Initial Attempt

docs/gazebo.md

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+# Gazebo Simulation
+
+Running the GPS-denied drone simulation with Gazebo.
+
+## Prerequisites
+
+Install Gazebo and ROS-Gazebo bridge:
+
+```bash
+./setup/install_ubuntu.sh
+source activate.sh
+```
+
+## Quick Start
+
+**Terminal 1 - Start Gazebo:**
+```bash
+source activate.sh
+gz sim gazebo/worlds/drone_landing.sdf
+```
+
+**Terminal 2 - Spawn drone and start bridge:**
+```bash
+source activate.sh
+
+# Spawn drone
+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"'
+
+# Start bridge
+python gazebo_bridge.py
+```
+
+**Terminal 3 - Run controllers:**
+```bash
+source activate.sh
+python controllers.py --pattern circular --speed 0.3
+```
+
+## World Description
+
+The `drone_landing.sdf` world contains:
+
+| Object | Description |
+|--------|-------------|
+| Ground Plane | Infinite flat surface |
+| Sun | Directional light with shadows |
+| Landing Pad | Green box with "H" marker at origin |
+
+## Drone Model
+
+Quadrotor drone with:
+
+- **Body**: 0.3m × 0.3m × 0.1m, 1.0 kg
+- **Rotors**: 4 spinning rotors
+- **IMU**: Orientation and angular velocity
+- **Camera**: 320x240 downward-facing sensor
+- **Odometry**: Position and velocity
+
+### Gazebo Plugins
+
+| Plugin | Function |
+|--------|----------|
+| MulticopterMotorModel | Motor dynamics |
+| MulticopterVelocityControl | Velocity commands |
+| OdometryPublisher | Pose and twist |
+
+## Camera System
+
+The drone has a downward-facing camera:
+
+| Property | Value |
+|----------|-------|
+| Resolution | 320 x 240 |
+| FOV | 60 degrees |
+| Format | Base64 encoded JPEG |
+| Update Rate | 30 Hz (Gazebo) / ~5 Hz (in telemetry) |
+| Topic | `/drone/camera` |
+
+## Gazebo Topics
+
+| Topic | Type | Description |
+|-------|------|-------------|
+| `/drone/cmd_vel` | `gz.msgs.Twist` | Velocity commands |
+| `/model/drone/odometry` | `gz.msgs.Odometry` | Drone state |
+| `/drone/camera` | `gz.msgs.Image` | Camera images |
+| `/drone/imu` | `gz.msgs.IMU` | IMU data |
+
+## GPS-Denied Sensors
+
+The `gazebo_bridge.py` converts Gazebo data to GPS-denied sensor format:
+
+| Sensor | Source |
+|--------|--------|
+| IMU | Odometry orientation + angular velocity |
+| Altimeter | Odometry Z position |
+| Velocity | Odometry twist |
+| Camera | Camera sensor (base64 JPEG) |
+| Landing Pad | Computed from relative position |
+
+## Headless Mode
+
+Run without GUI:
+
+```bash
+gz sim -s gazebo/worlds/drone_landing.sdf
+```
+
+## Using the Launch File
+
+For ROS 2 packages:
+
+```bash
+ros2 launch <package_name> drone_landing.launch.py
+```
+
+## Troubleshooting
+
+### "Cannot connect to display"
+
+```bash
+export DISPLAY=:0
+# or use headless mode
+gz sim -s gazebo/worlds/drone_landing.sdf
+```
+
+### Drone falls immediately
+
+The velocity controller may need to be enabled:
+
+```bash
+gz topic -t /drone/enable -m gz.msgs.Boolean -p 'data: true'
+```
+
+### Topics not visible in ROS
+
+Ensure the bridge is running:
+
+```bash
+python gazebo_bridge.py
+```
+
+### Model not found
+
+Set the model path:
+
+```bash
+export GZ_SIM_RESOURCE_PATH=$PWD/gazebo/models:$GZ_SIM_RESOURCE_PATH
+```
+
+### Camera image not in telemetry
+
+Ensure PIL/Pillow is installed:
+```bash
+pip install pillow
+```