RDC_Simulation/docs/architecture.md

Architecture Overview

GPS-denied drone landing simulation with camera vision.

System Diagram

┌─────────────────────────────────────────────────────────────────────────┐
│                         Simulation System                               │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│  ┌──────────────────┐                    ┌──────────────────────────┐   │
│  │ simulation_host  │◄── UDP:5555 ──────►│    ros_bridge.py         │   │
│  │   (PyBullet)     │                    │    (UDP ↔ ROS Bridge)    │   │
│  └──────────────────┘                    └────────────┬─────────────┘   │
│          OR                                           │                 │
│  ┌──────────────────┐                    ┌────────────┴─────────────┐   │
│  │     Gazebo       │◄── ROS Topics ────►│    gazebo_bridge.py      │   │
│  │   (Ignition)     │                    │    (Gazebo ↔ ROS Bridge) │   │
│  └──────────────────┘                    └────────────┬─────────────┘   │
│                                                       │                 │
│                                          ┌────────────▼─────────────┐   │
│                                          │    controllers.py        │   │
│                                          │  ┌─────────────────────┐ │   │
│                                          │  │  DroneController    │ │   │
│                                          │  │  RoverController    │ │   │
│                                          │  └─────────────────────┘ │   │
│                                          └──────────────────────────┘   │
└─────────────────────────────────────────────────────────────────────────┘

Components

Simulators

Component	Description
PyBullet (simulation_host.py)	Standalone physics, UDP networking, camera rendering
Gazebo	Full robotics simulator, native ROS 2 integration, camera sensor

Bridges

Component	Description
ros_bridge.py	Connects PyBullet ↔ ROS 2 via UDP
gazebo_bridge.py	Connects Gazebo ↔ ROS 2, provides same interface

Controllers

Component	Description
controllers.py	Runs drone + rover controllers together
drone_controller.py	GPS-denied landing logic
rover_controller.py	Moving landing pad patterns

ROS Topics

Topic	Type	Publisher	Subscriber
/cmd_vel	Twist	DroneController	Bridge
/drone/telemetry	String	Bridge	DroneController
/rover/telemetry	String	RoverController	DroneController
/rover/cmd_vel	Twist	RoverController	(internal)
/rover/position	Point	RoverController	(debug)

GPS-Denied Sensor Flow

Simulator                Bridge                  DroneController
    │                       │                          │
    │  Render Camera        │                          │
    │  Compute Physics      │                          │
    │──────────────────────►│                          │
    │                       │                          │
    │                       │  GPS-Denied Sensors:     │
    │                       │  - IMU                   │
    │                       │  - Altimeter             │
    │                       │  - Velocity              │
    │                       │  - Camera Image (JPEG)   │
    │                       │  - Landing Pad Detection │
    │                       │─────────────────────────►│
    │                       │                          │
    │                       │      /cmd_vel            │
    │◄──────────────────────│◄─────────────────────────│

Camera System

Both simulators provide a downward-facing camera:

Property	Value
Resolution	320 x 240
FOV	60 degrees
Format	Base64 JPEG
Update Rate	~5 Hz
Direction	Downward

Data Flow

PyBullet Mode

DroneController → /cmd_vel → ros_bridge → UDP:5555 → simulation_host
simulation_host → UDP:5556 → ros_bridge → /drone/telemetry → DroneController

Gazebo Mode

DroneController → /cmd_vel → gazebo_bridge → /drone/cmd_vel → Gazebo
Gazebo → /model/drone/odometry → gazebo_bridge → /drone/telemetry → DroneController
Gazebo → /drone/camera → gazebo_bridge → (encoded in telemetry)

UDP Protocol

Port	Direction	Content
5555	Bridge → Simulator	Command JSON
5556	Simulator → Bridge	Telemetry JSON (includes camera image)