# Architecture Overview

## Operation Modes

### 1. Standalone (Any Platform, 1 Terminal)

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

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

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

**Terminal 1:**
```bash
ros2 launch gazebo/launch/drone_landing.launch.py
```

**Terminal 2:**
```bash
python run_gazebo.py --pattern circular
```

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

### 3. ArduPilot SITL + Gazebo (2 Terminals)

**Terminal 1:**
```bash
gz sim -v4 -r ~/ardupilot_gazebo/worlds/iris_runway.sdf
```

**Terminal 2:**
```bash
sim_vehicle.py -v ArduCopter -f gazebo-iris --model JSON --console
```

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

**Key features:**
- Full ArduPilot flight controller
- EKF, stabilization, failsafes
- MAVLink protocol
- Compatible with QGroundControl, Mission Planner

## Key Components

| Component | Description |
|-----------|-------------|
| `standalone_simulation.py` | All-in-one PyBullet simulation |
| `run_gazebo.py` | Gazebo bridge + controllers |
| `drone_controller.py` | Your landing algorithm |
| `camera_viewer.py` | Camera display window |

## ROS 2 Topics (Gazebo Mode)

| Topic | Direction | Description |
|-------|-----------|-------------|
| `/drone/telemetry` | ← | Sensor data (JSON) |
| `/cmd_vel` | → | Velocity commands |
| `/drone/camera` | ← | Camera images |

## Sensors

| Sensor | Data |
|--------|------|
| IMU | orientation, angular_velocity |
| Altimeter | altitude, vertical_velocity |
| Velocity | x, y, z (m/s) |
| Camera | 320x240 image |
| Landing Pad | relative_x, relative_y (when visible) |