Architecture Overview

GPS-denied drone landing simulation with multiple operation modes.

Operation Modes

1. Standalone Mode (Any Platform)

Single-process simulation - no ROS 2 or networking required:

┌────────────────────────────────────────┐
│      standalone_simulation.py          │
│  ┌──────────────────────────────────┐  │
│  │  PyBullet Physics + Camera       │  │
│  │  Built-in Landing Controller     │  │
│  │  Rover Movement Patterns         │  │
│  │  Configuration from config.py    │  │
│  └──────────────────────────────────┘  │
└────────────────────────────────────────┘

2. PyBullet + ROS 2 Mode (Two Terminals)

Terminal 1                    Terminal 2
┌──────────────────┐         ┌──────────────────────────┐
│ simulation_host  │◄─UDP───►│      run_bridge.py       │
│   (PyBullet)     │         │  ┌────────────────────┐  │
│   Port 5555      │         │  │ ROS2SimulatorBridge│  │
│                  │         │  │ DroneController    │  │
│                  │         │  │ RoverController    │  │
└──────────────────┘         │  └────────────────────┘  │
                             └──────────────────────────┘

Data flow:

RoverController publishes position → Bridge sends to Simulator
Simulator moves rover visually AND sends back telemetry
DroneController receives telemetry, publishes commands
Bridge forwards commands to Simulator

3. Gazebo + ROS 2 Mode (Two Terminals, Linux/WSL2)

Terminal 1                          Terminal 2
┌───────────────────────────┐      ┌──────────────────────────┐
│ ros2 launch ... .launch.py│      │      run_gazebo.py       │
│  ┌─────────────────────┐  │      │  ┌────────────────────┐  │
│  │ Gazebo (ign gazebo) │  │      │  │ GazeboBridge       │  │
│  │  - Drone (vel ctrl) │  │◄────►│  │ DroneController    │  │
│  │  - Rover (vel ctrl) │  │ ROS  │  │ RoverController    │  │
│  ├─────────────────────┤  │      │  └────────────────────┘  │
│  │ ros_gz_bridge       │  │      └──────────────────────────┘
│  └─────────────────────┘  │
└───────────────────────────┘

Data flow:

RoverController publishes to /rover/cmd_vel → Gazebo moves rover
Gazebo publishes odometry → GazeboBridge converts to telemetry
DroneController receives telemetry, publishes to /cmd_vel
GazeboBridge forwards to /drone/cmd_vel → Gazebo moves drone

Components

File	Description
`config.py`	Central configuration (positions, physics, gains)
`standalone_simulation.py`	All-in-one simulation
`simulation_host.py`	PyBullet physics server (UDP)
`run_bridge.py`	PyBullet bridge + controllers
`run_gazebo.py`	Gazebo bridge + controllers
`drone_controller.py`	Your landing algorithm
`rover_controller.py`	Moving landing pad
`ros_bridge.py`	ROS-UDP bridge (used by run_bridge.py)
`gazebo_bridge.py`	Gazebo-ROS bridge (used by run_gazebo.py)
`gazebo/launch/drone_landing.launch.py`	ROS 2 launch file for Gazebo
`gazebo/worlds/drone_landing.sdf`	Gazebo world with drone + rover

ROS 2 Topics

Topic	Type	Description
`/cmd_vel`	`Twist`	Drone commands from DroneController
`/drone/cmd_vel`	`Twist`	Drone commands to Gazebo
`/drone/telemetry`	`String`	GPS-denied sensor data (JSON)
`/rover/cmd_vel`	`Twist`	Rover velocity to simulator
`/rover/telemetry`	`String`	Rover position (JSON)

Network Configuration

All components default to 0.0.0.0 for network accessibility.

Remote Setup (PyBullet mode)

Machine 1 (with display):

python simulation_host.py  # Listens on 0.0.0.0:5555

Machine 2 (headless controller):

python run_bridge.py --host 192.168.1.100

UDP Ports

Port	Direction	Content
5555	Bridge → Simulator	Commands (JSON)
5556	Simulator → Bridge	Telemetry (JSON)

GPS-Denied Sensors

All modes provide the same sensor data:

Sensor	Data
IMU	Orientation (roll, pitch, yaw), angular velocity
Altimeter	Altitude above ground, vertical velocity
Velocity	Estimated velocity (x, y, z)
Camera	320x240 downward JPEG (base64)
Landing Pad	Relative position (x, y, distance) when visible

Configuration (config.py)

Section	Parameters
`DRONE`	mass, size, color, start_position, thrust/torque scales
`ROVER`	size, color, start_position, default_pattern, default_speed
`CAMERA`	width, height, fov, jpeg_quality
`PHYSICS`	gravity, timestep, telemetry_rate
`CONTROLLER`	Kp_z, Kd_z, Kp_xy, Kd_xy, rate
`LANDING`	success_distance, success_velocity, height_threshold
`NETWORK`	host, command_port, telemetry_port

Platform Support

Mode	Ubuntu	Arch	macOS	Windows	WSL2
Standalone	✅	✅	✅	✅	✅
PyBullet+ROS	✅	⚠️	❌	❌	✅
Gazebo+ROS	✅	⚠️	❌	❌	✅

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