Release God's Eye View as open source

src/data/issPass.js

@@ -0,0 +1,66 @@
+// src/data/issPass.js
+/**
+ * Next-ISS-pass prediction from a satrec: coarse 30 s scan to find a window
+ * where elevation ≥ minElevDeg, refined to ~5 s at the edges, tracking peak
+ * elevation. ~2880 SGP4 propagations for a 24 h horizon — tens of ms, fine for
+ * an on-demand voice call. Pattern from skylight (MIT) shared/src/celestial.ts
+ * nextISSPass, extended with set-time + peak tracking.
+ */
+import { propagate, gstime, eciToEcf, ecfToLookAngles } from 'satellite.js';
+
+const R2D = 180 / Math.PI;
+const D2R = Math.PI / 180;
+
+/** Observer look angles at an instant, or null when propagation fails. */
+export function lookAnglesAt(satrec, dateMs, latDeg, lonDeg) {
+  const date = new Date(dateMs);
+  const pv = propagate(satrec, date);
+  const pos = pv && pv.position;
+  if (!pos || typeof pos === 'boolean') return null;
+  const ecf = eciToEcf(pos, gstime(date));
+  const look = ecfToLookAngles(
+    { latitude: latDeg * D2R, longitude: lonDeg * D2R, height: 0 },
+    ecf,
+  );
+  return {
+    elevDeg: look.elevation * R2D,
+    azDeg: (((look.azimuth * R2D) % 360) + 360) % 360,
+  };
+}
+
+export function findNextIssPass({
+  satrec, latDeg, lonDeg, fromMs,
+  minElevDeg = 10, horizonHours = 24, coarseStepSec = 30, fineStepSec = 5,
+}) {
+  const elev = (t) => lookAnglesAt(satrec, t, latDeg, lonDeg)?.elevDeg ?? -90;
+  const horizonMs = fromMs + horizonHours * 3600_000;
+  const coarse = coarseStepSec * 1000;
+  const fine = fineStepSec * 1000;
+
+  // Coarse scan for the first sample above threshold. If we START inside a
+  // pass, that's still "the next pass" for a voice answer — accept it.
+  let hit = null;
+  for (let t = fromMs; t <= horizonMs; t += coarse) {
+    if (elev(t) >= minElevDeg) { hit = t; break; }
+  }
+  if (hit == null) return null;
+
+  // Refine rise: walk back in fine steps to the first sample ≥ threshold.
+  let riseMs = hit;
+  while (riseMs - fine > fromMs && elev(riseMs - fine) >= minElevDeg) riseMs -= fine;
+
+  // Walk forward through the pass tracking the peak until we drop below.
+  let maxElevDeg = -90;
+  let maxElevMs = riseMs;
+  let t = riseMs;
+  while (t <= horizonMs) {
+    const e = elev(t);
+    if (e < minElevDeg && t > riseMs) break;
+    if (e > maxElevDeg) { maxElevDeg = e; maxElevMs = t; }
+    t += fine;
+  }
+  const setMs = t;
+
+  const rise = lookAnglesAt(satrec, riseMs, latDeg, lonDeg);
+  return { riseMs, setMs, maxElevDeg, maxElevMs, riseAzDeg: rise ? rise.azDeg : 0 };
+}