araharah-executor
3e0c5e3eb4
- geo.ts: haversineM + deriveCumulativeDistanceM (D-07 snapped-progress field) - fixture-source.ts: backend #1 — ORIGIN_TOLERANCE_M=200 matching law, honest-null pending semantics (D-03), defensive pair skip at index build, lazy memoized index (LAW 1), static JSON import (LAW 2), zero logging/storage/network (LAW 3, D-12) - index.ts: named-export public surface, subpath-with-extension import law - loader proven in three environments (bare Node 24, esbuild, Vite-family)
50 lines
2.1 KiB
TypeScript
50 lines
2.1 KiB
TypeScript
/*
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* geo.ts — spherical geo math for the route model (D-07).
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* --------------------------------------------------------
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* haversineM: great-circle distance in meters on the mean-earth sphere
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* (radius 6 371 000 m — at KL-metro scale the model error is far below the
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* fixture corpus's 200 m origin tolerance). Finite for finite inputs.
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*
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* deriveCumulativeDistanceM: the snapped-progress support field (D-07 — the
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* GUID-05/06 upstream obligation). Produces [0, d(p0→p1), d(p0→p1)+d(p1→p2),
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* …] — the same length as the input, [0] === 0, non-decreasing. Phase 6's
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* guidance snaps a live fix's progress along the line using this array
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* instead of re-deriving it per fix; the fixture source derives it once at
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* decode/load and memoizes (RESEARCH Finding 1).
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*
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* Pure: no I/O, no logging, no storage (the D-15 analog — nothing about a
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* request outlives the caller's frame).
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*/
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import type { RoutePoint } from "./types.ts";
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const EARTH_RADIUS_M = 6_371_000;
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const DEGREES_TO_RADIANS = Math.PI / 180;
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/** Great-circle distance between two WGS84 points, in meters. */
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export function haversineM(a: RoutePoint, b: RoutePoint): number {
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const lat1 = a.lat * DEGREES_TO_RADIANS;
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const lat2 = b.lat * DEGREES_TO_RADIANS;
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const dLat = (b.lat - a.lat) * DEGREES_TO_RADIANS;
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const dLng = (b.lng - a.lng) * DEGREES_TO_RADIANS;
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const sinLat = Math.sin(dLat / 2);
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const sinLng = Math.sin(dLng / 2);
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const h = sinLat * sinLat + Math.cos(lat1) * Math.cos(lat2) * sinLng * sinLng;
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return 2 * EARTH_RADIUS_M * Math.asin(Math.min(1, Math.sqrt(h)));
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}
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/** Meters walked along the polyline: same length as points, [0] === 0,
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* non-decreasing. Empty -> []; single point -> [0]. */
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export function deriveCumulativeDistanceM(points: readonly RoutePoint[]): number[] {
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if (points.length === 0) return [];
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const cumulative: number[] = [0];
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for (let i = 1; i < points.length; i++) {
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const prev = points[i - 1];
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const curr = points[i];
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const prevMeters = cumulative[i - 1];
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if (prev === undefined || curr === undefined || prevMeters === undefined) break;
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cumulative.push(prevMeters + haversineM(prev, curr));
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}
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return cumulative;
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}
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