Aerostack2 Gazebo ROS Bridge
Gazebo defines it’s own messages in a ROS 2 decoupled communication protocol, for instance, in order to get this data to work in ROS 2 network, we need to use a intermediate bridge that publish this data into ROS 2.
Library ros_gz_bridge provides a network bridge which enables the exchange of messages between ROS 2 and Gazebo Transport. Messages in Gazebo Transport are published by plugins. As Gazebo’s architecture is based on an Entity Component System (ECS), plugins provides the functionality for each component, like sensors. Its support is limited to only certain message types. Aerostack2 uses this component’s functionality to provide message conversion. The gz messages regarding the robot model that are passed to ROS 2 are included in the following table:
Gz Topic |
ROS Topic |
Gz message type |
ROS message type |
|---|---|---|---|
/clock |
/clock |
ignition.msgs.Clock |
rosgraph_msgs/msg/Clock |
/model/{model_name}/odometry |
{namespace}/ground_truth/pose |
ignition.msgs.Odometry |
geometry_msgs/msg/PoseStamped |
/model/{model_name}/odometry |
{namespace}/ground_truth/speed |
ignition.msgs.Odometry |
geometry_msgs/msg/TwistStamped |
To communicate ROS 2 commands with Gazebo, ros_gz_bridge can work the other way around, translating messages from ROS 2 to Gazebo so we can arm the aerial robot and send speed commands from the controller. This is a unique characteristic of this platform as it is only simulated, ROS 2 communication tools are used to send speed commands:
Gz Topic |
ROS Topic |
Gz message type |
ROS message type |
|---|---|---|---|
/model/{model_name}/velocity_controller/enable |
/gz/{model_name}/arm |
ignition.msgs.Boolean |
std_msgs/msg/Bool |
/model/{model_name}/cmd_vel |
/gz/{model_name}/cmd_vel |
ignition.msgs.Twist |
geometry_msgs/msg/Twist |
Sensors
Aerostack2 is provided with different types of sensors from Gazebo sensor library. These sensors can be attached to models in order to simulate the physical model of the sensor in the world and its functionality. To get the information coming from these sensor’s Gazebo plugins, Aerostack2 brings these messages to ROS 2 like the following table indicates:
Sensor |
Gz Topic |
ROS Topic |
Gz message type |
ROS message type |
|---|---|---|---|---|
IMU |
{sensor_prefix}/imu/imu |
{namespace}/sensor_measurements/imu |
ignition.msgs.IMU |
sensor_msgs/msg/Imu |
Magnetometer |
{sensor_prefix}/magnetometer/magnetometer |
{namespace}/sensor_measurements/magnetic_field |
ignition.msgs.Magnetometer |
sensor_msgs/msg/MagneticField |
Air pressure |
{sensor_prefix}/air_pressure/air_pressure |
{namespace}/sensor_measurements/air_pressure |
ignition.msgs.FluidPressure |
sensor_msgs/msg/FluidPressure |
Battery |
/model/{model_name}/battery/linear_battery/state |
{namespace}/sensor_measurements/battery |
ignition.msgs.BatteryState |
sensor_msgs/msg/BatteryState |
Camera |
{sensor_prefix}/camera/image |
{namespace}/sensor_measurements/{model_prefix}/image_raw |
ignition.msgs.Image |
sensor_msgs/msg/Image |
Depth camera |
{sensor_prefix}/camera/depth_image |
{namespace}/sensor_measurements/{model_prefix}/depth |
ignition.msgs.Image |
sensor_msgs/msg/Image |
Camera |
{sensor_prefix}/camera/camera_info |
{namespace}/sensor_measurements/{model_prefix}/camera_info |
ignition.msgs.CameraInfo |
sensor_msgs/msg/CameraInfo |
Lidar |
{sensor_prefix}/gpu_ray/scan |
{namespace}/sensor_measurements/{model_prefix}/scan |
ignition.msgs.LaserScan |
sensor_msgs/msg/LaserScan |
Lidar |
{sensor_prefix}/gpu_ray/scan/points |
{namespace}/sensor_measurements/{model_prefix}/points |
ignition.msgs.PointCloudPacked |
sensor_msgs/msg/PointCloud2 |
Camera |
{sensor_prefix}/camera/points |
{namespace}/sensor_measurements/{model_prefix}/points |
ignition.msgs.PointCloudPacked |
sensor_msgs/msg/PointCloud2 |