# Architecture Overview

## Modes

### 1. Standalone (1 Terminal)

```bash
python standalone_simulation.py --pattern circular
```

```
┌────────────────────────────────────────┐
│      standalone_simulation.py          │
│  PyBullet + Controllers + Camera       │
└────────────────────────────────────────┘
```

### 2. Gazebo + ROS 2 (2 Terminals)

```
Terminal 1                    Terminal 2
┌───────────────────┐        ┌───────────────────┐
│ Gazebo + Bridge   │◄──────►│ run_gazebo.py     │
└───────────────────┘  ROS   └───────────────────┘
```

### 3. ArduPilot GPS-Denied (2 Terminals)

```
Terminal 1                    Terminal 2
┌───────────────────┐        ┌───────────────────┐
│ Gazebo +          │◄──────►│ ArduPilot SITL    │
│ ArduPilot Plugin  │  JSON  │ + MAVProxy        │
└───────────────────┘        └───────────────────┘
```

## Data Flow

### Standalone
```
Controller → PyBullet → Telemetry → Controller
```

### Gazebo
```
Controller → /cmd_vel → Gazebo → /odometry → Controller
```

### ArduPilot
```
Gazebo ◄─── JSON/UDP ───► SITL ◄─── MAVLink ───► MAVProxy
```

## Key Files

| File | Purpose |
|------|---------|
| `drone_controller.py` | Your landing algorithm |
| `gazebo_bridge.py` | Gazebo ↔ ROS bridge |
| `camera_viewer.py` | Camera display |
| `config.py` | Configuration |

## GPS-Denied Sensors

| Sensor | Data |
|--------|------|
| IMU | Orientation, angular velocity |
| Altimeter | Altitude, vertical velocity |
| Camera | Downward image |
| Landing Pad | Relative position |

## Topics

| Topic | Direction |
|-------|-----------|
| `/cmd_vel` | → Drone commands |
| `/drone/telemetry` | ← Sensor data |
| `/drone/camera` | ← Camera images |