# PyBullet Simulation

Running the GPS-denied drone simulation with PyBullet.

## Quick Start

**Terminal 1 - Simulator:**
```bash
source activate.sh
python simulation_host.py
```

**Terminal 2 - ROS Bridge:**
```bash
source activate.sh
python ros_bridge.py
```

**Terminal 3 - Controllers:**
```bash
source activate.sh
python controllers.py --pattern circular --speed 0.3
```

## Remote Setup

Run simulator on one machine, controllers on another.

**Machine 1 (with display):**
```bash
python simulation_host.py
```

**Machine 2 (headless):**
```bash
source activate.sh
python ros_bridge.py --host <MACHINE_1_IP>
python controllers.py
```

## Simulation Parameters

| Parameter | Value |
|-----------|-------|
| Physics Rate | 240 Hz |
| Telemetry Rate | 24 Hz |
| Drone Mass | 1.0 kg |
| Gravity | -9.81 m/s² |

## GPS-Denied Sensors

The simulator provides:

| Sensor | Description |
|--------|-------------|
| IMU | Orientation (roll, pitch, yaw), angular velocity |
| Altimeter | Barometric altitude, vertical velocity |
| Velocity | Optical flow estimate (x, y, z) |
| Camera | 320x240 downward JPEG image |
| Landing Pad | Vision-based relative position (60° FOV, 10m range) |

## Camera System

PyBullet renders a camera image from the drone's perspective:

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

The image is included in telemetry as `camera.image`.

## World Setup

| Object | Position | Description |
|--------|----------|-------------|
| Ground | z = 0 | Infinite plane |
| Rover | (0, 0, 0.15) | 1m × 1m landing pad |
| Drone | (0, 0, 5) | Starting position |

## UDP Communication

| Port | Direction | Data |
|------|-----------|------|
| 5555 | Bridge → Sim | Commands (JSON) |
| 5556 | Sim → Bridge | Telemetry (JSON with camera) |

## ROS Bridge Options

```bash
python ros_bridge.py --help

Options:
  --host, -H    Simulator IP (default: 127.0.0.1)
  --port, -p    Simulator port (default: 5555)
```

## Building Executable

Create standalone executable:

```bash
source activate.sh
python build_exe.py
```

Output: `dist/simulation_host` (or `.exe` on Windows)

## Troubleshooting

### "Cannot connect to X server"

PyBullet requires a display:
- Run on machine with monitor
- Use X11 forwarding: `ssh -X user@host`
- Virtual display: `xvfb-run python simulation_host.py`

### Drone flies erratically

Reduce control gains:
```python
Kp = 0.3
Kd = 0.2
```

### No telemetry received

1. Check simulator is running
2. Verify firewall allows UDP 5555-5556
3. Check IP address in ros_bridge.py

### Camera image not appearing

Ensure PIL/Pillow is installed:
```bash
pip install pillow
```