RDC_Simulation/docs/gazebo.md

Gazebo Simulation Guide

Running the GPS-denied drone simulation with Gazebo Ignition Fortress on Linux/WSL2.

Quick Start (Two Terminals)

Terminal 1 - Launch Gazebo + Bridge:

source activate.sh
ros2 launch gazebo/launch/drone_landing.launch.py

Terminal 2 - Run Controllers:

source activate.sh
python run_gazebo.py --pattern circular --speed 0.3

Both the drone AND rover will move!

Command Options

python run_gazebo.py --help

Options:
  --pattern       stationary, linear, circular, square, random
  --speed, -s     Rover speed in m/s (default: 0.5)
  --amplitude, -a Movement amplitude (default: 2.0)
  --no-rover      Disable rover controller

How It Works

1. Gazebo runs the physics simulation with:

   • Drone with VelocityControl plugin (responds to /drone/cmd_vel)
   • Rover with VelocityControl plugin (responds to /rover/cmd_vel)

2. ros_gz_bridge connects Gazebo topics to ROS 2

3. run_gazebo.py starts:

   • GazeboBridge - converts ROS topics to telemetry format
   • DroneController - your landing algorithm
   • RoverController - moves the landing pad

GPS-Denied Sensors

The GazeboBridge provides the same sensor interface as PyBullet:

Sensor	Source
IMU	Gazebo odometry orientation
Altimeter	Gazebo Z position
Velocity	Gazebo twist
Camera	Gazebo camera sensor (if enabled)
Landing Pad	Computed from relative position

Topics

ROS 2 Topics (your code uses these)

Topic	Type	Direction
/cmd_vel	Twist	Input (from DroneController)
/drone/telemetry	String	Output (to DroneController)
/rover/telemetry	String	Output (rover position)

Gazebo Topics (bridged automatically)

Topic	Type	Description
/drone/cmd_vel	Twist	Drone velocity commands
/rover/cmd_vel	Twist	Rover velocity commands
/model/drone/odometry	Odometry	Drone state
/drone/imu	IMU	IMU sensor data
/clock	Clock	Simulation time

Headless Mode (WSL2 / No GPU)

Run Gazebo without GUI:

# Server mode only
ign gazebo -s gazebo/worlds/drone_landing.sdf

Then run the bridge manually:

ros2 run ros_gz_bridge parameter_bridge \
  /drone/cmd_vel@geometry_msgs/msg/Twist]ignition.msgs.Twist \
  /rover/cmd_vel@geometry_msgs/msg/Twist]ignition.msgs.Twist \
  /model/drone/odometry@nav_msgs/msg/Odometry[ignition.msgs.Odometry

World File Details

The world file gazebo/worlds/drone_landing.sdf includes:

• Drone at (0, 0, 2) with:

  • VelocityControl plugin for movement
  • OdometryPublisher plugin for telemetry
  • IMU sensor

• Landing Pad (Rover) at (0, 0, 0.15) with:

  • VelocityControl plugin for movement
  • Visual H marker

Troubleshooting

Drone falls immediately

The drone should hover with the controller running. If it falls:

1. Check that run_gazebo.py is running
2. Verify the bridge shows "Passing message from ROS"
3. Check /drone/cmd_vel topic: ros2 topic echo /drone/cmd_vel

Rover doesn't move

1. Check that /rover/cmd_vel is bridged
2. Verify RoverController is publishing: ros2 topic echo /rover/cmd_vel

Model not found

Set the model path:

export GZ_SIM_RESOURCE_PATH=$PWD/gazebo/models:$GZ_SIM_RESOURCE_PATH
export IGN_GAZEBO_RESOURCE_PATH=$PWD/gazebo/models:$IGN_GAZEBO_RESOURCE_PATH

"Cannot connect to display" (WSL2)

Use headless mode:

ign gazebo -s gazebo/worlds/drone_landing.sdf

Or ensure WSLg is working:

export DISPLAY=:0

Plugin not found

For Ignition Fortress, plugins use libignition-gazebo-*-system.so naming.

Check available plugins:

ls /usr/lib/x86_64-linux-gnu/ign-gazebo-6/plugins/

Launch File Options

ros2 launch gazebo/launch/drone_landing.launch.py use_sim_time:=true

Argument	Default	Description
use_sim_time	true	Use Gazebo clock