# Gazebo Simulation

Running the GPS-denied drone simulation with Gazebo (Linux only).

## Quick Start (2 Terminals)

**Terminal 1 - Start Gazebo:**
```bash
source activate.sh
gz sim gazebo/worlds/drone_landing.sdf
```

**Terminal 2 - Run Controllers:**
```bash
source activate.sh
python run_gazebo.py --pattern circular --speed 0.3
```

## Options

```bash
python run_gazebo.py --help

Options:
  --pattern       stationary, linear, circular, square, random
  --speed, -s     Rover speed in m/s (default: 0.5)
  --amplitude, -a Movement amplitude (default: 2.0)
  --no-rover      Disable rover controller
```

## Spawning the Drone

If the drone isn't in the world, spawn it:

```bash
gz service -s /world/drone_landing_world/create \
  --reqtype gz.msgs.EntityFactory \
  --reptype gz.msgs.Boolean \
  --req 'sdf_filename: "gazebo/models/drone/model.sdf", name: "drone"'
```

## GPS-Denied Sensors

The `run_gazebo.py` script provides the same sensor interface as PyBullet:

| Sensor | Source |
|--------|--------|
| IMU | Gazebo odometry |
| Altimeter | Gazebo Z position |
| Velocity | Gazebo twist |
| Camera | Gazebo camera sensor |
| Landing Pad | Computed from relative position |

## Gazebo Topics

| Topic | Type | Description |
|-------|------|-------------|
| `/drone/cmd_vel` | `Twist` | Velocity commands |
| `/model/drone/odometry` | `Odometry` | Drone state |
| `/drone/camera` | `Image` | Camera images |

## Headless Mode

Run without GUI:

```bash
gz sim -s gazebo/worlds/drone_landing.sdf
```

## Troubleshooting

### Model not found

Set the model path:
```bash
export GZ_SIM_RESOURCE_PATH=$PWD/gazebo/models:$GZ_SIM_RESOURCE_PATH
```

### Drone falls immediately

Enable the velocity controller:
```bash
gz topic -t /drone/enable -m gz.msgs.Boolean -p 'data: true'
```

### "Cannot connect to display"

Use headless mode or WSLg:
```bash
# Headless
gz sim -s gazebo/worlds/drone_landing.sdf

# Or ensure DISPLAY is set
export DISPLAY=:0
```