# GSD Calculator Helper

## Interface Definition

**Interface Name**: `IGSDCalculator`

### Interface Methods

```python
class IGSDCalculator(ABC):
    @abstractmethod
    def compute_gsd(self, altitude: float, camera_params: CameraParameters) -> float:
        pass
    
    @abstractmethod
    def altitude_to_scale(self, altitude: float, focal_length: float) -> float:
        pass
    
    @abstractmethod
    def meters_per_pixel(self, lat: float, zoom: int) -> float:
        pass
    
    @abstractmethod
    def gsd_from_camera(self, altitude: float, focal_length: float, sensor_width: float, image_width: int) -> float:
        pass
```

## Component Description

Ground Sampling Distance computations for altitude and coordinate systems.

## API Methods

### `compute_gsd(altitude: float, camera_params: CameraParameters) -> float`

**Description**: Computes GSD from altitude and camera parameters.

**Formula**:
```
GSD = (altitude * sensor_width) / (focal_length * image_width)
```

**Example**: altitude=800m, focal=24mm, sensor=36mm, width=6000px → GSD=0.2 m/pixel

---

### `altitude_to_scale(altitude: float, focal_length: float) -> float`

**Description**: Converts altitude to scale factor for VO.

---

### `meters_per_pixel(lat: float, zoom: int) -> float`

**Description**: Computes GSD for Web Mercator tiles at zoom level.

**Formula**:
```
meters_per_pixel = 156543.03392 * cos(lat * π/180) / 2^zoom
```

**Example**: lat=48°N, zoom=19 → ~0.3 m/pixel

---

### `gsd_from_camera(altitude: float, focal_length: float, sensor_width: float, image_width: int) -> float`

**Description**: Direct GSD calculation from parameters.

## Dependencies

**External**: numpy

## Test Cases

1. Standard camera at 800m → GSD ~0.1-0.3 m/pixel
2. Web Mercator zoom 19 at Ukraine → ~0.3 m/pixel