diff --git a/scripts/package-boundaries.json b/scripts/package-boundaries.json
index 3ebc8fdfb..6c9f600a6 100644
--- a/scripts/package-boundaries.json
+++ b/scripts/package-boundaries.json
@@ -1559,7 +1559,13 @@
       "src/layers/firms/queries.js",
       "src/layers/firms/rendering.js",
       "src/data/entityRecords.js",
+      "src/data/iconSetPrimitive.js",
+      "src/data/iconSet.js",
+      "src/data/iconSegment.js",
+      "src/data/iconAtlas.js",
+      "src/data/aircraftRecession.js",
       "src/data/billboardMirror.js",
+      "src/data/motionModel.js",
       "src/layers/firms/selection.js",
       "src/layers/firms/source.js",
       "src/layers/firms/state.js",
diff --git a/src/data/firmsHeatmap.js b/src/data/firmsHeatmap.js
index 95fed982d..1b63b3394 100644
--- a/src/data/firmsHeatmap.js
+++ b/src/data/firmsHeatmap.js
@@ -16,7 +16,6 @@ const helpers = createFirmsHelpers({
 });
 export const mapAnalystRecord = helpers.mapAnalystRecord;
 export const fireCullPosition = helpers.fireCullPosition;
-export const applyHorizonCull = helpers.applyHorizonCull;
 export const buildSelectedFireCard = helpers.buildSelectedFireCard;
 export const buildFireCard = helpers.buildFireCard;
 export const buildCellCard = helpers.buildCellCard;
diff --git a/src/data/firmsHorizonCull.test.mjs b/src/data/firmsHorizonCull.test.mjs
index 277e4f483..105d2eb20 100644
--- a/src/data/firmsHorizonCull.test.mjs
+++ b/src/data/firmsHorizonCull.test.mjs
@@ -1,11 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import * as Cesium from 'cesium';
-import {
-  applyHorizonCull,
-  createFirmsHeatmapLayer,
-  fireCullPosition,
-} from './firmsHeatmap.js';
+import { createFirmsHeatmapLayer, fireCullPosition } from './firmsHeatmap.js';
 import { FIRE_ANCHOR_LIFT_M } from './fireAnchors.js';
 import { FIRMS_AMBIENT_COHORT_LIMIT, FIRMS_OVERLAY_SOURCE_ID } from './firmsLabels.js';
 import {
@@ -15,7 +11,8 @@ import {
 } from './groundFloor.js';
 import { unregisterSpriteCollection } from './spriteOrder.js';
 import { isOverlayPointVisible, normalizeOverlayEntry } from '../overlays/worldOverlay.js';
-import { mirrorBillboard } from './billboardMirror.js';
+import { createIconSet, ICON_CULL_LIFT } from './iconSet.js';
+import { writeHoldSegment } from './iconSegment.js';
 
 const AUSTIN = { lon: -97.7, lat: 30.2 };
 /** Antipode of Austin — as far behind the limb as a point on Earth can be. */
@@ -29,24 +26,26 @@ const REPRO_HEIGHT_M = 1_500_000;
  * at −22 m but visible at +5/+12 m. Measured against Cesium's own occluder.
  */
 const LIMB_DLON = 41.87;
+/** Farther east, where 11 m reads hidden and 12 m visible from the same camera. */
+const LIFT_BAND_DLON = 41.9452;
 
 /**
- * Billboard stub that records every write to `show` so the tests can assert
- * the pass does not dirty the collection's vertex buffer needlessly.
+ * Whether the icon set's GPU pass draws `row` from `occluder`'s camera: the
+ * shader's horizon test on the row's cull point (its CPU twin).
  */
-function billboard(position, show = true) {
-  return mirrorBillboard({
-    position,
-    _show: show,
-    writes: 0,
-    get show() { return this._show; },
-    set show(value) { this._show = value; this.writes += 1; },
-  });
+function gpuShows(set, row, occluder) {
+  const position = set.position(row, 0, new Cesium.Cartesian3());
+  return set.shown(row) && occluder.isPointVisible(set.cullPoint(row, position));
 }
 
-/** Cesium BillboardCollection-shaped stub. */
-function collection(items) {
-  return { length: items.length, get: (i) => items[i] };
+/** A fire-shaped row (shown, CULL_LIFT) held at `position`. */
+function fireRow(set, id, position) {
+  const row = set.add(id, { layer: 'firms', id });
+  set.setFlag(row, ICON_CULL_LIFT, true);
+  set.setShown(row, true);
+  writeHoldSegment(set.segments, row, position, 0);
+  set.segmentWritten(row);
+  return row;
 }
 
 /** Horizon occluder for a camera directly above Austin at `heightM`. */
@@ -58,92 +57,71 @@ function occluderOverAustin(heightM) {
 }
 
 // ---------------------------------------------------------------------------
-// The pure cull predicate
+// The GPU horizon cull a fire row gets
 // ---------------------------------------------------------------------------
 
-test('applyHorizonCull: far-side fires are hidden, near-side fires stay visible', () => {
+test('icon cull: far-side fires are hidden, near-side fires stay visible', () => {
   const occluder = occluderOverAustin(REPRO_HEIGHT_M);
-  const near = billboard(Cesium.Cartesian3.fromDegrees(AUSTIN.lon, AUSTIN.lat, 0));
-  const nearby = billboard(Cesium.Cartesian3.fromDegrees(AUSTIN.lon + 6, AUSTIN.lat + 4, 0));
-  const far = billboard(Cesium.Cartesian3.fromDegrees(ANTIPODE.lon, ANTIPODE.lat, 0));
-  const otherSide = billboard(Cesium.Cartesian3.fromDegrees(TOKYO.lon, TOKYO.lat, 0));
+  const set = createIconSet();
+  const at = (p) => Cesium.Cartesian3.fromDegrees(p.lon, p.lat, 0);
+  const near = fireRow(set, 'near', at(AUSTIN));
+  const nearby = fireRow(set, 'nearby', at({ lon: AUSTIN.lon + 6, lat: AUSTIN.lat + 4 }));
+  const far = fireRow(set, 'far', at(ANTIPODE));
+  const otherSide = fireRow(set, 'tokyo', at(TOKYO));
 
-  const visible = applyHorizonCull(collection([near, nearby, far, otherSide]), occluder);
-
-  assert.equal(near.show, true, 'the fire under the camera renders');
-  assert.equal(nearby.show, true, 'a fire well inside the horizon renders');
-  assert.equal(far.show, false, 'the antipodal fire must not shine through the planet');
-  assert.equal(otherSide.show, false, 'Tokyo is beyond the limb from Austin at 1.5 Mm');
-  assert.equal(visible, 2, 'returns the surviving count');
+  assert.equal(gpuShows(set, near, occluder), true, 'the fire under the camera renders');
+  assert.equal(gpuShows(set, nearby, occluder), true, 'a fire well inside the horizon renders');
+  assert.equal(gpuShows(set, far, occluder), false, 'the antipodal fire must not shine through the planet');
+  assert.equal(gpuShows(set, otherSide, occluder), false, 'Tokyo is beyond the limb from Austin at 1.5 Mm');
 });
 
-test('applyHorizonCull: raising the camera reveals fires the low camera hid', () => {
-  const paris = () => billboard(Cesium.Cartesian3.fromDegrees(2.35, 48.86, 0));
-
-  const low = paris();
-  applyHorizonCull(collection([low]), occluderOverAustin(REPRO_HEIGHT_M));
-  assert.equal(low.show, false, 'Paris is over the horizon from a 1.5 Mm Austin camera');
-
-  const high = paris();
-  applyHorizonCull(collection([high]), occluderOverAustin(35_000_000));
-  assert.equal(high.show, true, 'from geostationary height the same fire is in view');
+test('icon cull: raising the camera reveals fires the low camera hid', () => {
+  const set = createIconSet();
+  const paris = fireRow(set, 'paris', Cesium.Cartesian3.fromDegrees(2.35, 48.86, 0));
+  assert.equal(gpuShows(set, paris, occluderOverAustin(REPRO_HEIGHT_M)), false);
+  assert.equal(gpuShows(set, paris, occluderOverAustin(35_000_000)), true, 'in view from geostationary height');
 });
 
-test('applyHorizonCull: a hidden fire is restored when it swings back into view', () => {
-  const revealed = billboard(Cesium.Cartesian3.fromDegrees(AUSTIN.lon, AUSTIN.lat, 0), false);
-  applyHorizonCull(collection([revealed]), occluderOverAustin(REPRO_HEIGHT_M));
-  assert.equal(revealed.show, true, 'the cull un-hides as well as hides');
-  assert.equal(revealed.writes, 1);
-});
-
-test('applyHorizonCull: only flipped billboards are written (vertex-buffer churn)', () => {
+test('icon cull: a sub-ellipsoid anchor is judged lifted, a far-side one still culls', () => {
   const occluder = occluderOverAustin(REPRO_HEIGHT_M);
-  const stays = billboard(Cesium.Cartesian3.fromDegrees(AUSTIN.lon, AUSTIN.lat, 0), true);
-  const flips = billboard(Cesium.Cartesian3.fromDegrees(ANTIPODE.lon, ANTIPODE.lat, 0), true);
+  const set = createIconSet();
+  const sunken = fireRow(set, 'sunken', Cesium.Cartesian3.fromDegrees(AUSTIN.lon + LIMB_DLON, AUSTIN.lat, -22));
+  assert.equal(gpuShows(set, sunken, occluder), true, 'the lifted cull point keeps the near-limb fire on screen');
+  set.setFlag(sunken, ICON_CULL_LIFT, false);
+  assert.equal(gpuShows(set, sunken, occluder), false, 'baseline: the raw anchor false-hides at the limb');
 
-  applyHorizonCull(collection([stays, flips]), occluder);
-  applyHorizonCull(collection([stays, flips]), occluder);
-
-  assert.equal(stays.writes, 0, 'an already-visible billboard is never re-assigned');
-  assert.equal(flips.writes, 1, 'a hidden billboard is written once, not once per pass');
+  const far = fireRow(set, 'far', Cesium.Cartesian3.fromDegrees(ANTIPODE.lon, ANTIPODE.lat, -22));
+  assert.equal(gpuShows(set, far, occluder), false, '12 m of lift must not defeat the actual horizon cull');
 });
 
-test('applyHorizonCull: missing collection/occluder/holes are no-ops, not throws', () => {
-  assert.equal(applyHorizonCull(null, occluderOverAustin(REPRO_HEIGHT_M)), 0);
-  assert.equal(applyHorizonCull({ length: 3 }, occluderOverAustin(REPRO_HEIGHT_M)), 0, 'non-collection shape');
-  const item = billboard(Cesium.Cartesian3.fromDegrees(AUSTIN.lon, AUSTIN.lat, 0));
-  assert.equal(applyHorizonCull(collection([item]), null), 0, 'no occluder → leave the layer alone');
-  assert.equal(applyHorizonCull(collection([item]), {}), 0, 'occluder without isPointVisible');
-  assert.equal(item.writes, 0, 'a skipped pass must not touch show');
-  assert.equal(
-    applyHorizonCull(collection([undefined, item]), occluderOverAustin(REPRO_HEIGHT_M)),
-    1,
-    'sparse slots are skipped, surviving neighbours still counted',
-  );
-});
-
-// ---------------------------------------------------------------------------
-// Sub-ellipsoid anchors: datum-correct render point, lifted CULL point
-// ---------------------------------------------------------------------------
-
-test('applyHorizonCull: an index-aligned cull position overrides the render anchor', () => {
+test('fireCullPosition: a card is judged where its sprite is', () => {
   const occluder = occluderOverAustin(REPRO_HEIGHT_M);
-  const sunken = billboard(Cesium.Cartesian3.fromDegrees(AUSTIN.lon + LIMB_DLON, AUSTIN.lat, -22));
-  const lifted = Cesium.Cartesian3.fromDegrees(AUSTIN.lon + LIMB_DLON, AUSTIN.lat, 12);
-
-  applyHorizonCull(collection([sunken]), occluder);
-  assert.equal(sunken.show, false, 'baseline: the raw sub-ellipsoid anchor false-hides at the limb');
-
-  applyHorizonCull(collection([sunken]), occluder, [lifted]);
-  assert.equal(sunken.show, true, 'the lifted cull point keeps the near-limb fire on screen');
-});
-
-test('applyHorizonCull: a lifted cull point does NOT resurrect a genuinely far-side fire', () => {
-  const occluder = occluderOverAustin(REPRO_HEIGHT_M);
-  const far = billboard(Cesium.Cartesian3.fromDegrees(ANTIPODE.lon, ANTIPODE.lat, -22));
-  const lifted = Cesium.Cartesian3.fromDegrees(ANTIPODE.lon, ANTIPODE.lat, 12);
-  applyHorizonCull(collection([far]), occluder, [lifted]);
-  assert.equal(far.show, false, '12 m of lift must not defeat the actual horizon cull');
+  const set = createIconSet();
+  setMeshFloorPreferred(true);
+  try {
+    // Sunk, an 11 m anchor (floor 6 + lift), and well above: each card must
+    // agree with the GPU test on its own row, at limb points where they can.
+    for (const [i, floor] of [-27, 6, 900].entries()) {
+      _clearMeshFloorCellsForTest(); // a reported cell latches its first floor
+      for (const dLon of [LIMB_DLON, LIFT_BAND_DLON]) {
+        const lat = AUSTIN.lat;
+        const lon = AUSTIN.lon + dLon;
+        reportMeshFloorCell(lat, lon, floor);
+        const fire = { index: i, lat, lon, frp: 10, position: null };
+        const cull = fireCullPosition(fire);
+        assert.equal(fire.positionHeight, floor + FIRE_ANCHOR_LIFT_M);
+        const row = fireRow(set, `${floor}:${dLon}`, fire.position);
+        assert.equal(
+          occluder.isPointVisible(cull),
+          gpuShows(set, row, occluder),
+          `floor ${floor} m at +${dLon}°`,
+        );
+      }
+    }
+  } finally {
+    _clearMeshFloorCellsForTest();
+    setMeshFloorPreferred(false);
+  }
 });
 
 test('fireCullPosition: negative-geoid anchor renders at the datum but culls lifted', () => {
@@ -305,17 +283,21 @@ class MockEvent {
   emit() { for (const listener of [...this.listeners]) listener(); }
 }
 
-/** Canvas stub good enough for the pre-baked glow sprites. */
+/**
+ * Canvas stub good enough for the pre-baked glow sprites. Its data URL names
+ * the gradient's colours, so each colour stop gets its own atlas slot.
+ */
 function canvasStub() {
+  const stops = [];
   return {
     width: 0,
     height: 0,
     getContext: () => ({
-      createRadialGradient: () => ({ addColorStop() {} }),
+      createRadialGradient: () => ({ addColorStop: (offset, color) => stops.push(color) }),
       fillStyle: null,
       fillRect() {},
     }),
-    toDataURL: () => 'data:image/png;base64,iVBORw0KGgo=',
+    toDataURL: () => `data:image/png;base64,iVBORw0KGgo=#${stops.join('|')}`,
   };
 }
 
@@ -336,9 +318,8 @@ function rawFire(lat, lon, frp) {
 }
 
 /**
- * Boots the REAL layer against a headless viewer stub with a REAL
- * Cesium.BillboardCollection, so the production hooks (not just the pure
- * predicate) are what the assertions exercise.
+ * Boots the REAL layer against a headless viewer stub; what the GPU would draw
+ * is read off the layer's real icon set (`gpuShows`) from the stub camera.
  */
 function createHarness(rawFires) {
   const originalFetch = globalThis.fetch;
@@ -384,7 +365,13 @@ function createHarness(rawFires) {
       preRender,
       primitives: {
         add: (value) => { primitives.push(value); return value; },
-        remove: () => {},
+        remove: (value) => {
+          const at = primitives.indexOf(value);
+          if (at < 0) return false;
+          primitives.splice(at, 1);
+          value.destroy();
+          return true;
+        },
         contains: () => false,
       },
       frameState: { mode: Cesium.SceneMode.SCENE3D, mapProjection: new Cesium.GeographicProjection() },
@@ -408,15 +395,19 @@ function createHarness(rawFires) {
     viewer,
     preRender,
     moveEnd,
-    /** The real BillboardCollection the layer created. */
-    billboards: () => primitives[0],
+    /** The icon set the layer draws its detections from. */
+    icons: () => primitives[0].set,
+    /** Primitives currently in the stub scene. */
+    primitives,
     /** Latest entry list published to the overlay host. */
     latestEntries: () => entryCalls[entryCalls.length - 1] || [],
-    /** `show` flags keyed by billboard pick id. */
+    /** Whether the GPU draws each row from the current camera, by pick id. */
     showById() {
-      const bb = primitives[0];
+      const set = primitives[0].set;
+      const occluder = new Cesium.EllipsoidalOccluder(Cesium.Ellipsoid.WGS84, viewer.camera.positionWC);
       const out = new Map();
-      for (let i = 0; i < bb.length; i += 1) out.set(bb.get(i).id, bb.get(i).show);
+      for (let row = 0; row < set.count; row += 1)
+        out.set(set.idAt(row), set.show && gpuShows(set, row, occluder));
       return out;
     },
     moveCameraTo(lon, lat, height = REPRO_HEIGHT_M) {
@@ -434,7 +425,7 @@ function createHarness(rawFires) {
   };
 }
 
-test('layer: a detection rebuild culls its own freshly-added sprites', async () => {
+test('layer: far-side detections are culled from the first frame', async () => {
   const harness = createHarness([
     rawFire(AUSTIN.lat, AUSTIN.lon, 120),
     rawFire(ANTIPODE.lat, ANTIPODE.lon, 900),
@@ -454,7 +445,7 @@ test('layer: a detection rebuild culls its own freshly-added sprites', async ()
   }
 });
 
-test('layer: camera moveEnd re-culls without a rebuild', async () => {
+test('layer: the GPU cull follows the camera with no CPU show pass', async () => {
   const harness = createHarness([
     rawFire(AUSTIN.lat, AUSTIN.lon, 120),
     rawFire(TOKYO.lat, TOKYO.lon, 800),
@@ -467,6 +458,9 @@ test('layer: camera moveEnd re-culls without a rebuild', async () => {
     harness.moveCameraTo(TOKYO.lon, TOKYO.lat);
     harness.moveEnd.emit();
 
+    const set = harness.icons();
+    for (let row = 0; row < set.count; row += 1)
+      assert.equal(set.shown(row), true, `${set.idAt(row)} keeps its row shown; the GPU decides`);
     const show = harness.showById();
     assert.equal(show.get('firms-1'), true, 'Tokyo becomes visible once the camera is over it');
     assert.equal(show.get('firms-0'), false, 'Austin drops behind the limb');
@@ -475,32 +469,33 @@ test('layer: camera moveEnd re-culls without a rebuild', async () => {
   }
 });
 
-test('layer: the throttled preRender watcher re-culls on a camera move', async () => {
-  const harness = createHarness([
-    rawFire(AUSTIN.lat, AUSTIN.lon, 120),
-    rawFire(TOKYO.lat, TOKYO.lon, 800),
-  ]);
+test('layer: a refresh keeps rows and restyles one whose index now holds another fire', async () => {
+  const fires = [rawFire(AUSTIN.lat, AUSTIN.lon, 400), rawFire(TOKYO.lat, TOKYO.lon, 800)];
+  const harness = createHarness(fires);
   try {
     harness.layer.init(harness.viewer);
     await harness.layer.enable(harness.viewer);
-    harness.moveCameraTo(TOKYO.lon, TOKYO.lat);
-    // The watcher is throttled to LOD_CHECK_MS (650 ms) against
-    // performance.now(), whose value at this point depends on process
-    // start-up — so emit, wait out the full throttle window, and emit again.
-    // Whichever tick passes the gate, one of them must run the pass.
-    harness.preRender.emit();
-    await new Promise((resolve) => { setTimeout(resolve, 700); });
-    harness.preRender.emit();
+    const set = harness.icons();
+    const austin = set.row('firms-0');
+    const handle = set.handleAt(austin);
+    const before = set.width(austin);
+    const beforeImage = set.imageFar(austin);
 
-    const show = harness.showById();
-    assert.equal(show.get('firms-1'), true, 'Tokyo revealed by the preRender pass');
-    assert.equal(show.get('firms-0'), false, 'Austin culled by the preRender pass');
+    fires[0] = rawFire(AUSTIN.lat + 0.5, AUSTIN.lon, 1);
+    await harness.layer.update();
+
+    const row = set.row('firms-0');
+    assert.equal(set.handleAt(row), handle, 'the row (and its pick id) survives the rebuild');
+    assert.ok(set.width(row) < before, `restyled for the weaker fire: ${set.width(row)} < ${before}`);
+    assert.notEqual(set.imageFar(row), beforeImage, 'a red glow becomes a yellow one');
+    const carto = Cesium.Cartographic.fromCartesian(set.position(row, 0, new Cesium.Cartesian3()));
+    assert.ok(Math.abs(Cesium.Math.toDegrees(carto.latitude) - (AUSTIN.lat + 0.5)) < 1e-6, 'moved to the new fire');
   } finally {
     harness.cleanup();
   }
 });
 
-test('layer: re-enabling after the camera moved does not expose stale far-side sprites', async () => {
+test('layer: re-enabling after the camera moved shows the icons, culled from the new camera', async () => {
   const harness = createHarness([
     rawFire(AUSTIN.lat, AUSTIN.lon, 120),
     rawFire(TOKYO.lat, TOKYO.lon, 800),
@@ -517,10 +512,10 @@ test('layer: re-enabling after the camera moved does not expose stale far-side s
     await harness.layer.enable(harness.viewer);
 
     // Assert with NO camera event fired and NO refetch (fires are already
-    // loaded, so enable() does not reload): the enable path itself must have
-    // re-culled before the collection went visible.
+    // loaded, so enable() does not reload): the GPU culls from the current
+    // camera on the first frame.
     const show = harness.showById();
-    assert.equal(harness.billboards().show, true, 'the collection is visible again');
+    assert.equal(harness.icons().show, true, 'the icon set is visible again');
     assert.equal(show.get('firms-1'), true, 'the Tokyo fire is revealed at enable time');
     assert.equal(show.get('firms-0'), false, 'the Austin fire is NOT left shining through the planet');
   } finally {
@@ -528,6 +523,47 @@ test('layer: re-enabling after the camera moved does not expose stale far-side s
   }
 });
 
+test('layer: a refresh drops rows whose fires left, and an empty one drops them all', async () => {
+  const fires = [
+    rawFire(AUSTIN.lat, AUSTIN.lon, 120),
+    rawFire(AUSTIN.lat + 1, AUSTIN.lon, 300),
+    rawFire(AUSTIN.lat + 2, AUSTIN.lon, 200),
+  ];
+  const harness = createHarness(fires);
+  try {
+    harness.layer.init(harness.viewer);
+    await harness.layer.enable(harness.viewer);
+    const set = harness.icons();
+    assert.equal(set.count, 3);
+
+    // Index 0 still holds a fire; 1 and 2 are gone, so their rows swap out.
+    fires.splice(1, 2);
+    await harness.layer.update();
+    assert.deepEqual(
+      Array.from({ length: set.count }, (_, row) => set.idAt(row)),
+      ['firms-0'],
+    );
+    assert.equal(set.metaAt(set.row('firms-0')).fire.lat, AUSTIN.lat, 'the kept row holds its own fire');
+
+    fires.length = 0;
+    await harness.layer.update();
+    assert.equal(set.count, 0, 'an empty refresh leaves no sprite behind');
+    assert.equal(harness.latestEntries().length, 0, 'nor any card');
+  } finally {
+    harness.cleanup();
+  }
+});
+
+test('layer: destroy takes the icons out of the scene', async () => {
+  const harness = createHarness([rawFire(AUSTIN.lat, AUSTIN.lon, 120)]);
+  harness.layer.init(harness.viewer);
+  await harness.layer.enable(harness.viewer);
+  const primitive = harness.primitives[0];
+  harness.cleanup();
+  assert.equal(harness.primitives.includes(primitive), false);
+  assert.equal(primitive.isDestroyed(), true);
+});
+
 test('layer: a near-limb fire on a sub-ellipsoid anchor is not culled by its datum', async () => {
   const lat = AUSTIN.lat;
   const lon = AUSTIN.lon + LIMB_DLON;
@@ -543,14 +579,14 @@ test('layer: a near-limb fire on a sub-ellipsoid anchor is not culled by its dat
     harness.layer.init(harness.viewer);
     await harness.layer.enable(harness.viewer);
 
-    const bb = harness.billboards();
-    const sunken = bb.get(1);
-    const carto = Cesium.Cartographic.fromCartesian(sunken.position);
+    const set = harness.icons();
+    const sunken = set.row('firms-1');
+    const carto = Cesium.Cartographic.fromCartesian(set.position(sunken, 0, new Cesium.Cartesian3()));
     assert.ok(
       Math.abs(carto.height - (-27 + FIRE_ANCHOR_LIFT_M)) < 0.5,
       `the sprite still RENDERS at the datum-correct anchor, got ${carto.height}`,
     );
-    assert.equal(sunken.show, true, 'the near-limb fire stays on screen (lifted cull anchor)');
+    assert.equal(harness.showById().get('firms-1'), true, 'the near-limb fire stays on screen (lifted cull anchor)');
     assert.equal(harness.showById().get('firms-0'), true, 'the camera-nadir fire is unaffected');
   } finally {
     harness.cleanup();
diff --git a/src/data/spriteOrder.test.mjs b/src/data/spriteOrder.test.mjs
index e5ea59d6c..38e1d02c3 100644
--- a/src/data/spriteOrder.test.mjs
+++ b/src/data/spriteOrder.test.mjs
@@ -115,7 +115,7 @@ test('flights, AIS, and FIRMS enable paths are wired through the shared sprite r
   assert.match(firmsLayer.enable.toString(), /restoreSpriteOrderOnEnable\('firms', viewer\)/);
   assert.match(
     createFirmsRendering.toString(),
-    /registerSpriteCollection\('firms', layerState\._billboards\);\s*restoreSpriteOrder\(layerState\._viewer\);/,
+    /registerSpriteCollection\('firms', layerState\._iconPrimitive\);\s*restoreSpriteOrder\(layerState\._viewer\);/,
     'lazy FIRMS registration must restore order immediately',
   );
 });
diff --git a/src/layers/firms/lifecycle.js b/src/layers/firms/lifecycle.js
index 7e0b42a00..2b5740335 100644
--- a/src/layers/firms/lifecycle.js
+++ b/src/layers/firms/lifecycle.js
@@ -28,17 +28,9 @@ export function createLifecycle({
       layerState._viewer = viewer;
       if (!layerState._dataSource) this.init(viewer);
       if (layerState._dataSource) layerState._dataSource.show = true;
-      if (layerState._billboards) {
-        // The camera can have moved anywhere while the layer was off: moveEnd
-        // was not being listened to, and the preRender watcher is inert while
-        // disabled AND while the (untimed) refetch below is in flight. So the
-        // retained per-sprite show flags describe the OLD viewpoint. Re-cull
-        // BEFORE the collection becomes visible — otherwise re-enabling at a
-        // new location flashes far-side fires through the planet (and keeps
-        // near-side ones hidden) until the fetch resolves.
-        components.rendering.refreshHorizonCulling();
-        layerState._billboards.show = true;
-      }
+      // The GPU culls the far side each frame, so retained rows are right
+      // for wherever the camera went while the layer was off.
+      if (layerState._icons) layerState._icons.show = true;
       overlayHost.setVisible(FIRMS_OVERLAY_SOURCE_ID, true);
       components.viewport.installLodWatcher();
       components.viewport.installMoveEndWatcher();
@@ -63,7 +55,7 @@ export function createLifecycle({
       layerState._enabled = false;
       components.selection.clearFireSelection();
       if (layerState._dataSource) layerState._dataSource.show = false;
-      if (layerState._billboards) layerState._billboards.show = false;
+      if (layerState._icons) layerState._icons.show = false;
       overlayHost.clearSource(FIRMS_OVERLAY_SOURCE_ID);
       overlayHost.setVisible(FIRMS_OVERLAY_SOURCE_ID, false);
       clearSelectedEntityContextForLayer(id);
@@ -110,7 +102,6 @@ export function createLifecycle({
       layerState._labelLodDistance = 0;
       layerState._pickIndexById.clear();
       layerState._fireByCardId.clear();
-      layerState._cullPositions.length = 0;
       layerState._camSnapValid = false;
     },
   };
diff --git a/src/layers/firms/model.js b/src/layers/firms/model.js
index 1c5873812..a6fc1028e 100644
--- a/src/layers/firms/model.js
+++ b/src/layers/firms/model.js
@@ -9,11 +9,10 @@ import {
 import {
   VIEW_PADDING,
   DETECTION_COLOR_STOPS,
-  CULL_LIFT_THRESHOLD_M,
-  CULL_LIFT_M,
+  GLOW_SPRITE_PX,
   LABEL_MIN_SEP_PX,
 } from './policy.js';
-import { billboardState, setBillboard } from '../../data/billboardMirror.js';
+import { ICON_CULL_HEIGHT_M } from '../../data/iconSet.js';
 
 export function createModel({
   layerState,
@@ -161,18 +160,17 @@ export function createModel({
   /**
    * Build (and cache) a radial-glow sprite: hot near-white center fading
    * through the stop color to a transparent edge. The glow lives in the
-   * sprite itself because global bloom defaults OFF.
+   * sprite itself because global bloom defaults OFF. One raster per color
+   * (GLOW_SPRITE_PX); each fire draws it at its own size.
    * @param {{name: string, color: Cesium.Color}} stop - Color stop.
-   * @param {number} corePx - Bucketed core size in pixels.
    * @returns {string} PNG data URL.
    */
 
-  function glowSprite(stop, corePx) {
-    const key = `${stop.name}:${corePx}`;
-    const cached = layerState.glowSpriteCache.get(key);
+  function glowSprite(stop) {
+    const cached = layerState.glowSpriteCache.get(stop.name);
     if (cached) return cached;
 
-    const dimension = corePx * 2;
+    const dimension = GLOW_SPRITE_PX;
     const canvas = document.createElement('canvas');
     canvas.width = dimension;
     canvas.height = dimension;
@@ -200,7 +198,7 @@ export function createModel({
     context.fillRect(0, 0, dimension, dimension);
 
     const dataUrl = canvas.toDataURL('image/png');
-    layerState.glowSpriteCache.set(key, dataUrl);
+    layerState.glowSpriteCache.set(stop.name, dataUrl);
     return dataUrl;
   }
 
@@ -231,21 +229,25 @@ export function createModel({
   /**
    * Occlusion-test anchor for one detection. Returns the render position
    * outright for anchors comfortably above the ellipsoid (the common case) and
-   * a lazily-cached lifted point otherwise — see CULL_LIFT_THRESHOLD_M. This
-   * NEVER feeds rendering: the datum-correct anchor from {@link firePosition}
-   * is what the sprite and the card are drawn at.
+   * a lazily-cached lifted point otherwise, the point the icon set's GPU
+   * horizon test judges a fire row at (ICON_CULL_LIFT), so a card shows exactly
+   * when its sprite does. In negative-geoid coastal regions the floored anchor
+   * lands tens of metres BELOW the WGS84 ellipsoid, which the occluder judges
+   * beyond the horizon while true-surface neighbours stay visible. This NEVER
+   * feeds rendering: the datum-correct anchor from {@link firePosition} is what
+   * the sprite and the card are drawn at.
    * @param {Object} fire - Detection record.
    * @returns {Cesium.Cartesian3}
    */
 
   function fireCullPosition(fire) {
     const position = firePosition(fire);
-    if (fire.positionHeight >= CULL_LIFT_THRESHOLD_M) return position;
+    if (fire.positionHeight >= ICON_CULL_HEIGHT_M) return position;
     if (!fire.cullPosition) {
       fire.cullPosition = Cesium.Cartesian3.fromDegrees(
         fire.lon,
         fire.lat,
-        CULL_LIFT_M,
+        ICON_CULL_HEIGHT_M,
       );
     }
     return fire.cullPosition;
@@ -261,48 +263,7 @@ export function createModel({
    */
 
   function cellCullPosition(lon, lat) {
-    return Cesium.Cartesian3.fromDegrees(lon, lat, CULL_LIFT_M);
-  }
-
-  /**
-   * Horizon-cull a billboard collection against an ellipsoid occluder.
-   *
-   * The Cesium globe is hidden in this app (Google 3D Tiles render the planet),
-   * so nothing writes far-side depth — and these sprites are additionally
-   * always-on-top (`disableDepthTestDistance: INFINITY`, so a detection is never
-   * swallowed by terrain it sits on). Without an explicit occluder pass, fires on
-   * the opposite side of the Earth shine through the planet at tilted mid-altitude
-   * views. Same pattern as the flights/CCTV layers' `EllipsoidalOccluder` passes.
-   *
-   * Pure and allocation-free: reads the billboard's mirrored position and show,
-   * and writes `show` only when it actually flips (assigning `show` dirties the
-   * collection's vertex buffer). Accepts any `{length, get(i)}` shape so it is unit-testable without
-   * a WebGL scene.
-   *
-   * @param {?{length: number, get: function(number): (Object|undefined)}} billboards
-   *   Billboard collection (or collection-shaped stub).
-   * @param {?{isPointVisible: function(Object): boolean}} occluder Horizon occluder.
-   * @param {?Array<Cesium.Cartesian3>} [cullPositions=null] Index-aligned lifted
-   *   occlusion-test anchors (see {@link fireCullPosition}); falls back to the
-   *   billboard's own render position wherever an entry is absent.
-   * @returns {number} Count of billboards left visible (0 when nothing to test).
-   */
-
-  function applyHorizonCull(billboards, occluder, cullPositions = null) {
-    if (!billboards || typeof billboards.get !== 'function') return 0;
-    if (typeof occluder?.isPointVisible !== 'function') return 0;
-    const total = Number(billboards.length) || 0;
-    let visibleCount = 0;
-    for (let i = 0; i < total; i += 1) {
-      const billboard = billboards.get(i);
-      if (!billboard) continue;
-      const pushed = billboardState(billboard);
-      const point = (cullPositions && cullPositions[i]) || pushed.position;
-      const visible = occluder.isPointVisible(point) === true;
-      if (pushed.show !== visible) setBillboard(billboard, 'show', visible);
-      if (visible) visibleCount += 1;
-    }
-    return visibleCount;
+    return Cesium.Cartesian3.fromDegrees(lon, lat, ICON_CULL_HEIGHT_M);
   }
 
   /**
@@ -589,7 +550,6 @@ export function createModel({
     firePosition,
     fireCullPosition,
     cellCullPosition,
-    applyHorizonCull,
     screenSeparated,
     buildSelectedFireCard,
     buildFireCard,
diff --git a/src/layers/firms/policy.js b/src/layers/firms/policy.js
index 673aab871..72ecf2db1 100644
--- a/src/layers/firms/policy.js
+++ b/src/layers/firms/policy.js
@@ -8,7 +8,7 @@ export const REFRESH_INTERVAL_MS = 600_000;
 /**
  * LOD bands keyed by camera height. `cells` bands render aggregated
  * ground-clamped heat rectangles; `detections` bands (< ~750km plus the
- * local band) render individual fire detections as glow-sprite billboards.
+ * local band) render individual fire detections as glow-sprite icons.
  * Labels in every band go through the shared screen-space greedy declutter
  * (hard cap MAX_AMBIENT_LABELS) — there are no per-band label knobs.
  */
@@ -73,20 +73,12 @@ export const LABEL_MIN_SEP_PX = 150;
 export const LABEL_VIEW_MARGIN_PX = 16;
 
 /**
- * Anchors below this height get a separate LIFTED point for occlusion tests
- * (never for rendering). Mirrors the flights layer's `cullPosition` idiom
- * (`renderAltitudeM < 10` → test at 12 m): `fireAnchorHeight` is ground floor
- * + lift, and in negative-geoid coastal regions that lands a few tens of
- * metres BELOW the WGS84 ellipsoid — EllipsoidalOccluder then judges such a
- * point "beyond the horizon" while its true-surface neighbours stay visible,
- * so near-limb fires would blink out for a datum reason.
+ * Glow sprites are rasterised once per colour at the largest core size
+ * (frpPixelSize tops out at 28 px, a 56 px sprite) and drawn smaller per fire:
+ * the gradient stops are relative, so the glow keeps its shape at any size.
  */
 
-export const CULL_LIFT_THRESHOLD_M = 10;
-
-/** Height of the lifted occlusion-test point (flights uses the same 12 m). */
-
-export const CULL_LIFT_M = 12;
+export const GLOW_SPRITE_PX = 56;
 
 /** Color stops shared by cell heat fills and detection glow sprites. */
 
diff --git a/src/layers/firms/rendering.js b/src/layers/firms/rendering.js
index 1a8652f0e..34257718e 100644
--- a/src/layers/firms/rendering.js
+++ b/src/layers/firms/rendering.js
@@ -1,8 +1,11 @@
 import * as Cesium from 'cesium';
 import { FIRMS_OVERLAY_SOURCE_ID } from '../../data/firmsLabels.js';
 import { horizonOccluder } from '../../data/iconOrientation.js';
-import { LOD_LEVELS, CONTEXT_TOP_N } from './policy.js';
-import { addBillboard } from '../../data/billboardMirror.js';
+import { LOD_LEVELS, CONTEXT_TOP_N, GLOW_SPRITE_PX } from './policy.js';
+import { createIconSet, ICON_CULL_LIFT } from '../../data/iconSet.js';
+import { writeHoldSegment } from '../../data/iconSegment.js';
+import { IconSetPrimitive } from '../../data/iconSetPrimitive.js';
+import { iconAtlas } from '../../data/iconAtlas.js';
 
 export function createRendering({
   layerState,
@@ -20,18 +23,18 @@ export function createRendering({
    * when neither the (hysteresis-damped) LOD band nor the padded view
    * rectangle changed meaningfully.
    * @param {boolean} force - Rebuild even if LOD/view appear unchanged.
-   * @returns {boolean} True when a rebuild actually ran. Callers use this to
-   *   avoid a second horizon walk in the same tick: a rebuild already culls
-   *   its freshly-added sprites, an early-out does not.
+   * @returns {boolean} True when a rebuild actually ran.
    */
 
   function renderCurrentLod(force = false) {
-    if (
-      !layerState._dataSource ||
-      !layerState._fires.length ||
-      !layerState._viewer
-    )
+    if (!layerState._dataSource || !layerState._viewer) return false;
+    if (!layerState._fires.length) {
+      // A refresh that came back empty takes down what the last one drew, so
+      // no sprite or card is left on screen (and clickable) for a fire that is
+      // gone.
+      if (force) clearRendered();
       return false;
+    }
     const lodIndex = components.viewport.selectLodIndex(
       components.viewport.cameraHeight(),
     );
@@ -60,6 +63,16 @@ export function createRendering({
     return true;
   }
 
+  function clearRendered() {
+    layerState._dataSource.entities.removeAll();
+    layerState._icons?.clear();
+    layerState._pickIndexById.clear();
+    layerState._cellCount = 0;
+    layerState._labelCandidates = [];
+    components.cards.rebuildAmbientLabels();
+    components.selection.refreshContextRegistrations([]);
+  }
+
   /**
    * Bin all detections into grid cells, then viewport-clip BEFORE the
    * top-N cap so fires in view never lose their slot to higher-scoring
@@ -132,9 +145,8 @@ export function createRendering({
   function renderCells(cells, lod, bounds) {
     ensureDetectionCollections();
     layerState._dataSource.entities.removeAll();
-    if (layerState._billboards) layerState._billboards.removeAll();
+    layerState._icons?.clear();
     layerState._pickIndexById.clear();
-    layerState._cullPositions.length = 0;
     layerState._cellCount = cells.length;
     const maxScore = Math.max(1, ...cells.map(components.model.heatScore));
 
@@ -189,7 +201,7 @@ export function createRendering({
 
   /**
    * Render individual detections (local/close bands) as pre-baked
-   * radial-glow sprite billboards sized by FRP, capped per viewport by
+   * radial-glow sprite icons sized by FRP, capped per viewport by
    * highest FRP, depth test disabled. The 3D Tiles mesh is never sampled
    * per point; instead, the CLOSE band (where terrain parallax is actually
    * visible) batch-warms the shared cached DEM floor for its rendered
@@ -205,10 +217,9 @@ export function createRendering({
   function renderDetections(lod, bounds) {
     ensureDetectionCollections();
     layerState._dataSource.entities.removeAll();
-    if (!layerState._billboards) return;
-    layerState._billboards.removeAll();
+    const set = layerState._icons;
+    if (!set) return;
     layerState._pickIndexById.clear();
-    layerState._cullPositions.length = 0;
 
     let candidates;
     if (bounds) {
@@ -231,41 +242,28 @@ export function createRendering({
     layerState._labelCandidates = [];
     layerState._labelLodDistance = lod.labelDistance;
 
+    // Fires keep their rows across rebuilds: a pan that keeps a fire in view
+    // rewrites nothing for it, and only rows that left the view go.
+    const keep = new Set();
     for (const fire of candidates) {
-      const coreSize = components.model.frpPixelSize(fire.frp);
       const position = components.model.firePosition(fire);
-      const cullPosition = components.model.fireCullPosition(fire);
       const pickId = `firms-${fire.index}`;
       layerState._pickIndexById.set(pickId, fire);
-      layerState._cullPositions.push(cullPosition);
-      const corePx = components.model.sizeBucket(coreSize);
-      addBillboard(layerState._billboards, {
-        id: pickId,
-        position,
-        image: components.model.glowSprite(
-          components.model.detectionColorStop(fire),
-          corePx,
-        ),
-        // The glow sprite's own size (see glowSprite), stated for Core's mirror.
-        width: corePx * 2,
-        height: corePx * 2,
-        verticalOrigin: Cesium.VerticalOrigin.CENTER,
-        horizontalOrigin: Cesium.HorizontalOrigin.CENTER,
-        disableDepthTestDistance: Number.POSITIVE_INFINITY,
-      });
+      keep.add(pickId);
+      placeFireIcon(set, pickId, fire, position);
       // FRP-sorted walk: candidate order doubles as label priority.
       layerState._labelCandidates.push({
         position,
-        cullPosition,
+        cullPosition: components.model.fireCullPosition(fire),
         fire,
         cell: null,
       });
     }
+    for (let row = set.count - 1; row >= 0; row -= 1) {
+      const pickId = set.idAt(row);
+      if (!keep.has(pickId)) set.remove(pickId);
+    }
 
-    // Freshly-added sprites default to show=true; cull the far side now so a
-    // rebuild never flashes through-the-planet detections while the camera
-    // sits still (the moveEnd/preRender hooks only fire on camera motion).
-    refreshHorizonCulling();
     components.cards.rebuildAmbientLabels();
     components.selection.refreshContextRegistrations(
       candidates.slice(0, CONTEXT_TOP_N),
@@ -286,30 +284,83 @@ export function createRendering({
     }
   }
 
+  /**
+   * A fire's glow row: drawn depth-test-free at its anchor (a detection is
+   * never swallowed by terrain it sits on), with the far side of the globe
+   * culled on the GPU each frame. The Cesium globe is hidden here (Google 3D
+   * Tiles render the planet), so nothing writes far-side depth, and the cull
+   * is what keeps fires from shining through the planet. The anchor moves
+   * once, when its floor warms.
+   */
+  function placeFireIcon(set, pickId, fire, position) {
+    let row = set.row(pickId);
+    if (row < 0) {
+      row = set.add(pickId, {
+        layer: 'firms',
+        id: pickId,
+        fire: null,
+        position: null,
+      });
+      set.setFlag(row, ICON_CULL_LIFT, true);
+      set.setShown(row, true);
+    }
+    const meta = set.metaAt(row);
+    // A refresh reuses indices, so a kept row can hold a different detection.
+    if (meta.fire !== fire) {
+      meta.fire = fire;
+      const slot = iconAtlas.slot(
+        components.model.glowSprite(components.model.detectionColorStop(fire)),
+        GLOW_SPRITE_PX,
+      );
+      const corePx = components.model.sizeBucket(
+        components.model.frpPixelSize(fire.frp),
+      );
+      set.setImage(row, slot, slot);
+      set.setSize(row, corePx * 2, corePx * 2);
+    }
+    if (meta.position === position) return;
+    meta.position = position;
+    writeHoldSegment(set.segments, row, position, 0);
+    set.segmentWritten(row);
+  }
+
+  /** The scene the icon primitive was added to. */
+  let iconScene = null;
+
   function ensureDetectionCollections() {
-    if (!layerState._viewer || layerState._billboards) return;
-    layerState._billboards = new Cesium.BillboardCollection({
-      scene: layerState._viewer.scene,
-      blendOption: Cesium.BlendOption.TRANSLUCENT,
+    if (!layerState._viewer || layerState._icons) return;
+    const epoch = Cesium.JulianDate.now();
+    layerState._icons = createIconSet({ epoch });
+    layerState._iconPrimitive = new IconSetPrimitive({
+      set: layerState._icons,
+      renderTime: () => epoch,
+      requestRender: () => layerState._viewer?.scene?.requestRender?.(),
     });
-    layerState._billboards.show = layerState._enabled;
-    layerState._viewer.scene.primitives.add(layerState._billboards);
-    registerSpriteCollection('firms', layerState._billboards);
+    layerState._icons.show = layerState._enabled;
+    iconScene = layerState._viewer.scene;
+    iconScene.primitives.add(layerState._iconPrimitive);
+    registerSpriteCollection('firms', layerState._iconPrimitive);
     restoreSpriteOrder(layerState._viewer);
     overlayHost.setVisible(FIRMS_OVERLAY_SOURCE_ID, layerState._enabled);
   }
 
-  function removeDetectionCollections(viewer) {
-    const scene = viewer?.scene || layerState._viewer?.scene;
-    if (scene && !scene.isDestroyed?.()) {
-      try {
-        if (layerState._billboards)
-          scene.primitives.remove(layerState._billboards);
-      } catch {
-        /* already torn down */
-      }
+  /**
+   * Take the icons out of the scene they were added to, whichever viewer the
+   * caller tears down, and free them: a destroyed primitive left in a live
+   * scene throws on its next frame.
+   */
+  function removeDetectionCollections() {
+    const primitive = layerState._iconPrimitive;
+    try {
+      if (primitive && iconScene && !iconScene.isDestroyed?.())
+        iconScene.primitives.remove(primitive);
+    } catch {
+      /* already torn down */
     }
-    layerState._billboards = null;
+    if (primitive && !primitive.isDestroyed()) primitive.destroy();
+    iconScene = null;
+    layerState._iconPrimitive = null;
+    layerState._icons = null;
     overlayHost.clearSource(FIRMS_OVERLAY_SOURCE_ID);
     overlayHost.setVisible(FIRMS_OVERLAY_SOURCE_ID, false);
   }
@@ -331,22 +382,6 @@ export function createRendering({
     return horizonOccluder(camera);
   }
 
-  /**
-   * Hide detection sprites that sit beyond the ellipsoid horizon (see
-   * {@link applyHorizonCull}). Runs on the cadences that already exist in this
-   * layer — the throttled LOD preRender watcher (camera-moved only), camera
-   * moveEnd, and each detection rebuild — never as a new per-frame pass.
-   * No-ops in the `cells` bands, where the collection is empty.
-   */
-
-  function refreshHorizonCulling() {
-    if (!layerState._billboards || !layerState._billboards.length) return;
-    components.model.applyHorizonCull(
-      layerState._billboards,
-      fireHorizonOccluder(),
-      layerState._cullPositions,
-    );
-  }
   return {
     renderCurrentLod,
     aggregateFires,
@@ -355,6 +390,5 @@ export function createRendering({
     ensureDetectionCollections,
     removeDetectionCollections,
     fireHorizonOccluder,
-    refreshHorizonCulling,
   };
 }
diff --git a/src/layers/firms/selection.js b/src/layers/firms/selection.js
index 3ffc33354..fcba3ecbd 100644
--- a/src/layers/firms/selection.js
+++ b/src/layers/firms/selection.js
@@ -88,8 +88,8 @@ export function createSelection({
 
   /**
    * Resolve a scene pick to one of this layer's fire records, or null.
-   * BillboardCollection picks surface our id either on picked.primitive.id
-   * or directly on picked.id depending on the CesiumJS pick path.
+   * Icon-set picks carry our row id on picked.id and on picked.primitive.id;
+   * either is accepted.
    * @param {*} picked - Result of scene.pick().
    * @returns {?Object} Fire record.
    */
diff --git a/src/layers/firms/state.js b/src/layers/firms/state.js
index 48ae11db2..6f13165a8 100644
--- a/src/layers/firms/state.js
+++ b/src/layers/firms/state.js
@@ -3,7 +3,7 @@ import * as Cesium from 'cesium';
 export function createFirmsState({ services, config }) {
   const layerState = {};
 
-  /** Pre-baked radial-glow sprites keyed by `<colorStop>:<sizeBucket>`. */
+  /** Pre-baked radial-glow sprites keyed by color stop name. */
 
   layerState.glowSpriteCache = new Map();
 
@@ -19,7 +19,11 @@ export function createFirmsState({ services, config }) {
 
   layerState._dataSource = null;
 
-  layerState._billboards = null;
+  /** Detection glow rows and the primitive that draws them. */
+
+  layerState._icons = null;
+
+  layerState._iconPrimitive = null;
 
   layerState._enabled = false;
 
@@ -83,16 +87,6 @@ export function createFirmsState({ services, config }) {
 
   layerState._fireByCardId = new Map();
 
-  /**
-   * Occlusion-test anchors index-aligned with the billboard collection (the
-   * collection is cleared and refilled in one ordered pass per rebuild, and
-   * nothing else adds to it). Lifted where the render anchor sits at/below
-   * the ellipsoid — see {@link fireCullPosition}.
-   * @type {Array<Cesium.Cartesian3>}
-   */
-
-  layerState._cullPositions = [];
-
   /**
    * gridDegrees -> heat-sorted full cell list. The full-grid aggregation is
    * viewport-independent but walks every detection (~200k live), so it is
diff --git a/src/layers/firms/viewport.js b/src/layers/firms/viewport.js
index 932fe2e75..5ea2b191a 100644
--- a/src/layers/firms/viewport.js
+++ b/src/layers/firms/viewport.js
@@ -24,13 +24,7 @@ export function createViewport({
     if (layerState._moveEndRemover || !layerState._viewer) return;
     layerState._moveEndRemover =
       layerState._viewer.camera.moveEnd.addEventListener(() => {
-        if (!layerState._enabled) return;
-        // Settled-camera exactness for the horizon pass (the throttled preRender
-        // watcher can last have run up to LOD_CHECK_MS before the camera
-        // stopped). Runs ahead of the `_loading` gate on purpose: the sprites on
-        // screen during a refresh are the ones that need culling.
-        components.rendering.refreshHorizonCulling();
-        if (layerState._loading) return;
+        if (!layerState._enabled || layerState._loading) return;
         components.cards.rebuildAmbientLabels();
       });
   }
@@ -177,18 +171,8 @@ export function createViewport({
         Cesium.Cartesian3.clone(camera.positionWC, layerState._camPos);
         Cesium.Cartesian3.clone(camera.directionWC, layerState._camDir);
         layerState._camSnapValid = true;
-        // The camera moved, so the horizon moved. A rebuild culls its own fresh
-        // sprites (renderDetections); an early-out — same LOD band and view
-        // rect, or a refresh in flight — does not, so cull here instead.
-        // Exactly ONE occlusion walk per tick either way, bounded by the
-        // idle-gate + LOD_CHECK_MS throttle above: a parked camera costs
-        // nothing, a moving one pays one ≤maxDetections show-flip walk at
-        // ~1.5 Hz.
-        const rebuilt =
-          layerState._fires.length && !layerState._loading
-            ? components.rendering.renderCurrentLod(false)
-            : false;
-        if (!rebuilt) components.rendering.refreshHorizonCulling();
+        if (layerState._fires.length && !layerState._loading)
+          components.rendering.renderCurrentLod(false);
       });
   }