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api/app/core/dem.py

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+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import numpy as np
+
+from app.core.geo import PathPoint
+
+
+class DemNotConfiguredError(RuntimeError):
+    """Raised when DEM access is requested before COG data is configured."""
+
+
+def elevation_at(lat: float, lon: float, surface: str = "dtm") -> float:
+    raise DemNotConfiguredError(
+        f"DEM sampling is not configured yet for lat={lat}, lon={lon}, surface={surface}"
+    )
+
+
+def elevations_along(points: Sequence[PathPoint], surface: str = "dtm") -> np.ndarray:
+    if not points:
+        return np.array([], dtype=float)
+    raise DemNotConfiguredError(f"DEM sampling is not configured yet for surface={surface}")