Reuse aircraft render times and extrapolation frames

docs/CURRENT-STATE.md

@@ -1,5 +1,11 @@
 # God's Eye View Current State
 
+Civil aircraft share one delayed render timestamp per fleet update. Extrapolated
+fixes reuse their local coordinate frame until their coordinates change, including
+in-place ground-height corrections. Update cadence, contact counts, interpolation,
+turn rates and tracked-aircraft motion are unchanged. Cached frames are weakly
+keyed by each position fix and do not retain retired history.
+
 Touch-first devices use three times the default Cesium zoom sensitivity, so
 pinching traverses globe and street scales with fewer gestures. Cesium retains
 its distance-aware zoom, collision handling and minimum/maximum distance limits.

src/layers/flights/motion.js

@@ -60,6 +60,10 @@ export function createMotion({
     publishFocusTargetFromCachedPosition,
   } = services.focus;
 
+  // Fixes leave the cache with their history; corrected positions invalidate
+  // the local frame even when the existing Cartesian is mutated in place.
+  const fixFrames = new WeakMap();
+
   // Round 5: the old `_warmGroundedAircraftSurfaceCache` (global exact-5-decimal
   // warm for every grounded contact on Earth) is GONE. Parked-aircraft GPS
   // jitter minted fresh keys every poll → thousands of upstream points per
@@ -124,7 +128,7 @@ export function createMotion({
    * @returns {Cesium.Cartesian3|null} Estimated ECEF position, or null if no history exists.
    */
 
-  function _deadReckon(icao24, result) {
+  function _deadReckon(icao24, result, sampledRenderTime) {
     const info = flightState.records.data.get(icao24);
     if (FOCUS_EVIDENCE_DEV && flightState._focusEvidenceIds.has(icao24)) {
       const position = flightState._billboards.get(icao24)?.position;
@@ -149,11 +153,13 @@ export function createMotion({
     const out = result || new Cesium.Cartesian3();
     // Render one poll interval behind real time so we interpolate between
     // two KNOWN fixes whenever possible (see RENDER_DELAY_SEC rationale).
-    const renderTime = Cesium.JulianDate.addSeconds(
-      Cesium.JulianDate.now(),
-      -RENDER_DELAY_SEC,
-      flightState._scratchRenderTime,
-    );
+    const renderTime =
+      sampledRenderTime ??
+      Cesium.JulianDate.addSeconds(
+        Cesium.JulianDate.now(flightState._scratchRenderTime),
+        -RENDER_DELAY_SEC,
+        flightState._scratchRenderTime,
+      );
 
     // Bracketing pair: interpolate — no extrapolation error, no snap-back.
     for (let i = history.length - 1; i >= 1; i--) {
@@ -286,12 +292,31 @@ export function createMotion({
       0,
       flightState._scratchOffset,
     );
-    const enu = Cesium.Transforms.eastNorthUpToFixedFrame(
-      fix.position,
-      Cesium.Ellipsoid.WGS84,
-      flightState._scratchEnu,
+    let frame = fixFrames.get(fix);
+    if (!frame) {
+      frame = {
+        position: new Cesium.Cartesian3(),
+        matrix: new Cesium.Matrix4(),
+      };
+      fixFrames.set(fix, frame);
+    }
+    if (
+      !frame.valid ||
+      !Cesium.Cartesian3.equals(frame.position, fix.position)
+    ) {
+      Cesium.Transforms.eastNorthUpToFixedFrame(
+        fix.position,
+        Cesium.Ellipsoid.WGS84,
+        frame.matrix,
+      );
+      Cesium.Cartesian3.clone(fix.position, frame.position);
+      frame.valid = true;
+    }
+    return Cesium.Matrix4.multiplyByPoint(
+      frame.matrix,
+      flightState._scratchOffset,
+      out,
     );
-    return Cesium.Matrix4.multiplyByPoint(enu, flightState._scratchOffset, out);
   }
 
   /**

src/layers/flights/motion.test.mjs

@@ -0,0 +1,184 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import * as Cesium from 'cesium';
+import { createMotion } from './motion.js';
+import { arcOffsetEnu } from '../../data/motionModel.js';
+
+function fixture() {
+  const flightState = {
+    records: { data: new Map() },
+    _positionHistory: new Map(),
+    _focusEvidenceIds: new Set(),
+    _scratchArc: {},
+    _scratchOffset: new Cesium.Cartesian3(),
+    _scratchRenderTime: new Cesium.JulianDate(),
+  };
+  const motion = createMotion({
+    flightState,
+    services: { groundFloor: {}, camera: {}, focus: {} },
+    parts: {},
+  });
+  return { flightState, motion };
+}
+
+function expectedPosition(fix, dt, turnRate, transform) {
+  const arc = {};
+  arcOffsetEnu(fix.velocity, fix.track, turnRate, dt, arc);
+  return Cesium.Matrix4.multiplyByPoint(
+    transform(fix.position, Cesium.Ellipsoid.WGS84, new Cesium.Matrix4()),
+    new Cesium.Cartesian3(arc.east, arc.north, 0),
+    new Cesium.Cartesian3(),
+  );
+}
+
+function close(actual, expected) {
+  assert.ok(Cesium.Cartesian3.distance(actual, expected) < 1e-8);
+}
+
+test('extrapolation reuses fixed frames and invalidates corrected coordinates', (t) => {
+  const { motion } = fixture();
+  const transform = Cesium.Transforms.eastNorthUpToFixedFrame;
+  const spy = t.mock.method(
+    Cesium.Transforms,
+    'eastNorthUpToFixedFrame',
+    transform,
+  );
+  const fix = {
+    position: Cesium.Cartesian3.fromDegrees(-97, 30, 200),
+    velocity: 90,
+    track: 70,
+  };
+  const out = new Cesium.Cartesian3();
+  for (const dt of [-30, 5, 30, 60]) {
+    motion._extrapolateFix(fix, {}, dt, out, 1.5);
+    close(out, expectedPosition(fix, dt, 1.5, transform));
+  }
+  assert.equal(spy.mock.callCount(), 1);
+
+  // Ground reflooring mutates an existing fix's Cartesian in place.
+  Cesium.Cartesian3.fromDegrees(-97, 30, 350, undefined, fix.position);
+  motion._extrapolateFix(fix, {}, 30, out, 1.5);
+  close(out, expectedPosition(fix, 30, 1.5, transform));
+  assert.equal(spy.mock.callCount(), 2);
+
+  fix.position = Cesium.Cartesian3.fromDegrees(140, 80, 1000);
+  motion._extrapolateFix(fix, {}, 30, out, -2);
+  close(out, expectedPosition(fix, 30, -2, transform));
+  assert.equal(spy.mock.callCount(), 3);
+
+  fix.velocity = 210;
+  fix.track = 359;
+  motion._extrapolateFix(fix, {}, 15, out, -1);
+  close(out, expectedPosition(fix, 15, -1, transform));
+  assert.equal(spy.mock.callCount(), 3);
+
+  const replacement = { ...fix };
+  motion._extrapolateFix(replacement, {}, 15, out, -1);
+  close(out, expectedPosition(replacement, 15, -1, transform));
+  assert.equal(spy.mock.callCount(), 4);
+});
+
+test('stationary fixes do not build a frame until motion needs it', (t) => {
+  const { motion } = fixture();
+  const spy = t.mock.method(Cesium.Transforms, 'eastNorthUpToFixedFrame');
+  const fix = {
+    position: Cesium.Cartesian3.fromDegrees(0, 0, 0),
+    velocity: 0,
+    track: 90,
+  };
+  const out = new Cesium.Cartesian3();
+  close(motion._extrapolateFix(fix, {}, 30, out), fix.position);
+  fix.velocity = 10;
+  close(motion._extrapolateFix(fix, {}, 0, out), fix.position);
+  assert.equal(spy.mock.callCount(), 0);
+  motion._extrapolateFix(fix, {}, 30, out);
+  assert.equal(spy.mock.callCount(), 1);
+});
+
+test('fleet render time is shared without resampling or mutating the supplied instant', (t) => {
+  const { flightState, motion } = fixture();
+  const start = Cesium.JulianDate.fromIso8601('2026-10-24T12:00:00Z');
+  const end = Cesium.JulianDate.addSeconds(start, 60, new Cesium.JulianDate());
+  const renderTime = Cesium.JulianDate.addSeconds(
+    start,
+    30,
+    new Cesium.JulianDate(),
+  );
+  const savedTime = Cesium.JulianDate.clone(renderTime);
+  const history = [
+    {
+      time: start,
+      position: Cesium.Cartesian3.fromDegrees(-97, 30, 1000),
+      track: 90,
+    },
+    {
+      time: end,
+      position: Cesium.Cartesian3.fromDegrees(-96.99, 30, 1000),
+      track: 90,
+    },
+  ];
+  for (const id of ['one', 'two']) {
+    flightState.records.data.set(id, { velocity: 100, true_track: 90 });
+    flightState._positionHistory.set(id, history);
+  }
+  t.mock.method(Cesium.JulianDate, 'now', () => {
+    throw new Error('unexpected per-contact clock read');
+  });
+  const expected = Cesium.Cartesian3.lerp(
+    history[0].position,
+    history[1].position,
+    0.5,
+    new Cesium.Cartesian3(),
+  );
+  for (const id of ['one', 'two'])
+    close(
+      motion._deadReckon(id, new Cesium.Cartesian3(), renderTime),
+      expected,
+    );
+  assert.ok(Cesium.JulianDate.equals(renderTime, savedTime));
+});
+
+test('tracked callers still sample a fresh delayed time without a fleet epoch', (t) => {
+  const { flightState, motion } = fixture();
+  const start = Cesium.JulianDate.fromIso8601('2026-10-24T12:00:00Z');
+  const history = [
+    {
+      time: start,
+      position: Cesium.Cartesian3.fromDegrees(-97, 30, 1000),
+      track: 90,
+    },
+    {
+      time: Cesium.JulianDate.addSeconds(start, 60, new Cesium.JulianDate()),
+      position: Cesium.Cartesian3.fromDegrees(-96.99, 30, 1000),
+      track: 90,
+    },
+  ];
+  flightState.records.data.set('tracked', { velocity: 100, true_track: 90 });
+  flightState._positionHistory.set('tracked', history);
+  let elapsed = 60;
+  const spy = t.mock.method(Cesium.JulianDate, 'now', (result) => {
+    assert.equal(result, flightState._scratchRenderTime);
+    return Cesium.JulianDate.addSeconds(start, elapsed, result);
+  });
+  const out = new Cesium.Cartesian3();
+  close(
+    motion._deadReckon('tracked', out),
+    Cesium.Cartesian3.lerp(
+      history[0].position,
+      history[1].position,
+      0.5,
+      new Cesium.Cartesian3(),
+    ),
+  );
+  elapsed = 75;
+  close(
+    motion._deadReckon('tracked', out),
+    Cesium.Cartesian3.lerp(
+      history[0].position,
+      history[1].position,
+      0.75,
+      new Cesium.Cartesian3(),
+    ),
+  );
+  assert.equal(spy.mock.callCount(), 2);
+});

src/layers/flights/rendering.js

@@ -32,6 +32,7 @@ import {
   TRACKED_MODEL_MIN_PX,
   TRACKED_MODEL_MAX_PX,
   FLEET_DR_INTERVAL_MS,
+  RENDER_DELAY_SEC,
   COURSE_SLEW_DT_MAX_SEC,
   ROTATION_REFRESH_MS,
   COURSE_MAX_DPS,
@@ -854,6 +855,12 @@ export function createRendering({
         )
       : 0.08;
     flightState._lastFleetTickMs = nowMs;
+    // Every contact in this pass shares the same delayed display instant.
+    const renderTime = Cesium.JulianDate.addSeconds(
+      Cesium.JulianDate.now(flightState._scratchFleetRenderTime),
+      -RENDER_DELAY_SEC,
+      flightState._scratchFleetRenderTime,
+    );
 
     _drainIrReloadQueue(); // bounded per-tick slice of any pending boost-flip reload
     if (flightState._cockpitContactMode)
@@ -957,7 +964,11 @@ export function createRendering({
 
       const info = flightState.records.data.get(icao24);
 
-      const dr = parts.motion._deadReckon(icao24, flightState._scratchFleetPos);
+      const dr = parts.motion._deadReckon(
+        icao24,
+        flightState._scratchFleetPos,
+        renderTime,
+      );
       // The dead-reckoned point drifts away from the fix whose cell supplied the
       // height, so a grounded contact's sprite ends up under the mesh it taxied
       // (or coasted) over. Re-floor at the DISPLAYED coordinate — read-only, and

src/layers/flights/state.js

@@ -242,12 +242,12 @@ export function createFlightState({ source, services }) {
 
   flightState._scratchCarto = new Cesium.Cartographic();
 
-  flightState._scratchEnu = new Cesium.Matrix4();
-
   flightState._scratchArc = { east: 0, north: 0, endCourseDeg: 0 };
 
   flightState._scratchRenderTime = new Cesium.JulianDate();
 
+  flightState._scratchFleetRenderTime = new Cesium.JulianDate();
+
   flightState._scratchFleetPos = new Cesium.Cartesian3();
 
   flightState._scratchSonarScreen = new Cesium.Cartesian2();