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| """Quadrant mapping from the OD-fovea axis. | |
| Needed for ICDR's 4-2-1 rule (severe NPDR: haemorrhages in 4 quadrants, or | |
| venous beading in 2, or IRMA in 1), which counts lesions per retinal | |
| quadrant. This module defines the four quadrants geometrically, as the | |
| roadmap specifies: one dividing line through the optic disc along the | |
| OD-fovea axis, one perpendicular to it through the same point. | |
| **Labelling deliberately avoids true anatomical nasal/temporal names.** | |
| Whether the "away from fovea" side of the OD is nasal or temporal depends on | |
| which eye (OD/OS) the image is of, and neither IDRiD nor this project's | |
| other datasets carry reliable per-image eye-laterality labels to resolve | |
| that. The labels used here -- "foveal-side" / "disc-side" for the axis- | |
| parallel direction, "superior" / "inferior" for the perpendicular one -- | |
| describe the geometry precisely without asserting an anatomical mapping | |
| this project cannot verify. A deployment with real laterality metadata | |
| could remap these to true nasal/temporal in one place (`QUADRANT_LABELS`) | |
| without touching the geometry. | |
| """ | |
| from __future__ import annotations | |
| import numpy as np | |
| __all__ = ["quadrant_axes", "assign_quadrant", "QUADRANT_LABELS"] | |
| QUADRANT_LABELS = { | |
| (1, 1): "superior-foveal-side", | |
| (1, -1): "inferior-foveal-side", | |
| (-1, 1): "superior-disc-side", | |
| (-1, -1): "inferior-disc-side", | |
| } | |
| def quadrant_axes( | |
| od_xy: tuple[float, float], fovea_xy: tuple[float, float] | |
| ) -> tuple[np.ndarray, np.ndarray]: | |
| """Unit vectors (along_axis, perpendicular_axis) through the OD, where | |
| along_axis points from OD toward the fovea. Raises if OD and fovea | |
| coincide (undefined axis) -- that should never happen for real data and | |
| signals a genuine upstream bug (e.g. a broken localisation checkpoint) | |
| if it does. | |
| """ | |
| od = np.asarray(od_xy, dtype=float) | |
| fovea = np.asarray(fovea_xy, dtype=float) | |
| axis = fovea - od | |
| norm = np.linalg.norm(axis) | |
| if norm < 1e-6: | |
| raise ValueError(f"OD and fovea coincide ({od_xy} == {fovea_xy}) -- cannot define an axis.") | |
| along = axis / norm | |
| # Perpendicular, image coordinates (y grows downward): rotate -90 degrees | |
| # so positive `perp` points toward smaller y (up the image, superior). | |
| perp = np.array([along[1], -along[0]]) | |
| return along, perp | |
| def assign_quadrant( | |
| point_xy: tuple[float, float], od_xy: tuple[float, float], fovea_xy: tuple[float, float] | |
| ) -> str: | |
| """Which of the 4 quadrants `point_xy` falls in, relative to the OD as | |
| origin and the OD-fovea line as one dividing axis. See module docstring | |
| for why the labels describe geometry, not asserted anatomy.""" | |
| along, perp = quadrant_axes(od_xy, fovea_xy) | |
| od = np.asarray(od_xy, dtype=float) | |
| v = np.asarray(point_xy, dtype=float) - od | |
| along_sign = 1 if np.dot(v, along) >= 0 else -1 | |
| perp_sign = 1 if np.dot(v, perp) >= 0 else -1 | |
| return QUADRANT_LABELS[(along_sign, perp_sign)] | |