Merge pull request #1642 from bilawalsidhu/sameh/transit-floor-fix

Keep vehicles off rooftops and bridge decks by reading the 3D-tile surface where each vehicle is

changelog.d/1642-transit-floor-per-point.md

@@ -0,0 +1,7 @@
+- Keep buses and trains off rooftops and out of bridge decks on the photoreal
+  3D tiles: the ground floor probes the rendered mesh where each vehicle is,
+  keeps each reading at the point it was taken (up to sixteen a cell) and
+  answers from the reading nearest the vehicle, instead of one probe at each
+  110 m cell's centre that lifted every vehicle in the cell onto whatever lay
+  there. Transit probes each vehicle's latest point, and grounded flights read
+  the floor at their own position (Sameh Khamis, @samehkhamis, #1642).

docs/CURRENT-STATE.md

@@ -1347,6 +1347,30 @@ and snapshot source. The standalone adapter keeps the existing USGS daily feed,
 M2.5+ filtering, static discs, magnitude labels and analyst records. Disabling or
 destroying the layer cancels pending work and ignores late results.
 
+## Rendered-mesh floor readings — November 9, 2026
+
+On the photoreal stack the shared floor (`cachedGroundFloor`) answers from
+rendered-mesh readings per coarse cell (0.001°, about 110 × 80 m), sampled by
+`src/services/meshFloorSampler.js` and gated against the DEM by
+`reportValidatedMeshFloorCell` in `src/services/groundFloor.js`. The probe goes
+where the caller's point is (a vehicle or contact), not to the cell's centre;
+the sampler reads a cell at up to eight spots about 12–17 m or more apart, and
+each reading that passes the gate is kept at its point (ground snaps add theirs
+the same way; a cell keeps at most sixteen). A read answers from the cell's
+reading nearest the asked point, so a viaduct and the street beside it in one
+cell keep their own heights; two readings within about 5 m of each other keep
+the lower. A spot refused only because the cell's DEM prior was cold is tried
+again later. Transit offers the sampler the latest point of each vehicle's path
+in a cell (its newest fix in its own cell), and the grounded-flight display
+clamp reads at the contact, held inside its sticky cell. Before this, one probe
+at the cell's centre latched for the session, so a centre on a roof lifted
+everything in the cell (a Haymarket bus drew 23.5 m above the street, on the
+garage roof) and a centre in the river put Red Line trains on the Longfellow
+Bridge 6–9 m under the deck. Residual: the probe is vertical, so a vehicle
+directly under a deck or a roof overhang reads the structure above it, and a
+vehicle between readings takes the nearest one, so its floor steps where the
+nearest reading changes.
+
 ## Vessel components and sources
 
 `src/data/aisLiveVessels.js` assembles `createVesselLayer` from the
@@ -3148,7 +3172,7 @@ This is the current runtime/source-of-truth snapshot for the project.
 >   `HELD_SNAP_CONTRADICTION_M` (5 m) ABOVE the held value drops the hold and the
 >   contact is COLD again, back to the floored 2D billboard. The rule is
 >   ONE-SIDED on purpose — it targets BURIAL. A cell reading BELOW a real sample
->   is the floor chain's expected under-read (one-shot latch over ~111 m,
+>   is the floor chain's expected under-read (a few point readings over ~111 m,
 >   neighbours lean lowest, `displayFloorHeightM` only ever raises), not evidence
 >   of anything, and a two-sided cut was disproved on the track rig by a planted
 >   cell 66.7 m below a real sample at the same spot. Accepted residual, stated

src/data/flights.test.mjs

@@ -20,9 +20,11 @@ import { setMilitaryLayerActive } from './militaryRegistry.js';
 import {
   GROUND_FLOOR_LIFT_M,
   reportMeshFloorCell,
+  reportValidatedMeshFloorCell,
   setMeshFloorPreferred,
   _clearMeshFloorCellsForTest,
 } from './groundFloor.js';
+import { resolveEllipsoidalGround } from './terrainHeights.js';
 import {
   _setTrackedOverlayHostForTest,
   destroyTrackedReadout,
@@ -1181,6 +1183,39 @@ test('display floor: a grounded contact that drifted onto a higher cell is lifte
   assert.ok(Math.abs(Cesium.Math.toDegrees(c.longitude) + 97.6604) < 1e-6);
 });
 
+test('display floor: reads the reading nearest the contact, not the cell centre', async () => {
+  _clearDisplayFloorStateForTest();
+  _clearMeshFloorCellsForTest();
+  setMeshFloorPreferred(true);
+  const realFetch = globalThis.fetch;
+  globalThis.fetch = async () =>
+    new Response(JSON.stringify({ results: [{ ellipsoid: 120 }] }), {
+      status: 200,
+      headers: { 'Content-Type': 'application/json' },
+    });
+  try {
+    await resolveEllipsoidalGround([{ lat: 30.317, lon: -97.717 }]);
+  } finally {
+    globalThis.fetch = realFetch;
+  }
+  // A hangar roof over the cell's centre; the apron where the contact is.
+  assert.equal(reportValidatedMeshFloorCell(30.317, -97.717, 142), true);
+  assert.equal(reportValidatedMeshFloorCell(30.3173, -97.7173, 121), true);
+  const pos = Cesium.Cartesian3.fromDegrees(-97.7173, 30.3173, 100);
+  const out = _floorGroundedDisplayPositionForTest(
+    { onGround: true },
+    pos,
+    false,
+  );
+  const c = _floorCarto(out);
+  assert.ok(
+    Math.abs(c.height - (121 + GROUND_FLOOR_LIFT_M)) < 0.05,
+    `height ${c.height} should be the apron's 121 + lift`,
+  );
+  _clearMeshFloorCellsForTest();
+  _clearDisplayFloorStateForTest();
+});
+
 test('display floor: an AIRBORNE contact over the same cell is never lifted', () => {
   _clearDisplayFloorStateForTest();
   _clearMeshFloorCellsForTest();

src/data/groundFloor.js

@@ -22,6 +22,7 @@ export const {
   reportMeshFloorCell,
   meshFloorSampleWithinPrior,
   reportValidatedMeshFloorCell,
+  meshFloorPriorReady,
   cachedMeshFloor,
   _clearMeshFloorCellsForTest,
   cachedGroundFloor,

src/data/meshFloorSampler.test.mjs

@@ -24,7 +24,7 @@ import { sampleMeshFloorCells } from './meshFloorSampler.js';
 import { resolveEllipsoidalGround } from './terrainHeights.js';
 import {
   cachedGroundFloor, cachedMeshFloor, setMeshFloorPreferred,
-  _clearMeshFloorCellsForTest,
+  _clearMeshFloorCellsForTest, reportValidatedMeshFloorCell,
 } from './groundFloor.js';
 
 /** Distinct site per test — terrainHeights' cache is module-global and warm
@@ -137,3 +137,180 @@ test('sampler: a cell just across the antimeridian is still near the viewer', ()
   sampleMeshFloorCells(scene, [{ lat: -16.81, lon: 179.999 }], { viewerLat: -16.81, viewerLon: -179.999 });
   assert.equal(calls, 2, 'about 200 m apart, so both cells are probed');
 });
+
+test('sampler: the probe goes where the point is, not to the cell centre', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  const asked = [];
+  const scene = fakeScene((carto) => {
+    asked.push(Cesium.Math.toDegrees(carto.longitude));
+    return 122.0;
+  });
+  const point = { lat: cell.lat + 0.0003, lon: cell.lon + 0.0004 };
+  sampleMeshFloorCells(scene, [point], { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(asked.length, 1);
+  assert.ok(Math.abs(asked[0] - point.lon) < 1e-9, `probed at ${asked[0]}, not ${point.lon}`);
+});
+
+test('sampler: a viaduct and the street beside it in one cell keep their own heights', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  // A viaduct deck 9 m up along one line of the cell, the street elsewhere.
+  const deckLat = cell.lat + 0.0003;
+  let calls = 0;
+  const scene = fakeScene((carto) => {
+    calls += 1;
+    return Math.abs(Cesium.Math.toDegrees(carto.latitude) - deckLat) < 1e-7 ? 129.0 : 121.0;
+  });
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  const onDeck = { lat: deckLat, lon: cell.lon };
+  const street = { lat: cell.lat - 0.0003, lon: cell.lon };
+  sampleMeshFloorCells(scene, [onDeck], opts);
+  sampleMeshFloorCells(scene, [street], opts);
+  assert.equal(calls, 2);
+  assert.equal(cachedMeshFloor(onDeck.lat, onDeck.lon + 0.0001), 129.0, 'the train stays on the deck');
+  assert.equal(cachedMeshFloor(street.lat, street.lon - 0.0001), 121.0, 'the bus stays on the street');
+  assert.equal(cachedGroundFloor(street.lat, street.lon), 121.0);
+  sampleMeshFloorCells(scene, [{ lat: deckLat, lon: cell.lon + 0.00001 }], opts);
+  assert.equal(calls, 2, 'a point next to one already probed is not probed again');
+});
+
+test('sampler: a roof over the cell centre does not lift a bus on the street', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  // A roof 22 m up covering the cell's centre; the street 30 m west of it.
+  const scene = fakeScene((carto) =>
+    Math.abs(Cesium.Math.toDegrees(carto.longitude) - cell.lon) < 0.0001 ? 142.0 : 121.0);
+  const bus = { lat: cell.lat, lon: cell.lon - 0.0003 };
+  sampleMeshFloorCells(scene, [bus], { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(cachedGroundFloor(bus.lat, bus.lon), 121.0);
+});
+
+test('sampler: a second reading at the same spot keeps the lower one', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  assert.equal(reportValidatedMeshFloorCell(cell.lat, cell.lon, 131.0), true);
+  assert.equal(reportValidatedMeshFloorCell(cell.lat + 0.00002, cell.lon, 122.0), true);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 122.0);
+  assert.equal(reportValidatedMeshFloorCell(cell.lat, cell.lon + 0.00002, 140.0), true);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 122.0, 'a higher one never raises it');
+});
+
+test('sampler: a cell with a reading is probed a few times at most', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  let calls = 0;
+  const scene = fakeScene(() => {
+    calls += 1;
+    return 121.0;
+  });
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  for (let i = 0; i < 20; i++)
+    sampleMeshFloorCells(
+      scene,
+      [{ lat: cell.lat - 0.0004 + (i % 5) * 0.0002, lon: cell.lon - 0.00045 + Math.floor(i / 5) * 0.0003 }],
+      opts,
+    );
+  assert.equal(calls, 8);
+});
+
+test('sampler: a cell with no accepted reading is probed again on every call', async () => {
+  reset();
+  const cell = nextSite();
+  let calls = 0;
+  const scene = fakeScene(() => {
+    calls += 1;
+    return 138.0;
+  });
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  for (let i = 0; i < 3; i++) sampleMeshFloorCells(scene, [cell], opts);
+  assert.equal(calls, 3, 'no DEM prior yet, so nothing is kept and the cell is retried');
+  await seedDem(cell, 120.0);
+  sampleMeshFloorCells(scene, [cell], opts);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 138.0, 'and lands once the prior is warm');
+});
+
+test('sampler: a spot whose reading is refused does not use up the cell', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  // A tower 260 m up where the first vehicle waits; the street elsewhere and
+  // a deck 9 m up along one line of the cell.
+  const towerLon = cell.lon + 0.0004;
+  const deckLat = cell.lat + 0.0003;
+  const scene = fakeScene((carto) => {
+    if (Math.abs(Cesium.Math.toDegrees(carto.longitude) - towerLon) < 1e-7) return 380.0;
+    return Math.abs(Cesium.Math.toDegrees(carto.latitude) - deckLat) < 1e-7 ? 129.0 : 121.0;
+  });
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  for (let i = 0; i < 10; i++) sampleMeshFloorCells(scene, [{ lat: cell.lat, lon: towerLon }], opts);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'the tower is refused every time');
+  sampleMeshFloorCells(scene, [{ lat: cell.lat - 0.0003, lon: cell.lon }], opts);
+  sampleMeshFloorCells(scene, [{ lat: deckLat, lon: cell.lon - 0.0003 }], opts);
+  assert.equal(cachedMeshFloor(deckLat, cell.lon - 0.0003), 129.0, 'the deck is still probed');
+});
+
+test('ground floor: a cell keeps at most sixteen readings', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  for (let i = 0; i < 40; i++) {
+    const lat = cell.lat - 0.00045 + (i % 8) * 0.0001;
+    const lon = cell.lon - 0.00045 + Math.floor(i / 8) * 0.0002;
+    reportValidatedMeshFloorCell(lat, lon, 121.0 + i);
+  }
+  // Readings 0..15 are kept; reading 39 (at the far corner) is not, so that
+  // spot answers from the nearest kept one.
+  assert.equal(cachedMeshFloor(cell.lat - 0.00045, cell.lon - 0.00045), 121.0);
+  assert.equal(cachedMeshFloor(cell.lat + 0.00025, cell.lon + 0.00035), 121.0 + 15);
+});
+
+test('sampler: a spot refused while the DEM was cold is probed again once it is warm', async () => {
+  reset();
+  const cell = nextSite();
+  const deckLat = cell.lat + 0.0003;
+  let calls = 0;
+  const scene = fakeScene((carto) => {
+    calls += 1;
+    return Math.abs(Cesium.Math.toDegrees(carto.latitude) - deckLat) < 1e-7 ? 129.0 : 121.0;
+  });
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  const onDeck = { lat: deckLat, lon: cell.lon };
+  sampleMeshFloorCells(scene, [onDeck], opts);
+  assert.equal(cachedMeshFloor(onDeck.lat, onDeck.lon), null, 'no prior, nothing kept');
+  await seedDem(cell, 120.0);
+  sampleMeshFloorCells(scene, [{ lat: cell.lat - 0.0003, lon: cell.lon }], opts);
+  sampleMeshFloorCells(scene, [onDeck], opts);
+  assert.equal(calls, 3);
+  assert.equal(cachedMeshFloor(onDeck.lat, onDeck.lon), 129.0);
+});
+
+test('sampler: a spot refused while the DEM prior was evicted is probed again', async () => {
+  const { createGroundFloor } = await import('../services/groundFloor.js');
+  const { createMeshFloorSampler } = await import('../services/meshFloorSampler.js');
+  let prior = 120.0;
+  const terrain = {
+    cachedRealEllipsoidalGround: () => prior,
+    resolveEllipsoidalGround: async () => {},
+  };
+  const groundFloor = createGroundFloor({ terrain });
+  const sampler = createMeshFloorSampler({ groundFloor });
+  const cell = { lat: 41.5, lon: -97.66 };
+  const deckLat = cell.lat + 0.0003;
+  const scene = fakeScene((carto) =>
+    Math.abs(Cesium.Math.toDegrees(carto.latitude) - deckLat) < 1e-7 ? 129.0 : 121.0);
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  const onDeck = { lat: deckLat, lon: cell.lon };
+  sampler.sampleMeshFloorCells(scene, [{ lat: cell.lat - 0.0003, lon: cell.lon }], opts);
+  prior = null; // the cell's DEM entry is evicted; the street reading stays
+  sampler.sampleMeshFloorCells(scene, [onDeck], opts);
+  assert.equal(groundFloor.cachedMeshFloor(onDeck.lat, onDeck.lon), 121.0);
+  prior = 120.0;
+  sampler.sampleMeshFloorCells(scene, [onDeck], opts);
+  assert.equal(groundFloor.cachedMeshFloor(onDeck.lat, onDeck.lon), 129.0);
+});

src/layers/cctv/geometry.js

@@ -448,7 +448,7 @@ export function createGeometry({ state: layerState, services, parts, source }) {
     }
 
     // Photoreal regime. Sampling is delegated to the shared coarse-cell
-    // sampler. It remains event-driven, one-shot per cell, and keeps its
+    // sampler. It remains event-driven, a few probes per cell, and keeps its
     // existing acceptance window; CCTV adds no rooftop rejection policy.
     if (sampleGround && parts.model.projectionTilesReady()) {
       record.groundMeshSampleRequestCount =

src/layers/flights/motion.js

@@ -37,6 +37,22 @@ import {
   DISPLAY_CORRIDOR_FAIR_SHARE,
 } from './policy.js';
 
+/** Half a coarse floor cell (0.001°), less a margin so rounding keeps a
+ *  clamped coordinate inside the cell. */
+const HALF_CELL_DEG = 0.00049;
+
+/**
+ * A coordinate held within half a cell of the cell's centre (the short way
+ * round for longitude), so a read lands in the given cell.
+ * @param {number} deg @param {number} centreDeg
+ * @returns {number}
+ */
+function clampToCell(deg, centreDeg) {
+  let d = deg - centreDeg;
+  d -= 360 * Math.round(d / 360);
+  return centreDeg + Math.max(-HALF_CELL_DEG, Math.min(HALF_CELL_DEG, d));
+}
+
 export function createMotion({
   flightState,
   services,
@@ -865,12 +881,15 @@ export function createMotion({
     );
     // Boundary hysteresis: a position jittering across a cell edge would flip
     // floors at fleet-tick rate (see stickyFloorCell).
-    const cell = stickyFloorCell(
-      Cesium.Math.toDegrees(carto.latitude),
-      Cesium.Math.toDegrees(carto.longitude),
-      state?.cell,
+    const latDeg = Cesium.Math.toDegrees(carto.latitude);
+    const lonDeg = Cesium.Math.toDegrees(carto.longitude);
+    const cell = stickyFloorCell(latDeg, lonDeg, state?.cell);
+    // A cell holds rendered-surface readings at the points they were taken,
+    // so the floor is read where the contact is, held inside its sticky cell.
+    const floor = cachedGroundFloor(
+      clampToCell(latDeg, cell.lat),
+      clampToCell(lonDeg, cell.lon),
     );
-    const floor = cachedGroundFloor(cell.lat, cell.lon);
     const next = state || {
       cell,
       in: new Cesium.Cartesian3(),

src/layers/flights/snapshotRenderer.js

@@ -300,8 +300,8 @@ export function createFlightSnapshotRenderer({
     // floor cells collected in the loop (fire-and-forget, single-flight;
     // read synchronously by NEXT poll's clamp — the military-layer pattern).
     warmGroundFloor(floorWarmPoints);
-    // Round 4: sample the RENDERED mesh for those same cells (one-shot per
-    // cell, budget-capped, viewer-proximate, google-3d regime only). Own
+    // Round 4: sample the RENDERED mesh for those same cells (a few probes
+    // per cell, budget-capped, viewer-proximate, google-3d regime only). Own
     // billboards/models are excluded so a vertical probe can't land on an
     // aircraft instead of the pavement.
     sampleMeshFloorCells(flightState._viewer?.scene, floorWarmPoints, {

src/layers/military/snapshotRenderer.js

@@ -228,8 +228,8 @@ export function createMilitarySnapshotRenderer({
       const bbStale = flightState._billboards.get(icao24);
       if (bbStale) bbStale.position = liftedPos;
     }
-    // Round 4: sample the RENDERED mesh for those cells (one-shot per cell,
-    // budget-capped, viewer-proximate, google-3d regime only), excluding
+    // Round 4: sample the RENDERED mesh for those cells (a few probes per
+    // cell, budget-capped, viewer-proximate, google-3d regime only), excluding
     // this layer's own billboards/models from the probe.
     {
       const viewerCarto =

src/layers/transit/height.js

@@ -124,7 +124,14 @@ export function createHeight({ state, services, parts }) {
       const cells = new Map();
       const collect = (point, answer) => {
         if (!onGround) return;
-        if (!cells.has(answer.cell))
+        // A cell keeps the last point offered in it: the path is walked
+        // oldest first, so that is where the vehicle is now or about to be,
+        // and the mesh sampler reads the surface there.
+        const held = cells.get(answer.cell);
+        if (held) {
+          held.lat = point.lat;
+          held.lon = point.lon;
+        } else
           cells.set(answer.cell, {
             lat: point.lat,
             lon: point.lon,
@@ -136,6 +143,13 @@ export function createHeight({ state, services, parts }) {
       const newest = entry.fixes.at(-1);
       const answer = requestHeight(newest.lat, newest.lon, entry);
       entry.heightCell = answer.cell;
+      // The selected vehicle's path also offers its history, newest segment
+      // first; the vehicle's own cell is read where its newest fix is.
+      const own = cells.get(answer.cell);
+      if (own) {
+        own.lat = newest.lat;
+        own.lon = newest.lon;
+      }
       if (answer.height !== null) {
         entry.heightM = answer.height;
         entry.heightResolved = true;

src/layers/transit/lifecycle.test.mjs

@@ -2938,6 +2938,114 @@ test('mesh refinement reaches all 100 retained DEM cells within five poll budget
   assert.equal(probed.size, 100);
 });
 
+test('mesh refinement probes the latest point the path offers in a cell', async (t) => {
+  const { createHeight } = await import('./height.js');
+  // Three points along one cell's stretch of path, oldest first.
+  const path = [
+    { lat: 42.3611, lon: -71.0751 },
+    { lat: 42.3612, lon: -71.0753 },
+    { lat: 42.3614, lon: -71.0754 },
+  ];
+  const entry = { key: 'train', to: path[0], fixes: [path.at(-1)] };
+  const probed = [];
+  const state = {
+    _enabled: true,
+    _selectedKey: null,
+    _visible: new Set([entry]),
+    _vehicles: new Map([[entry.key, entry]]),
+    _floorCursor: 0,
+    _heightDirty: new Set(),
+    _viewer: { camera: { positionCartographic: { height: 100 } } },
+  };
+  const height = createHeight({
+    state,
+    services: {
+      render: { governorRequestRender() {} },
+      ground: {
+        coarseFloorCoord: (lat, lon) => ({
+          lat: Number(lat.toFixed(3)),
+          lon: Number(lon.toFixed(3)),
+        }),
+        cachedGroundFloor: () => 10,
+        GROUND_FLOOR_LIFT_M: 1.5,
+      },
+      mesh: {
+        sampleMeshFloorCells(scene, points) {
+          probed.push(...points.map((p) => [p.lat, p.lon]));
+        },
+      },
+    },
+    parts: {
+      trails: {
+        prepareEntry(e, collect) {
+          if (collect)
+            for (const point of path)
+              collect(point, height.requestHeight(point.lat, point.lon));
+        },
+      },
+      rendering: { requestVisibility() {} },
+    },
+  });
+  t.after(() => height.clear());
+  height.anchorFloors();
+  assert.deepEqual(probed, [[42.3614, -71.0754]]);
+});
+
+test('the selected vehicle is probed at its newest fix in its own cell', async (t) => {
+  const { createHeight } = await import('./height.js');
+  // The selected path offers its active corridor first, then its history
+  // newest segment first, so the last offer in the cell is an older point.
+  const newest = { lat: 42.3614, lon: -71.0754 };
+  const offers = [
+    newest,
+    { lat: 42.3612, lon: -71.0753 },
+    { lat: 42.3611, lon: -71.0751 },
+  ];
+  const entry = { key: 'train', to: offers[0], fixes: [newest] };
+  const probed = [];
+  const state = {
+    _enabled: true,
+    _selectedKey: entry.key,
+    _visible: new Set([entry]),
+    _vehicles: new Map([[entry.key, entry]]),
+    _floorCursor: 0,
+    _heightDirty: new Set(),
+    _viewer: { camera: { positionCartographic: { height: 100 } } },
+  };
+  const height = createHeight({
+    state,
+    services: {
+      render: { governorRequestRender() {} },
+      ground: {
+        coarseFloorCoord: (lat, lon) => ({
+          lat: Number(lat.toFixed(3)),
+          lon: Number(lon.toFixed(3)),
+        }),
+        cachedGroundFloor: () => 10,
+        GROUND_FLOOR_LIFT_M: 1.5,
+      },
+      mesh: {
+        sampleMeshFloorCells(scene, points) {
+          probed.push(...points.map((p) => [p.lat, p.lon]));
+        },
+      },
+    },
+    parts: {
+      trails: {
+        prepareEntry(e, collect) {
+          if (collect)
+            for (const point of offers)
+              collect(point, height.requestHeight(point.lat, point.lon));
+        },
+      },
+      rendering: { requestVisibility() {} },
+    },
+  });
+  t.after(() => height.clear());
+  height.anchorFloors();
+  assert.deepEqual(probed, [[42.3614, -71.0754]]);
+});
+
 test('selection churn releases past geometry on every retained vehicle', async (t) => {
   const app = harness(t, { floorAt: () => 10 });
   const { mergeHistory, seek } = await import('../../data/contactPlayback.js');

src/services/groundFloor.js

@@ -418,13 +418,26 @@ export function createGroundFloor({ terrain, signal }) {
   // is the photogrammetric MESH, which sits above it (measured ~17 m at the
   // Austin airport apron). DEM-flooring therefore still buried sprites/trails
   // inside the mesh. These cells hold the RENDERED surface height, sampled
-  // one-shot per coarse cell near the viewer (scene.sampleHeight — the same
+  // at the callers' points, a few per coarse cell near the viewer, each kept
+  // where it was taken and read back from the nearest (scene.sampleHeight — the same
   // source groundSnap uses, which is why 3D models always looked right) and
   // reported here by meshFloorSampler.js. Design principle (owner): NEVER
   // below the visible surface; slightly above is always fine. The DEM stays
   // the instant global prior/fallback and the sanity gate for samples.
-  /** @type {Map<string, number>} coarse cell key -> rendered-surface height (m, ellipsoidal). */
+  /** @type {Map<string, Array<{lat: number, lon: number, h: number}>>}
+   *  coarse cell key -> rendered-surface readings (m, ellipsoidal), each kept
+   *  at the point it was probed. A read answers from the reading nearest the
+   *  asked point, so a viaduct and the street beside it in one cell keep their
+   *  own heights. */
   const _meshCells = new Map();
+  /** @constant {number} Readings closer than this (degrees, about 5 m) are
+   *  one spot: the lower one is kept there. */
+  const MESH_READING_SAME_SPOT_DEG = 0.00005;
+  /** @constant {number} Readings kept per cell. The sampler probes a cell at
+   *  most eight times, but ground snaps report at each aircraft's position;
+   *  past this many, a reading away from the others is not kept, so a busy
+   *  apron cell stays a short list to scan. */
+  const MESH_READINGS_PER_CELL = 16;
   /** @type {boolean} Whether mesh cells apply — true only in the google-3d
    *  regime (photoreal stack). On globe stacks the rendered surface IS the
    *  terrain provider (Re:Earth on keyless), so the DEM is already correct
@@ -444,7 +457,8 @@ export function createGroundFloor({ terrain, signal }) {
 
   /**
    * Records a sampled rendered-surface height for the cell containing the
-   * coordinate (one-shot latch — first accepted sample wins).
+   * coordinate, unchecked, when the cell has no reading yet. The sampler goes
+   * through `reportValidatedMeshFloorCell`, which keeps a reading per point.
    * @param {number} lat @param {number} lon @param {number} heightM
    */
   function reportMeshFloorCell(lat, lon, heightM) {
@@ -456,7 +470,7 @@ export function createGroundFloor({ terrain, signal }) {
       return;
     const c = coarseFloorCoord(lat, lon);
     const key = `${c.lat},${c.lon}`;
-    if (!_meshCells.has(key)) _meshCells.set(key, heightM);
+    if (!_meshCells.has(key)) _meshCells.set(key, [{ lat, lon, h: heightM }]);
   }
 
   /** Return whether a rendered-mesh sample is plausible against a real DEM prior. */
@@ -471,9 +485,11 @@ export function createGroundFloor({ terrain, signal }) {
 
   /**
    * Validate and record a rendered-mesh floor through the single shared gate.
-   * Callers must not bypass this with raw `reportMeshFloorCell`: a coarse-LOD,
-   * rooftop, or aircraft hit would otherwise win the session-long first-write
-   * latch and poison every floor consumer in the cell.
+   * Callers must not bypass this with raw `reportMeshFloorCell`: a coarse-LOD
+   * or aircraft hit would otherwise poison every floor consumer in the cell.
+   * The reading is kept at the point it was taken; a second reading at the
+   * same spot (within about 5 m) keeps the lower of the two. A cell keeps at
+   * most MESH_READINGS_PER_CELL readings.
    * @returns {boolean} Whether the sample passed and was reported.
    */
   function reportValidatedMeshFloorCell(lat, lon, heightM) {
@@ -481,13 +497,41 @@ export function createGroundFloor({ terrain, signal }) {
     const cell = coarseFloorCoord(lat, lon);
     const prior = cachedRealEllipsoidalGround(cell.lat, cell.lon);
     if (!meshFloorSampleWithinPrior(heightM, prior)) return false;
-    reportMeshFloorCell(cell.lat, cell.lon, heightM);
+    const key = `${cell.lat},${cell.lon}`;
+    const readings = _meshCells.get(key);
+    if (!readings) {
+      _meshCells.set(key, [{ lat, lon, h: heightM }]);
+      return true;
+    }
+    const same = readings.find(
+      (r) =>
+        Math.abs(r.lat - lat) < MESH_READING_SAME_SPOT_DEG &&
+        Math.abs(r.lon - lon) < MESH_READING_SAME_SPOT_DEG,
+    );
+    if (same) {
+      if (heightM < same.h) same.h = heightM;
+    } else if (readings.length < MESH_READINGS_PER_CELL) {
+      readings.push({ lat, lon, h: heightM });
+    }
     return true;
   }
 
   /**
-   * Synchronous mesh-cell read — null when the cell is unsampled OR the
-   * google-3d regime is inactive (globe stacks must floor on the DEM).
+   * Whether the cell holding the point has the real DEM prior that
+   * `reportValidatedMeshFloorCell` judges a reading against.
+   * @param {number} lat @param {number} lon
+   * @returns {boolean}
+   */
+  function meshFloorPriorReady(lat, lon) {
+    if (!Number.isFinite(lat) || !Number.isFinite(lon)) return false;
+    const c = coarseFloorCoord(lat, lon);
+    return cachedRealEllipsoidalGround(c.lat, c.lon) != null;
+  }
+
+  /**
+   * Synchronous mesh-cell read — the cell's reading nearest the point, or
+   * null when the cell is unsampled OR the google-3d regime is inactive (globe
+   * stacks must floor on the DEM).
    * @param {number} lat @param {number} lon
    * @returns {number|null}
    */
@@ -495,8 +539,20 @@ export function createGroundFloor({ terrain, signal }) {
     if (!_meshPreferred) return null;
     if (!Number.isFinite(lat) || !Number.isFinite(lon)) return null;
     const c = coarseFloorCoord(lat, lon);
-    const h = _meshCells.get(`${c.lat},${c.lon}`);
-    return h != null ? h : null;
+    const readings = _meshCells.get(`${c.lat},${c.lon}`);
+    if (!readings) return null;
+    if (readings.length === 1) return readings[0].h;
+    const k = Math.cos((lat * Math.PI) / 180) ** 2;
+    let best = readings[0],
+      bestD = Infinity;
+    for (const r of readings) {
+      const d = (r.lat - lat) ** 2 + k * (r.lon - lon) ** 2;
+      if (d < bestD) {
+        bestD = d;
+        best = r;
+      }
+    }
+    return best.h;
   }
 
   /** Test hook: clears mesh cells (never called at runtime — cells are valid all session). */
@@ -662,6 +718,7 @@ export function createGroundFloor({ terrain, signal }) {
     reportMeshFloorCell,
     meshFloorSampleWithinPrior,
     reportValidatedMeshFloorCell,
+    meshFloorPriorReady,
     cachedMeshFloor,
     _clearMeshFloorCellsForTest,
     cachedGroundFloor,

src/services/groundSnap.js

@@ -101,7 +101,7 @@ const HELD_SNAP_MAX_DRIFT_M = 250;
  *  alone, and the asymmetry is not tidiness:
  *
  *   - A cell reading LOW against a real sample is the EXPECTED error here, not a
- *     contradiction. Cells are a one-shot first-write latch over ~111 m, the
+ *     contradiction. Cells hold a few point readings over ~111 m, the
  *     borrowed-neighbour path leans to the LOWEST on purpose (`neighborFloorM`),
  *     and `displayFloorHeightM` only ever RAISES — the whole floor chain is
  *     built to under-read rather than to invent. Releasing on that sign would

src/services/meshFloorSampler.js

@@ -11,6 +11,7 @@ export function createMeshFloorSampler({
     coarseFloorCoord,
     cachedMeshFloor,
     reportValidatedMeshFloorCell,
+    meshFloorPriorReady,
     setMeshFloorPreferred,
     meshFloorPreferred,
     cachedGroundFloor,
@@ -23,13 +24,16 @@ export function createMeshFloorSampler({
   // which sits above the Re:Earth bare-earth DEM (measured ~17 m at the Austin
   // airport apron) — so DEM-floored sprites/trails still buried themselves in
   // the mesh while 3D models (which groundSnap against the mesh) looked right.
-  // This module samples the mesh height ONE-SHOT per coarse cell and reports it
-  // to groundFloor.js, whose cachedGroundFloor() then answers mesh-first.
+  // This module samples the mesh height at the callers' points, a few probes
+  // per coarse cell, and reports them to groundFloor.js, which keeps each
+  // reading that passes its gate at its own point; cachedGroundFloor() then
+  // answers mesh-first, from the reading nearest the asked point.
   //
   // Rationing (the CCTV loading-jitter lesson): scene.sampleHeight forces
   // tile-load prioritization at the probe point, so sampling is (a) gated to
   // cells NEAR the viewer — where tiles are streamed and where an error is
-  // visible at all, (b) capped per call, (c) one-shot per cell for the session,
+  // visible at all, (b) capped per call, (c) at most MAX_PROBES_PER_CELL
+  // readings per cell for the session, each at a point apart from the others,
   // (d) skipped entirely outside the google-3d regime. A returned-undefined
   // probe (tiles not streamed yet) is NOT latched — it retries on a later call.
   //
@@ -49,6 +53,16 @@ export function createMeshFloorSampler({
    *  streamed LOD under a high camera is coarse everywhere, so every probe
    *  would latch junk. */
   const MAX_CAMERA_HEIGHT_M = 25_000;
+  /** @constant {number} Readings per cell: a cell is probed at most this
+   *  many times, each at a point apart from the others, and groundFloor keeps
+   *  each reading at its point (a read answers from the nearest one). */
+  const MAX_PROBES_PER_CELL = 8;
+  /** @constant {number} How far apart (degrees, about 17 m) a new probe must
+   *  be from the cell's earlier ones to be worth taking. */
+  const PROBE_APART_DEG = 0.00015;
+  /** @type {Map<string, Array<{lat: number, lon: number}>>} Points probed
+   *  per cell that returned a reading. */
+  const _probedPoints = new Map();
   /** @type {Cesium.Cartographic} Scratch for probe coordinates. */
   const _scratchProbe = new Cesium.Cartographic();
 
@@ -82,7 +96,7 @@ export function createMeshFloorSampler({
 
   /**
    * Samples the rendered mesh height for the coarse cells containing `points`,
-   * one-shot per cell, budget-capped, viewer-proximity-gated. Call ONCE per
+   * a few probes per cell, budget-capped, viewer-proximity-gated. Call ONCE per
    * layer poll (never per contact, never per frame). Synchronous — Cesium's
    * sampleHeight is a CPU-side query against loaded tiles.
    *
@@ -119,8 +133,21 @@ export function createMeshFloorSampler({
       const cell = coarseFloorCoord(p.lat, p.lon);
       const key = `${cell.lat},${cell.lon}`;
       if (attempted.has(key)) continue;
+      // A cell with a reading is probed again only at a point well apart
+      // from the ones already probed, a few times at most, so the cell's
+      // readings follow where its vehicles actually are.
+      const probes = _probedPoints.get(key);
+      if (
+        cachedMeshFloor(cell.lat, cell.lon) != null &&
+        (probes?.length >= MAX_PROBES_PER_CELL ||
+          probes?.some(
+            (q) =>
+              Math.abs(q.lat - p.lat) < PROBE_APART_DEG &&
+              Math.abs(q.lon - p.lon) < PROBE_APART_DEG,
+          ))
+      )
+        continue;
       attempted.add(key);
-      if (cachedMeshFloor(cell.lat, cell.lon) != null) continue; // one-shot latch
       if (
         Number.isFinite(viewerLat) &&
         Number.isFinite(viewerLon) &&
@@ -131,9 +158,11 @@ export function createMeshFloorSampler({
       }
       let height;
       try {
+        // Probe where the caller's point is, not at the cell's centre: a
+        // centre that falls on a roof would lift everything in the cell.
         const carto = Cesium.Cartographic.fromDegrees(
-          cell.lon,
-          cell.lat,
+          p.lon,
+          p.lat,
           0,
           _scratchProbe,
         );
@@ -171,7 +200,23 @@ export function createMeshFloorSampler({
       // feasible and deliberately deferred — see the P2 in
       // the project roadmap, which bundles it with the fly_route probe so
       // one post-launch pass settles rendered-mesh sampling everywhere.
-      reportValidatedMeshFloorCell(cell.lat, cell.lon, height);
+      const accepted = reportValidatedMeshFloorCell(p.lat, p.lon, height);
+      // A spot counts as probed once the gate has judged it against a real
+      // prior: accepted, or refused with the cell's DEM warm. A spot refused
+      // only because the DEM was still cold is tried again later. Each spot is
+      // recorded once, so a cell retried while it has no reading does not fill
+      // its probe allowance with the same spot.
+      if (!accepted && !meshFloorPriorReady(cell.lat, cell.lon)) continue;
+      if (!probes) _probedPoints.set(key, [{ lat: p.lat, lon: p.lon }]);
+      else if (
+        probes.length < MAX_PROBES_PER_CELL &&
+        !probes.some(
+          (q) =>
+            Math.abs(q.lat - p.lat) < PROBE_APART_DEG &&
+            Math.abs(q.lon - p.lon) < PROBE_APART_DEG,
+        )
+      )
+        probes.push({ lat: p.lat, lon: p.lon });
     }
   }