# 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
```

---

## ROS 2 Launch File (Advanced)

**Location:** `gazebo/launch/drone_landing.launch.py`

This launch file automates Gazebo startup for ROS 2 integration:
1. Starts Gazebo with the world
2. Spawns the drone automatically
3. Starts `ros_gz_bridge` to connect topics

### Option 1: Direct Launch (Recommended)

Run the launch file directly with `ros2 launch`:

```bash
source activate.sh
ros2 launch gazebo/launch/drone_landing.launch.py
```

Then in another terminal, run just the controllers:
```bash
source activate.sh
python controllers.py --pattern circular
```

### Option 2: Include in Your ROS 2 Package

If you have a ROS 2 package, copy the launch file and use:
```bash
ros2 launch my_drone_package drone_landing.launch.py
```

### Launch Arguments

| Argument | Default | Description |
|----------|---------|-------------|
| `use_sim_time` | `true` | Use Gazebo clock |
| `headless` | `false` | Run without GUI |

```bash
ros2 launch gazebo/launch/drone_landing.launch.py headless:=true
```

### Topics Bridged by Launch File

| ROS 2 Topic | Description |
|-------------|-------------|
| `/drone/cmd_vel` | Velocity commands |
| `/model/drone/odometry` | Drone state |
| `/drone/imu` | IMU sensor |
| `/clock` | Simulation time |

---

## 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
```