component decomposition is done

docs/02_components/helpers/h02_gsd_calculator_spec.md

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+# 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
+