RDC_Simulation/docs/gazebo.md

Gazebo Simulation

Running the GPS-denied drone simulation with Gazebo.

Prerequisites

Install Gazebo and ROS-Gazebo bridge:

./setup/install_ubuntu.sh
source activate.sh

Quick Start

Terminal 1 - Start Gazebo:

source activate.sh
gz sim gazebo/worlds/drone_landing.sdf

Terminal 2 - Spawn drone and start bridge:

source activate.sh

# Spawn drone
gz service -s /world/drone_landing_world/create \
  --reqtype gz.msgs.EntityFactory \
  --reptype gz.msgs.Boolean \
  --req 'sdf_filename: "gazebo/models/drone/model.sdf", name: "drone"'

# Start bridge
python gazebo_bridge.py

Terminal 3 - Run controllers:

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

World Description

The drone_landing.sdf world contains:

Object	Description
Ground Plane	Infinite flat surface
Sun	Directional light with shadows
Landing Pad	Green box with "H" marker at origin

Drone Model

Quadrotor drone with:

• Body: 0.3m × 0.3m × 0.1m, 1.0 kg
• Rotors: 4 spinning rotors
• IMU: Orientation and angular velocity
• Camera: 320x240 downward-facing sensor
• Odometry: Position and velocity

Gazebo Plugins

Plugin	Function
MulticopterMotorModel	Motor dynamics
MulticopterVelocityControl	Velocity commands
OdometryPublisher	Pose and twist

Camera System

The drone has a downward-facing camera:

Property	Value
Resolution	320 x 240
FOV	60 degrees
Format	Base64 encoded JPEG
Update Rate	30 Hz (Gazebo) / ~5 Hz (in telemetry)
Topic	/drone/camera

Gazebo Topics

Topic	Type	Description
/drone/cmd_vel	gz.msgs.Twist	Velocity commands
/model/drone/odometry	gz.msgs.Odometry	Drone state
/drone/camera	gz.msgs.Image	Camera images
/drone/imu	gz.msgs.IMU	IMU data

GPS-Denied Sensors

The gazebo_bridge.py converts Gazebo data to GPS-denied sensor format:

Sensor	Source
IMU	Odometry orientation + angular velocity
Altimeter	Odometry Z position
Velocity	Odometry twist
Camera	Camera sensor (base64 JPEG)
Landing Pad	Computed from relative position

Headless Mode

Run without GUI:

gz sim -s gazebo/worlds/drone_landing.sdf

Using the Launch File

For ROS 2 packages:

ros2 launch <package_name> drone_landing.launch.py

Troubleshooting

"Cannot connect to display"

export DISPLAY=:0
# or use headless mode
gz sim -s gazebo/worlds/drone_landing.sdf

Drone falls immediately

The velocity controller may need to be enabled:

gz topic -t /drone/enable -m gz.msgs.Boolean -p 'data: true'

Topics not visible in ROS

Ensure the bridge is running:

python gazebo_bridge.py

Model not found

Set the model path:

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

Camera image not in telemetry

Ensure PIL/Pillow is installed:

pip install pillow