoSignal	1
`/tf_static`	See Coordinate frames and transforms	tf2_msgs/TFMessage	1

Subscribed topics

Topic name	Description	Message
`/fsds/control_command`	This message includes the dimensionless values throttle, steering and brake. Throttle and brake range from 0 to 1. For steering `-1` steers full to the left and `+1` steers full to the right. Maximum steering angle is by default 25 degrees. The contents of this message fill the essential parts of the `msr::airlib::CarApiBase::CarControl` struct. This is the only way to control the car when the airsim ROS client is connected (keyboard will no longer work!).	fs_msgs/ControlCommand
`/fsds/signal/finished`	Finished signal that is sent by the AS to stop the mission. The ROS bridge will forward the signal to the operator which in turn will stop the ROS bridge and finish the run.	fs_msgs/FinishedSignal

Services

/fsds/reset fs_msgs/Reset
Resets car to start location.

Units

If a topic streams a standard ROS message (like sensor_msgs/Imu) then the units will be the recommended units in the message documentation. Custom messages (from the fs_msgs package) use the units specified in the message documentation as well. If in doubt, interpret distances in meters, angles in radians and rates in m/s and rad/s, etc.

Coordinate frames and transforms

The primary frame is the fsds/FSCar frame, which is fixed at the center of the car following the ROS coordinate system convention. The center of the car is the Unreal Engine car pawn position, which in turn is also the center of gravity.

The ROS bridge regularly publishes static transforms between the fsds/FSCar frame and each of the cameras and lidars. Naming of these frames is fsds/SENSORNAME. For example, a lidar named Example will publish it's points in the fsds/Example frame. The position and orientation of a camera named Test will become available in the frame /fsds/Test.

The transforms published on the /tf_static topic are the transforms specified in the settings.json.

Only static transforms within the vehicle are published.

All positions and rotations published by the ROS bridge are in line with the ROS defaults. This is the same coordinate system as everything else within the simulator.

Parameters

/fsds/ros_bridge/update_gps_every_n_sec [double]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch
Default: 0.1 seconds (10hz).
Timer callback frequency for updating and publishing the gps sensordata. This value must be equal or higher to the update frequency of the sensor configured in the settings.json
/fsds/ros_bridge/update_imu_every_n_sec [double]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch
Default: 0.004 seconds (250hz).
Timer callback frequency for updating and publishing the imu messages.
This value must be equal or higher to the minimual sample rate of the sensor configured in the settings.json
/fsds/ros_bridge/update_gss_every_n_sec [double]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch
Default: 0.01 seconds (100hz).
Timer callback frequency for updating and publishing the ground speed sensor messages.
/fsds/ros_bridge/update_odom_every_n_sec [double]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch
Default: 0.004 seconds (250hz).
Timer callback frequency for updating and publishing the odometry.
/fsds/ros_bridge/publish_static_tf_every_n_sec [double]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch
Default: 1 seconds (1 hz).
The frequency at which the static transforms are published.
/fsds/ros_bridge/update_lidar_every_n_sec [double]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch
Default: 0.1 seconds (10 hz).
The frequency at which the lidar is publshed.
/fsds/ros_bridge/competition_mode [bool]
Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch Default: false, during competition set to true If competition mode is enabled, the testing_only topics won't be available.
/fsds/ros_bridge/manual_mode [bool] Set in: $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch Default: false Do not enable vehicle api control. You can control the car using the keyboard in the simulator.
/fsds/ros_bridge/UDP_control [bool] Set in $(fsds_ros_bridge)/launch/fsds_ros_bridge.launch Default: false Force UDP connection for the fsds/controlCommand topic when running the fsds_ros_bridge in WSL

Visualization

This package contains some useful launch and config files which will help you in visualizing the data being streamed through the above topics.

To open Rviz with this configuration file, run roslaunch fsds_ros_bridge fsds_ros_bridge.launch rviz:=true.

To open Multiplot with this configuration file, run roslaunch fsds_ros_bridge fsds_ros_bridge.launch plot:=true.

Monitoring

Performance monitoring of the ROS Bridge is described here