Cross-fade Active Fires markers and heatmap; fix the spot size

The far-zoom heatmap now uses the ½× grid (4096 × 2048, ≈10 km per
pixel, one-pixel blur), so a lone fire's spot matches its marker at the
3,000 km hand-off. The spot size slider and its share option are gone.

Markers and heatmap are both kept built at every zoom and cross-fade by
camera height between 2,400 and 3,600 km on every frame, so a fast zoom
never shows a beat with neither. The heatmap fades by imagery alpha:
hiding a Cesium imagery layer unmaps it from the globe tiles, and showing
it again re-mapped them late, which was the gap at the band edge. Under
the markers the heatmap is built 150 ms after the data or filter changes.

changelog.d/1426-fire-intensity-filter.md

@@ -4,9 +4,9 @@
   log-scale minimum-FRP slider whose track is the ramp, an All / Nominal+ /
   High confidence switch and an "N of M shown" counter to the layer row. Far
   zoom shows a Snap Map–style heatmap in the same colors instead of squares,
-  one distinct spot per fire, empty where nothing burns, with a ½×–4× spot
-  size slider. The filter applies once before rendering, so markers, cards,
-  the heatmap, context and the top-fires query agree; share links keep the
-  filter and the spot size (`w` token: `f`, `c`, `s`), and `get_active_fires`
+  one distinct spot per fire, empty where nothing burns, and cross-fades with
+  the markers around 3,000 km with no gap. The filter applies once before
+  rendering, so markers, cards, the heatmap, context and the top-fires query
+  agree; share links keep it (`w` token: `f`, `c`), and `get_active_fires`
   takes matching `min_frp_mw` and `confidence` arguments. Default 0 MW / All
-  / 1× (gekh, #1426).
+  (gekh, #1426).

docs/CURRENT-STATE.md

@@ -2209,37 +2209,36 @@ At far zoom (camera above ~3,000 km) the layer drapes a Snap Map–style
 heatmap instead of individual markers: the shown detections are linearly binned
 (each detection's weight shared between the four nearest pixel centres, so spots
 sit at the true position and stay round) on a
-global 2048 × 1024 grid (≈20 km per pixel), each weighted by its FRP in megawatts (so heat is
+global 4096 × 2048 grid (≈10 km per pixel), each weighted by its FRP in megawatts (so heat is
 radiated power, and raising the FRP slider does not dim areas where strong fires
-burn), Gaussian-blurred by one pixel so each fire stays a distinct spot about
-twice the size of its marker,
+burn, and a cluster of detections reads brighter than one), Gaussian-blurred by one
+pixel so each fire stays a distinct spot about the size of its marker,
 normalized on a log scale against the 99.5th percentile and mapped through the
 same hues, from a bright red edge through orange and gold to a pale
 white-hot core. The edge starts more than half opaque, so regions far below
 the hottest ones still read over forest and savanna imagery. Nothing is painted where
 nothing burns (`src/data/firmsHeatRaster.js`). It is one full-globe imagery
 tile on the active imagery host (`src/layers/firms/heatImagery.js`), rebuilt
-on each data refresh or filter change (the first paint at once, later ones
-150 ms after the last change) and hidden once markers take over below
-~750 km. "N FIRES" cards from a 2° / 1° aggregation still label the hottest
+on each data refresh or filter change (the first far-band paint at once,
+later ones 150 ms after the last change). Heatmap and markers are both kept
+built at every zoom and cross-fade by camera height between 2,400 and
+3,600 km, every frame, so a fast zoom never shows a gap: the heatmap fades by
+imagery `alpha` (a hidden Cesium imagery layer is unmapped from the globe
+tiles and re-mapped late when shown), the markers by sprite alpha, and the
+marker collection is hidden once the heatmap is whole. "N FIRES" cards from a 2° / 1° aggregation still label the hottest
 areas; their accent is the strongest fire's FRP color.
 
 The Active Fires row carries a "Fire intensity (FRP)" slider on a log scale
 whose track is painted with the ramp and ticked at the same six values (its
 value reads "All" or "≥ N MW"), a "Confidence" switch with All / Nominal+ /
-High, a "Heatmap spot size" slider (½× to 4× on a log2 axis, 5 % steps,
-default 1×) and an "N of M shown" counter. The spot size scales the heat
-grid rather than the blur (2× is a 1024 × 512 grid with the same one-pixel
-blur), so every spot grows exactly and weak lone fires do not fade as they
-widen; changing it rebuilds only the heatmap, not the shown set. The default is 0 MW and
+High, and an "N of M shown" counter. The default is 0 MW and
 All, because many of the strongest detections are rated low confidence. The
 filter runs once in `ingestion.applyFilter()` before rendering, so markers,
 cards, the heatmap, the shared context store, the top-fires query and the
 analyst records all see one filtered set; a selected fire that no longer passes
-is deselected. The layer state keeps the options under the `w` (`local-firms`)
-share token as `f` (whole megawatts, 0–10,000), `c` (`a`, `n`, `h`) and `s`
-(spot size in percent, 50–400), including the short share codec; a link
-without them restores the defaults.
+is deselected. The layer state keeps both options under the `w` (`local-firms`)
+share token as `f` (whole megawatts, 0–10,000) and `c` (`a`, `n`, `h`),
+including the short share codec; a link without them restores the defaults.
 
 The `get_active_fires` tool accepts its own `min_frp_mw` and `confidence`
 (`all`, `nominal`, `high`) arguments, independent of the panel's setting, and

src/data/firmsHeatRaster.js

@@ -43,70 +43,6 @@ export function heatColorAt(t) {
   ];
 }
 
-/**
- * Spot size, in percent of the shipped size: the panel slider and share
- * option `w.s`. Whole percents, half to four times.
- */
-export const HEAT_SPOT_SIZE_MIN = 50;
-export const HEAT_SPOT_SIZE_MAX = 400;
-export const HEAT_SPOT_SIZE_DEFAULT = 100;
-
-/**
- * Spot size → whole percent inside the bounds, or null.
- * @param {*} value
- * @returns {?number}
- */
-export function normalizeHeatSpotSize(value) {
-  const number =
-    typeof value === 'number'
-      ? value
-      : typeof value === 'string' && value.trim() !== ''
-        ? Number(value)
-        : NaN;
-  if (!Number.isFinite(number)) return null;
-  const rounded = Math.round(number);
-  return rounded >= HEAT_SPOT_SIZE_MIN && rounded <= HEAT_SPOT_SIZE_MAX
-    ? rounded
-    : null;
-}
-
-/**
- * The grid for a spot size. The same one-pixel blur on a grid that many
- * times coarser (or finer) scales every spot exactly; widening the blur
- * instead lowers each spot's peak, so weak lone fires faded as they grew.
- * @param {{width: number, height: number, sigmaPx: number}} base Shipped grid.
- * @param {number} spotSize Percent of the shipped size.
- * @returns {{width: number, height: number, sigmaPx: number}}
- */
-export function heatGridForSpotSize(base, spotSize) {
-  const percent = normalizeHeatSpotSize(spotSize) ?? HEAT_SPOT_SIZE_DEFAULT;
-  const height = Math.round((base.height * HEAT_SPOT_SIZE_DEFAULT) / percent);
-  return { width: height * 2, height, sigmaPx: base.sigmaPx };
-}
-
-/**
- * Slider axis for the spot size: log2, so ½× and 2× sit equally far from 1×.
- * Values snap to 5 % steps, which is also their share-link form.
- */
-const SPOT_LOG_MIN = Math.log2(HEAT_SPOT_SIZE_MIN / 100);
-const SPOT_LOG_SPAN = Math.log2(HEAT_SPOT_SIZE_MAX / 100) - SPOT_LOG_MIN;
-
-/** Track position in 0..1 for a spot size in percent. */
-export function sliderPositionForSpotSize(spotSize) {
-  const percent = normalizeHeatSpotSize(spotSize) ?? HEAT_SPOT_SIZE_DEFAULT;
-  return (Math.log2(percent / 100) - SPOT_LOG_MIN) / SPOT_LOG_SPAN;
-}
-
-/** Spot size in percent for a track position in 0..1. */
-export function spotSizeForSliderPosition(position) {
-  const p = Number.isFinite(position) ? Math.max(0, Math.min(1, position)) : 0;
-  const percent = 100 * Math.pow(2, SPOT_LOG_MIN + p * SPOT_LOG_SPAN);
-  return Math.min(
-    HEAT_SPOT_SIZE_MAX,
-    Math.max(HEAT_SPOT_SIZE_MIN, Math.round(percent / 5) * 5),
-  );
-}
-
 /** Weight of a detection with no or zero FRP, in megawatts. */
 export const HEAT_MIN_WEIGHT_MW = 0.5;
 

src/data/firmsHeatRaster.test.mjs

@@ -7,10 +7,6 @@ import {
   binFires,
   blurGaussian,
   buildHeatRaster,
-  heatGridForSpotSize,
-  normalizeHeatSpotSize,
-  sliderPositionForSpotSize,
-  spotSizeForSliderPosition,
 } from './firmsHeatRaster.js';
 
 const fire = (lat, lon, frp = 10) => ({ lat, lon, frp });
@@ -120,60 +116,3 @@ test('buildHeatRaster with no fires is fully transparent', () => {
   const r = buildHeatRaster([], { width: 8, height: 4, sigmaPx: 1 });
   assert.ok(r.rgba.every((v) => v === 0));
 });
-
-test('a spot size scales the grid, not the blur', () => {
-  const base = { width: 2048, height: 1024, sigmaPx: 1 };
-  assert.deepEqual(heatGridForSpotSize(base, 100), base);
-  assert.deepEqual(heatGridForSpotSize(base, 200), {
-    width: 1024,
-    height: 512,
-    sigmaPx: 1,
-  });
-  assert.deepEqual(heatGridForSpotSize(base, 50), {
-    width: 4096,
-    height: 2048,
-    sigmaPx: 1,
-  });
-  const odd = heatGridForSpotSize(base, 150);
-  assert.equal(odd.width, odd.height * 2, 'the grid stays 2:1');
-  assert.deepEqual(heatGridForSpotSize(base, 9999), base, 'invalid → default');
-});
-
-test('twice the spot size paints a lone fire twice as wide', () => {
-  const base = { width: 2048, height: 1024, sigmaPx: 1 };
-  const fires = [fire(0, 0, 5)];
-  for (let i = 0; i < 40; i++) fires.push(fire(-10, 25 + i * 0.05, 300));
-  const widthKm = (spotSize) => {
-    const r = buildHeatRaster(fires, heatGridForSpotSize(base, spotSize));
-    const y = Math.floor(r.height / 2);
-    let painted = 0;
-    for (let x = 0; x < r.width; x++) {
-      const lon = ((x + 0.5) / r.width) * 360 - 180;
-      if (Math.abs(lon) < 10 && r.rgba[(y * r.width + x) * 4 + 3] > 0) {
-        painted += 1;
-      }
-    }
-    return (painted * 40075) / r.width;
-  };
-  const ratio = widthKm(200) / widthKm(100);
-  assert.ok(ratio > 1.7 && ratio < 2.3, `ratio ${ratio.toFixed(2)}`);
-});
-
-test('the spot-size slider is log2 with 1x a third along and 5 % steps', () => {
-  assert.equal(sliderPositionForSpotSize(50), 0);
-  assert.equal(sliderPositionForSpotSize(400), 1);
-  assert.ok(Math.abs(sliderPositionForSpotSize(100) - 1 / 3) < 1e-9);
-  assert.ok(Math.abs(sliderPositionForSpotSize(200) - 2 / 3) < 1e-9);
-  assert.equal(spotSizeForSliderPosition(0), 50);
-  assert.equal(spotSizeForSliderPosition(1), 400);
-  assert.equal(spotSizeForSliderPosition(1 / 3), 100);
-  assert.equal(spotSizeForSliderPosition(-1), 50);
-  for (let i = 0; i <= 100; i++) {
-    const percent = spotSizeForSliderPosition(i / 100);
-    assert.equal(percent % 5, 0, `${percent} at ${i}%`);
-    assert.equal(normalizeHeatSpotSize(percent), percent);
-  }
-  assert.equal(normalizeHeatSpotSize('150'), 150);
-  assert.equal(normalizeHeatSpotSize(49), null);
-  assert.equal(normalizeHeatSpotSize(''), null);
-});

src/data/firmsInteraction.test.mjs

@@ -15,6 +15,7 @@ import { WORLD_FOCUS_REQUEST_EVENT } from '../worldFocus.js';
 import { readLayerSource } from '../testSupport/readLayerSource.mjs';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
+import { HEAT_REBUILD_MS } from '../layers/firms/policy.js';
 
 const LAYER_SOURCE = readLayerSource(
   path.join(path.dirname(fileURLToPath(import.meta.url)), 'firmsHeatmap.js'),
@@ -393,7 +394,58 @@ test('disable cancels a pending source and a late response cannot repopulate the
   } finally { h.layer.destroy(h.viewer); h.cleanup(); }
 });
 
-test('far zoom drapes one heatmap and draws no rectangles; markers and disable hide it', () => {
+test('the heatmap is preloaded under the markers before the first zoom-out', (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  const priorDocument = globalThis.document;
+  globalThis.document = {
+    createElement: () => ({
+      getContext: () => ({
+        createImageData: (w, hh) => ({ data: new Uint8ClampedArray(w * hh * 4) }),
+        putImageData() {},
+        createRadialGradient: () => ({ addColorStop() {} }),
+        fillRect() {},
+      }),
+      toDataURL: () => 'data:image/png;base64,AAAA',
+    }),
+  };
+  const h = harness({
+    withDataSource: true,
+    cameraPosition: Cesium.Cartesian3.fromDegrees(-98, 30, 1_000_000),
+  });
+  h.viewer.camera = { positionCartographic: { height: 1_000_000 } };
+  h.viewer.scene.primitives = { add() {}, remove() {}, raiseToTop() {}, contains: () => true };
+  h.viewer.scene.frameState = { mode: Cesium.SceneMode.SCENE3D };
+  const added = [];
+  try {
+    h.layer.attachShellServices({
+      imageryHost: () => ({
+        kind: 'globe',
+        collection: {
+          addImageryProvider: (provider) => {
+            const layer = { provider, show: true, alpha: 1 };
+            added.push(layer);
+            return layer;
+          },
+          remove() {},
+          raiseToTop() {},
+        },
+      }),
+    });
+    h.layer._renderLodForTest('close');
+    assert.equal(added.length, 0, 'the markers paint first; the build trails');
+    t.mock.timers.tick(HEAT_REBUILD_MS);
+    assert.equal(added.length, 1, 'then the heatmap is draped');
+    assert.equal(added[0].alpha, 0, 'invisible until the hand-off');
+    assert.equal(added[0].show, true, 'but mapped onto the globe tiles');
+  } finally {
+    h.layer.destroy(h.viewer);
+    h.cleanup();
+    if (priorDocument === undefined) delete globalThis.document;
+    else globalThis.document = priorDocument;
+  }
+});
+
+test('far zoom drapes one heatmap and the hand-off cross-fades it with the markers', () => {
   // A canvas stub for the heat drape and the detection glow sprites.
   const priorDocument = globalThis.document;
   const restoreDocument = () => {
@@ -420,8 +472,16 @@ test('far zoom drapes one heatmap and draws no rectangles; markers and disable h
   });
   const added = [];
   const removed = [];
+  let markers = null;
+  // The fade reads the camera height; the cull reads scene.camera.
+  const setHeight = (height) => {
+    h.viewer.camera = { positionCartographic: { height } };
+  };
+  setHeight(12_000_000);
   h.viewer.scene.primitives = {
-    add() {},
+    add(primitive) {
+      markers = primitive;
+    },
     remove() {},
     raiseToTop() {},
     contains: () => true,
@@ -430,7 +490,7 @@ test('far zoom drapes one heatmap and draws no rectangles; markers and disable h
   try {
     const collection = {
       addImageryProvider: (provider) => {
-        const layer = { provider, show: true };
+        const layer = { provider, show: true, alpha: 1 };
         added.push(layer);
         return layer;
       },
@@ -443,17 +503,33 @@ test('far zoom drapes one heatmap and draws no rectangles; markers and disable h
     h.layer._renderLodForTest('global');
     assert.equal(added.length, 1, 'one heat imagery layer');
     assert.equal(added[0].show, true);
+    assert.equal(added[0].alpha, 1);
     assert.equal(h.layer._entityCountForTest(), 0, 'no rectangle entities');
     assert.ok(h.published.length > 0, 'the far band still paints cards');
+    assert.equal(markers.length, 2, 'the markers are built under the heatmap');
+    assert.equal(markers.show, false, 'and hidden while the heatmap is whole');
 
     h.layer._renderLodForTest('regional');
     assert.equal(added.length, 1, 'switching far bands reuses the raster');
 
+    setHeight(1_000_000);
     h.layer._renderLodForTest('close');
-    assert.equal(added[0].show, false, 'the markers band hides the heatmap');
+    assert.equal(added.length, 1, 'the markers band keeps the same heat layer');
+    assert.equal(added[0].show, true, 'still mapped onto the globe tiles');
+    assert.equal(added[0].alpha, 0, 'faded out under the markers');
+    assert.equal(markers.show, true);
+    assert.equal(markers.get(0).color.alpha, 1);
+
+    // Mid hand-off both are drawn, half each, in either band.
+    setHeight(3_000_000);
+    h.layer._applyHandoffFadeForTest();
+    assert.equal(added[0].alpha, 0.5);
+    assert.equal(markers.show, true);
+    assert.equal(markers.get(0).color.alpha, 0.5);
+    h.layer._renderLodForTest('regional');
+    assert.equal(added[0].alpha, 0.5);
+    assert.equal(markers.get(1).color.alpha, 0.5, 'rebuilt markers get the fade');
 
-    h.layer._renderLodForTest('global');
-    assert.equal(added[0].show, true);
     h.layer.disable();
     assert.equal(added[0].show, false, 'disable hides the heatmap');
 
@@ -467,66 +543,3 @@ test('far zoom drapes one heatmap and draws no rectangles; markers and disable h
     restoreDocument();
   }
 });
-
-test('the spot-size slider rebuilds only the heatmap, on a proportionally coarser grid', async () => {
-  const priorDocument = globalThis.document;
-  const grids = [];
-  globalThis.document = {
-    createElement: () => ({
-      getContext: () => ({
-        createImageData: (w, hh) => {
-          grids.push([w, hh]);
-          return { data: new Uint8ClampedArray(w * hh * 4) };
-        },
-        putImageData() {},
-        createRadialGradient: () => ({ addColorStop() {} }),
-        fillRect() {},
-      }),
-      toDataURL: () => 'data:image/png;base64,AAAA',
-    }),
-  };
-  const h = harness({
-    fires: [makeFire(), makeFire({ index: 8, lat: 30.6, lon: -98.3, frp: 12 })],
-    withDataSource: true,
-    cameraPosition: Cesium.Cartesian3.fromDegrees(-98, 30, 12_000_000),
-  });
-  h.viewer.scene.primitives = { add() {}, remove() {}, raiseToTop() {}, contains: () => true };
-  h.viewer.scene.frameState = { mode: Cesium.SceneMode.SCENE3D };
-  const collection = {
-    addImageryProvider: (provider) => ({ provider, show: true }),
-    remove() {},
-    raiseToTop() {},
-  };
-  try {
-    h.layer.attachShellServices({ imageryHost: () => ({ kind: 'globe', collection }) });
-    h.layer._renderLodForTest('global');
-    assert.deepEqual(grids.at(-1), [2048, 1024]);
-    assert.deepEqual(
-      h.layer.getRowControls().sliders.map((slider) => slider.id),
-      ['min-frp', 'heat-spot-size'],
-    );
-    const spot = h.layer.getRowControls().sliders[1];
-    assert.equal(spot.valueText, '1×');
-    assert.deepEqual(spot.params(1000), { spotSize: 400 });
-
-    let repaints = 0;
-    h.layer.setRowControlsListener(() => repaints++);
-    h.layer.setParams({ spotSize: 200 });
-    assert.equal(h.layer.getParams().spotSize, 200);
-    assert.equal(h.layer.getParams().minFrp, 0, 'the filter is untouched');
-    assert.equal(h.layer.getStats().count, 2, 'every fire still shown');
-    assert.equal(repaints, 1, 'the row repaints its value');
-    assert.equal(h.layer.getRowControls().sliders[1].valueText, '2×');
-    // The rebuild trails a drag (HEAT_REBUILD_MS) and keeps the old drape meanwhile.
-    await new Promise((resolve) => setTimeout(resolve, 200));
-    assert.deepEqual(grids.at(-1), [1024, 512]);
-
-    h.layer.setParams({ spotSize: 'nope' });
-    assert.equal(h.layer.getParams().spotSize, 200, 'invalid input is ignored');
-  } finally {
-    h.layer.destroy(h.viewer);
-    h.cleanup();
-    if (priorDocument === undefined) delete globalThis.document;
-    else globalThis.document = priorDocument;
-  }
-});

src/data/layerState.js

@@ -298,7 +298,7 @@ function satelliteFilterOption() {
 }
 
 const OPTION_GROUPS = Object.freeze({
-  // Active Fires intensity filter and heatmap spot size (HAL-676). `minFrp` is whole megawatts on
+  // Active Fires intensity filter (HAL-676). `minFrp` is whole megawatts on
   // the codec side; the panel's log slider rounds to it. Both default to
   // "show everything": many of the strongest fires are rated low confidence.
   // The bounds and modes mirror MIN_FRP_MW_MAX / FIRMS_CONFIDENCE_MODES in
@@ -311,9 +311,6 @@ const OPTION_GROUPS = Object.freeze({
       nominal: 'n',
       high: 'h',
     }),
-    // Heatmap spot size in percent; mirrors HEAT_SPOT_SIZE_* in
-    // firmsHeatRaster.js.
-    boundedIntegerOption('spotSize', 's', 100, { min: 50, max: 400 }),
   ]),
   traffic: Object.freeze([
     enumOption('roadMode', 'r', null, ['tomtom', 'osm', 'hybrid'], {

src/data/layerState.test.mjs

@@ -30,11 +30,6 @@ import { stampInitialShareGesture } from '../navigationPolicy.js';
 import { MAX_SINCE_DAYS } from '../layers/streetLevel/policy.js';
 import { SINCE_STOPS } from '../ui/streetLevelPresentation.js';
 import { FIRMS_CONFIDENCE_MODES, MIN_FRP_MW_MAX } from './firmsIntensity.js';
-import {
-  HEAT_SPOT_SIZE_DEFAULT,
-  HEAT_SPOT_SIZE_MAX,
-  HEAT_SPOT_SIZE_MIN,
-} from './firmsHeatRaster.js';
 
 function deferred() {
   let resolve;
@@ -3024,14 +3019,9 @@ test('Active Fires: the intensity filter rides share token w and round-trips', (
   assert.deepEqual(state.options['local-firms'], {
     minFrp: 0,
     confidence: 'all',
-    spotSize: 100,
   });
   state.enabledLayerIds = ['local-firms'];
-  state.options['local-firms'] = {
-    minFrp: 20,
-    confidence: 'high',
-    spotSize: 250,
-  };
+  state.options['local-firms'] = { minFrp: 20, confidence: 'high' };
   const encoded = encode(state);
   assert.equal(new URLSearchParams(encoded).get('l'), 'w');
   // Other owners write their own explicit defaults into `lo` too (flights 3D,
@@ -3039,12 +3029,10 @@ test('Active Fires: the intensity filter rides share token w and round-trips', (
   const assignments = new URLSearchParams(encoded).get('lo').split('_');
   assert.ok(assignments.includes('w.f.20'), assignments.join(' '));
   assert.ok(assignments.includes('w.c.h'), assignments.join(' '));
-  assert.ok(assignments.includes('w.s.250'), assignments.join(' '));
   const decoded = decodeLayerStateParams(new URLSearchParams(encoded));
   assert.deepEqual(decoded.options['local-firms'], {
     minFrp: 20,
     confidence: 'high',
-    spotSize: 250,
   });
   assert.deepEqual(
     parseStoredLayerState(serializeStoredLayerState(state)).options[
@@ -3062,11 +3050,7 @@ test('Active Fires: the intensity filter rides share token w and round-trips', (
       .filter((assignment) => assignment.startsWith('w.')).length,
     0,
   );
-  assert.deepEqual(firmsOptions(''), {
-    minFrp: 0,
-    confidence: 'all',
-    spotSize: 100,
-  });
+  assert.deepEqual(firmsOptions(''), { minFrp: 0, confidence: 'all' });
 });
 
 test('Active Fires: the codec accepts whole megawatts in bounds and the three confidence codes', () => {
@@ -3094,17 +3078,5 @@ test('Active Fires: the codec accepts whole megawatts in bounds and the three co
   assert.deepEqual(firmsOptions('w.c.n_w.f.5'), {
     minFrp: 5,
     confidence: 'nominal',
-    spotSize: 100,
   });
 });
-
-test('Active Fires: the codec accepts whole-percent spot sizes from half to four times', () => {
-  assert.equal(HEAT_SPOT_SIZE_MIN, 50);
-  assert.equal(HEAT_SPOT_SIZE_MAX, 400);
-  assert.equal(HEAT_SPOT_SIZE_DEFAULT, 100);
-  assert.equal(firmsOptions('w.s.50').spotSize, 50);
-  assert.equal(firmsOptions('w.s.400').spotSize, 400);
-  assert.equal(firmsOptions('w.s.45').spotSize, 100, 'out of bounds → default');
-  assert.equal(firmsOptions('w.s.401').spotSize, 100);
-  assert.equal(firmsOptions('w.s.x').spotSize, 100);
-});

src/i18n/locales/ar.json

@@ -3224,9 +3224,6 @@
   "≥ {value} MW": "{value} MW على الأقل",
   "Confidence": "الثقة",
   "Minimum fire radiative power, megawatts": "الحد الأدنى للقدرة الإشعاعية للحريق، بالميغاواط",
-  "Heatmap spot size": "حجم بقع الخريطة الحرارية",
-  "Far-zoom heatmap spot size": "حجم بقع الخريطة الحرارية عند العرض البعيد",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "الكل",
   "Detection confidence": "ثقة الرصد",
   "{shown} of {total} shown": "المعروضة: {shown} من {total}",

src/i18n/locales/de.json

@@ -2944,9 +2944,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "Konfidenz",
   "Minimum fire radiative power, megawatts": "Minimale Strahlungsleistung des Brandes in Megawatt",
-  "Heatmap spot size": "Fleckengröße der Heatmap",
-  "Far-zoom heatmap spot size": "Fleckengröße der Heatmap in der Fernansicht",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Alle",
   "Detection confidence": "Konfidenz der Erkennung",
   "{shown} of {total} shown": "{shown} von {total} angezeigt",

src/i18n/locales/es.json

@@ -2993,9 +2993,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "Confianza",
   "Minimum fire radiative power, megawatts": "Potencia radiativa mínima del fuego, en megavatios",
-  "Heatmap spot size": "Tamaño de las manchas del mapa de calor",
-  "Far-zoom heatmap spot size": "Tamaño de las manchas del mapa de calor en la vista lejana",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Todo",
   "Detection confidence": "Confianza de la detección",
   "{shown} of {total} shown": "{shown} de {total} mostrados",

src/i18n/locales/fr.json

@@ -3014,9 +3014,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "Confiance",
   "Minimum fire radiative power, megawatts": "Puissance radiative minimale du feu, en mégawatts",
-  "Heatmap spot size": "Taille des taches de la carte de chaleur",
-  "Far-zoom heatmap spot size": "Taille des taches de la carte de chaleur en vue éloignée",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Toutes",
   "Detection confidence": "Confiance de la détection",
   "{shown} of {total} shown": "{shown} sur {total} affichées",

src/i18n/locales/it.json

@@ -3014,9 +3014,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "Confidenza",
   "Minimum fire radiative power, megawatts": "Potenza radiativa minima dell'incendio, in megawatt",
-  "Heatmap spot size": "Dimensione delle macchie della mappa di calore",
-  "Far-zoom heatmap spot size": "Dimensione delle macchie della mappa di calore nella vista da lontano",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Tutti",
   "Detection confidence": "Confidenza del rilevamento",
   "{shown} of {total} shown": "{shown} di {total} mostrati",

src/i18n/locales/ja.json

@@ -2874,9 +2874,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "信頼度",
   "Minimum fire radiative power, megawatts": "火災放射強度の最小値（メガワット）",
-  "Heatmap spot size": "ヒートマップの点の大きさ",
-  "Far-zoom heatmap spot size": "遠景ヒートマップの点の大きさ",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "すべて",
   "Detection confidence": "検知の信頼度",
   "{shown} of {total} shown": "{total}件中{shown}件を表示",

src/i18n/locales/pt.json

@@ -3014,9 +3014,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "Confiança",
   "Minimum fire radiative power, megawatts": "Potência radiativa mínima do fogo, em megawatts",
-  "Heatmap spot size": "Tamanho das manchas do mapa de calor",
-  "Far-zoom heatmap spot size": "Tamanho das manchas do mapa de calor na vista distante",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Todas",
   "Detection confidence": "Confiança da detecção",
   "{shown} of {total} shown": "{shown} de {total} exibidas",

src/i18n/locales/ru.json

@@ -3063,9 +3063,6 @@
   "≥ {value} MW": "≥ {value} МВт",
   "Confidence": "Достоверность",
   "Minimum fire radiative power, megawatts": "Минимальная мощность излучения пожара, мегаватты",
-  "Heatmap spot size": "Размер пятен тепловой карты",
-  "Far-zoom heatmap spot size": "Размер пятен тепловой карты на дальнем масштабе",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Все",
   "Detection confidence": "Достоверность детекции",
   "{shown} of {total} shown": "показано {shown} из {total}",

src/i18n/locales/uk.json

@@ -3055,9 +3055,6 @@
   "≥ {value} MW": "≥ {value} МВт",
   "Confidence": "Достовірність",
   "Minimum fire radiative power, megawatts": "Мінімальна потужність випромінювання пожежі, мегавати",
-  "Heatmap spot size": "Розмір плям теплової карти",
-  "Far-zoom heatmap spot size": "Розмір плям теплової карти на далекому масштабі",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "Усі",
   "Detection confidence": "Достовірність виявлення",
   "{shown} of {total} shown": "показано {shown} з {total}",

src/i18n/locales/zh-CN.json

@@ -2853,9 +2853,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "置信度",
   "Minimum fire radiative power, megawatts": "最小火辐射功率（兆瓦）",
-  "Heatmap spot size": "热力图光斑大小",
-  "Far-zoom heatmap spot size": "远景热力图光斑大小",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "全部",
   "Detection confidence": "检测置信度",
   "{shown} of {total} shown": "显示 {shown} / {total}",

src/i18n/locales/zh-Hant.json

@@ -2880,9 +2880,6 @@
   "≥ {value} MW": "≥ {value} MW",
   "Confidence": "置信度",
   "Minimum fire radiative power, megawatts": "最小火輻射功率（兆瓦）",
-  "Heatmap spot size": "熱力圖光斑大小",
-  "Far-zoom heatmap spot size": "遠景熱力圖光斑大小",
-  "{value}×": "{value}×",
   "fire intensity filter|All": "全部",
   "Detection confidence": "檢測置信度",
   "{shown} of {total} shown": "顯示 {shown} / {total}",

src/i18n/same-as-english.json

@@ -31,7 +31,6 @@
     "dB",
     "hPa",
     "{source} HTTP {status}",
-    "{value}×",
     "▲ {frp} MW"
   ],
   "de": [
@@ -198,7 +197,6 @@
     "{value} KM DOWNRANGE",
     "{value} KM/H",
     "{value} KM/S",
-    "{value}×",
     "ΔN",
     "Ⅱ PAUSE",
     "≥ {value} MW",
@@ -329,7 +327,6 @@
     "{value} KM",
     "{value} KM/H",
     "{value} KM/S",
-    "{value}×",
     "≥ {value} MW",
     "ΔE",
     "ΔN",
@@ -511,7 +508,6 @@
     "{value} KM",
     "{value} KM/H",
     "{value} KM/S",
-    "{value}×",
     "ΔE",
     "ΔN",
     "Ⅱ PAUSE",
@@ -685,7 +681,6 @@
     "{value} KM/H",
     "{value} KM/S",
     "{value} conf",
-    "{value}×",
     "≥ {value} MW",
     "ΔE",
     "ΔN",
@@ -736,7 +731,6 @@
     "{source} HTTP {status}",
     "{speed} kn",
     "{type}  SPD: {speed}  HDG: {heading}",
-    "{value}×",
     "ΔE",
     "ΔN",
     "≥ {value} MW",
@@ -871,7 +865,6 @@
     "{value} KM/S",
     "ΔN",
     "▲ {frp} MW",
-    "{value}×",
     "≥ {value} MW"
   ],
   "ru": [
@@ -890,8 +883,7 @@
     "S2 GhostMaps",
     "S2 · {name}",
     "VS",
-    "WHOT/BHOT",
-    "{value}×"
+    "WHOT/BHOT"
   ],
   "uk": [
     "AIS: --",
@@ -904,8 +896,7 @@
     "NVG",
     "REC",
     "S2 GhostMaps",
-    "WHOT/BHOT",
-    "{value}×"
+    "WHOT/BHOT"
   ],
   "zh-CN": [
     "1090 MHz",
@@ -960,7 +951,6 @@
     "{type}  SPD: {speed}  HDG: {heading}",
     "{value} KM",
     "{value} KM/S",
-    "{value}×",
     "≥ {value} MW",
     "ΔE",
     "ΔN",
@@ -1019,7 +1009,6 @@
     "{type}  SPD: {speed}  HDG: {heading}",
     "{value} KM",
     "{value} KM/S",
-    "{value}×",
     "≥ {value} MW",
     "ΔE",
     "ΔN",

src/layers/firms/heatImagery.js

@@ -3,6 +3,12 @@
  * imagery tile on the active imagery host (globe or 3D-tiles), like the wind
  * layer's scalar field. Owns the canvas and the imagery layer; nothing else
  * in the fires layer touches imagery.
+ *
+ * `show` is only for the layer being on or off. The zoom hand-off fades
+ * `alpha` instead: Cesium unmaps a hidden imagery layer from the globe
+ * tiles and re-maps it when shown, so a show toggle at the band edge left
+ * a beat with neither markers nor heat. At alpha 0 the layer stays mapped
+ * and costs no draw.
  */
 
 const defaultCanvas = (width, height) => {
@@ -21,6 +27,7 @@ export function createHeatImagery({
   let layer = null;
   let collection = null;
   let show = true;
+  let opacity = 1;
 
   function detach() {
     if (layer && collection) collection.remove(layer, true);
@@ -47,6 +54,7 @@ export function createHeatImagery({
     collection = host.collection;
     layer = collection.addImageryProvider(provider);
     layer.show = show;
+    layer.alpha = opacity;
     collection.raiseToTop?.(layer);
   }
 
@@ -63,6 +71,11 @@ export function createHeatImagery({
       show = Boolean(value);
       if (layer) layer.show = show;
     },
+    /** Hand-off fade, 0..1; the layer stays mapped at 0. */
+    setOpacity(value) {
+      opacity = Math.min(1, Math.max(0, Number(value) || 0));
+      if (layer) layer.alpha = opacity;
+    },
     rehome() {
       const host = getHost?.();
       if ((host?.collection ?? null) !== collection) attach();

src/layers/firms/heatImagery.test.mjs

@@ -71,6 +71,22 @@ test('setShow toggles without rebuilding', () => {
   assert.equal(layer.show, true);
 });
 
+test('setOpacity fades the same layer and survives a rebuild', () => {
+  const h = harness();
+  h.imagery.setRaster(raster);
+  const layer = h.layers[0];
+  h.imagery.setOpacity(0);
+  assert.equal(layer.alpha, 0);
+  assert.equal(layer.show, true, 'a faded layer stays mapped');
+  h.imagery.setOpacity(0.25);
+  assert.equal(h.layers[0], layer);
+  assert.equal(layer.alpha, 0.25);
+  h.imagery.setRaster(raster);
+  assert.equal(h.layers[0].alpha, 0.25, 'a rebuilt layer keeps the fade');
+  h.imagery.setOpacity(7);
+  assert.equal(h.layers[0].alpha, 1);
+});
+
 test('no imagery host keeps nothing draped; rehome brings it back', () => {
   const h = harness();
   h.setHost({ collection: null, kind: 'none' });

src/layers/firms/lifecycle.js

@@ -1,6 +1,5 @@
 import * as Cesium from 'cesium';
 import { FIRMS_OVERLAY_SOURCE_ID } from '../../data/firmsLabels.js';
-import { LOD_LEVELS } from './policy.js';
 
 export function createLifecycle({
   layerState,
@@ -55,8 +54,9 @@ export function createLifecycle({
         layerState._billboards.show = true;
       }
       overlayHost.setVisible(FIRMS_OVERLAY_SOURCE_ID, true);
-      if (LOD_LEVELS[layerState._currentLodIndex]?.mode === 'heat')
-        layerState._heatImagery?.setShow(true);
+      layerState._heatImagery?.setShow(true);
+      // The camera can have crossed the hand-off while the layer was off.
+      components.rendering.applyHandoffFade(true);
       components.viewport.installLodWatcher();
       components.viewport.installMoveEndWatcher();
       components.selection.installClickHandler();
@@ -119,6 +119,7 @@ export function createLifecycle({
       layerState._heatImagery?.destroy();
       layerState._heatImagery = null;
       layerState._heatRaster = null;
+      layerState._handoffHeat = -1;
       layerState._imageryHost = null;
       layerState._count = 0;
       layerState._totalCount = 0;

src/layers/firms/policy.js

@@ -49,20 +49,29 @@ export const LOD_LEVELS = [
 ];
 
 /**
- * Global heat raster for the `heat` bands: ≈0.18° (≈20 km) per pixel and a
- * one-pixel Gaussian σ, so a lone fire is a distinct spot about twice as wide
- * as its marker at the 3,000 km hand-off and still reads from the
- * whole-globe view; neighbours merge only when they nearly touch (σ 3 here
- * smeared each fire over ~200 km). Built once per data refresh or filter
- * change, never per camera move.
+ * Global heat raster for the `heat` bands: ≈0.09° (≈10 km) per pixel and a
+ * one-pixel Gaussian σ, so a lone fire is a spot about the size of its
+ * marker at the 3,000 km hand-off and the two cross-fade without a jump;
+ * neighbours merge only when they nearly touch (σ 3 on a 2048 grid smeared
+ * each fire over ~200 km). Built once per data refresh or filter change,
+ * never per camera move.
  */
 
 export const HEAT_RASTER = Object.freeze({
-  width: 2048,
-  height: 1024,
+  width: 4096,
+  height: 2048,
   sigmaPx: 1,
 });
 
+/**
+ * Camera heights, in metres, over which the heatmap and the markers
+ * cross-fade around the 3,000 km band edge: markers alone below `from`,
+ * heatmap alone above `to`. Wider than the ±10 % band hysteresis, so
+ * whichever band is active inside it, both layers are already built.
+ */
+
+export const HANDOFF_FADE = Object.freeze({ from: 2_400_000, to: 3_600_000 });
+
 /**
  * Trailing delay before a stale heatmap is rebuilt while one is already on
  * screen: a slider drag fires many filter changes, and a build plus PNG

src/layers/firms/queries.js

@@ -8,11 +8,6 @@ import {
   rampTrackGradient,
   sliderPositionForFrp,
 } from '../../data/firmsIntensity.js';
-import {
-  normalizeHeatSpotSize,
-  sliderPositionForSpotSize,
-  spotSizeForSliderPosition,
-} from '../../data/firmsHeatRaster.js';
 import { formatNumber, t } from '../../i18n/index.js';
 import { LOD_LEVELS, REFRESH_INTERVAL_MS } from './policy.js';
 
@@ -28,16 +23,6 @@ export function createQueries({
 }) {
   const { id, name, icon, source } = config;
 
-  /** Spot sizes marked under the spot-size slider, in percent. */
-  const SPOT_SIZE_TICKS = [50, 100, 200, 400];
-
-  /** Spot-size label for a percent ("0.5×", "1×", "1.5×"). */
-  function spotSizeLabel(percent) {
-    return t('{value}×', {
-      value: formatNumber(percent / 100, { maximumFractionDigits: 2 }),
-    });
-  }
-
   /** Whole-megawatt label for a slider value or tick ("0", "20", "1 000"). */
   function frpLabel(frp) {
     return formatNumber(frp, { maximumFractionDigits: 0 });
@@ -98,12 +83,12 @@ export function createQueries({
     updateInterval: REFRESH_INTERVAL_MS,
 
     /**
-     * The intensity filter and the heatmap spot size as layer options (share
-     * token `w`, owner `local-firms` in layerState.js).
-     * @returns {{minFrp: number, confidence: string, spotSize: number}}
+     * The intensity filter as layer options (share token `w`, owner
+     * `local-firms` in layerState.js).
+     * @returns {{minFrp: number, confidence: string}}
      */
     getParams() {
-      return { ...layerState._filter, spotSize: layerState._spotSize };
+      return { ...layerState._filter };
     },
 
     /**
@@ -111,36 +96,24 @@ export function createQueries({
      * value. The filter runs in one place (ingestion.applyFilter) and the LOD
      * rebuild re-derives markers, cells, cards and context registrations from
      * the shown set; a selected fire that no longer passes is deselected.
-     * A spot-size change only marks the heat raster stale: the shown set,
-     * markers and cards stay as they are.
-     * @param {{minFrp?: number, confidence?: string, spotSize?: number}} params
+     * @param {{minFrp?: number, confidence?: string}} params
      * @returns {boolean} True — the request is always accepted.
      */
     setParams(params = {}) {
       const next = normalizeFireFilter(params, layerState._filter);
-      const spotSize =
-        normalizeHeatSpotSize(params?.spotSize) ?? layerState._spotSize;
-      const filterChanged =
-        next.minFrp !== layerState._filter.minFrp ||
-        next.confidence !== layerState._filter.confidence;
-      const spotChanged = spotSize !== layerState._spotSize;
-      if (!filterChanged && !spotChanged) return true;
-      layerState._filter = next;
-      layerState._spotSize = spotSize;
-      if (!layerState._allFires.length) {
-        layerState._rowControlsListener?.();
+      if (
+        next.minFrp === layerState._filter.minFrp &&
+        next.confidence === layerState._filter.confidence
+      )
         return true;
-      }
-      if (filterChanged) {
-        components.ingestion.applyFilter();
-        if (
-          layerState._selectedFire &&
-          !firePassesFilter(layerState._selectedFire, next)
-        ) {
-          components.selection.clearFireSelection();
-        }
-      } else {
-        layerState._heatRaster = null;
+      layerState._filter = next;
+      if (!layerState._allFires.length) return true;
+      components.ingestion.applyFilter();
+      if (
+        layerState._selectedFire &&
+        !firePassesFilter(layerState._selectedFire, next)
+      ) {
+        components.selection.clearFireSelection();
       }
       if (layerState._enabled) components.rendering.renderCurrentLod(true);
       layerState._rowControlsListener?.();
@@ -150,8 +123,8 @@ export function createQueries({
     /**
      * Row controls under the Active Fires row: the log-scale minimum-FRP
      * slider whose track is painted with the intensity ramp (so it doubles as
-     * the legend), the All / Nominal+ / High confidence switch, the far-zoom
-     * heatmap spot-size slider and the "N of M shown" counter.
+     * the legend), the All / Nominal+ / High confidence switch, and the
+     * "N of M shown" counter.
      */
     getRowControls() {
       const { minFrp, confidence } = layerState._filter;
@@ -160,48 +133,27 @@ export function createQueries({
       const shown = layerState._count;
       const total = layerState._totalCount;
       return {
-        sliders: [
-          {
-            id: 'min-frp',
-            label: t('Fire intensity (FRP)'),
-            ariaLabel: t('Minimum fire radiative power, megawatts'),
-            valueText:
-              minFrp > 0
-                ? t('≥ {value} MW', { value: frpLabel(minFrp) })
-                : t('All', { context: 'fire intensity filter' }),
-            min: 0,
-            max: SLIDER_STEPS,
-            step: 1,
-            value: Math.round(sliderPositionForFrp(minFrp) * SLIDER_STEPS),
-            track: rampTrackGradient(),
-            ticks: FRP_SLIDER_TICKS.map((frp) => ({
-              at: sliderPositionForFrp(frp),
-              label: frpLabel(frp),
-            })),
-            params: (value) => ({
-              minFrp: frpForSliderPosition(Number(value) / SLIDER_STEPS),
-            }),
-          },
-          {
-            id: 'heat-spot-size',
-            label: t('Heatmap spot size'),
-            ariaLabel: t('Far-zoom heatmap spot size'),
-            valueText: spotSizeLabel(layerState._spotSize),
-            min: 0,
-            max: SLIDER_STEPS,
-            step: 1,
-            value: Math.round(
-              sliderPositionForSpotSize(layerState._spotSize) * SLIDER_STEPS,
-            ),
-            ticks: SPOT_SIZE_TICKS.map((percent) => ({
-              at: sliderPositionForSpotSize(percent),
-              label: spotSizeLabel(percent),
-            })),
-            params: (value) => ({
-              spotSize: spotSizeForSliderPosition(Number(value) / SLIDER_STEPS),
-            }),
-          },
-        ],
+        slider: {
+          id: 'min-frp',
+          label: t('Fire intensity (FRP)'),
+          ariaLabel: t('Minimum fire radiative power, megawatts'),
+          valueText:
+            minFrp > 0
+              ? t('≥ {value} MW', { value: frpLabel(minFrp) })
+              : t('All', { context: 'fire intensity filter' }),
+          min: 0,
+          max: SLIDER_STEPS,
+          step: 1,
+          value: Math.round(sliderPositionForFrp(minFrp) * SLIDER_STEPS),
+          track: rampTrackGradient(),
+          ticks: FRP_SLIDER_TICKS.map((frp) => ({
+            at: sliderPositionForFrp(frp),
+            label: frpLabel(frp),
+          })),
+          params: (value) => ({
+            minFrp: frpForSliderPosition(Number(value) / SLIDER_STEPS),
+          }),
+        },
         segmented: {
           id: 'confidence',
           label: t('Confidence'),
@@ -359,10 +311,15 @@ export function createQueries({
 
     /** Test seam: render one named LOD band against a near-global view. */
     _renderLodForTest(lodId) {
-      const lod = LOD_LEVELS.find((level) => level.id === lodId);
-      if (lod.mode === 'detections')
-        components.rendering.renderDetections(lod, null);
-      else components.rendering.renderHeat(lod, null);
+      components.rendering.renderBand(
+        LOD_LEVELS.find((level) => level.id === lodId),
+        null,
+      );
+    },
+
+    /** Test seam: one frame of the hand-off fade at the current camera. */
+    _applyHandoffFadeForTest() {
+      components.rendering.applyHandoffFade();
     },
 
     /** Test seam: entities drawn by the layer's data source. */

src/layers/firms/rendering.js

@@ -1,18 +1,22 @@
 import * as Cesium from 'cesium';
 import { FIRMS_OVERLAY_SOURCE_ID } from '../../data/firmsLabels.js';
 import { horizonOccluder } from '../../data/iconOrientation.js';
-import {
-  buildHeatRaster,
-  heatGridForSpotSize,
-} from '../../data/firmsHeatRaster.js';
+import { buildHeatRaster } from '../../data/firmsHeatRaster.js';
 import {
   LOD_LEVELS,
   CONTEXT_TOP_N,
+  HANDOFF_FADE,
   HEAT_RASTER,
   HEAT_REBUILD_MS,
 } from './policy.js';
 import { createHeatImagery } from './heatImagery.js';
 
+/** The markers drawn under the far bands' heatmap for the hand-off fade. */
+const HANDOFF_MARKER_LOD = LOD_LEVELS.find((lod) => lod.mode === 'detections');
+
+/** Fade steps: a moving camera rewrites marker colors at most this often. */
+const FADE_STEPS = 32;
+
 export function createRendering({
   layerState,
   services,
@@ -64,14 +68,54 @@ export function createRendering({
       ? components.model.paddedDegreeBounds(viewRect)
       : null;
 
-    if (lod.mode === 'detections') {
-      renderDetections(lod, bounds);
-    } else {
-      renderHeat(lod, bounds);
-    }
+    renderBand(lod, bounds);
     return true;
   }
 
+  /**
+   * Draw one band. Markers and heatmap stay built in every band; the
+   * hand-off only fades between them.
+   * @param {Object} lod - Band descriptor.
+   * @param {?Object} bounds - Padded view bounds in degrees, or null.
+   */
+
+  function renderBand(lod, bounds) {
+    prepareHeat(lod.mode === 'heat');
+    if (lod.mode === 'detections') renderDetections(lod, bounds);
+    else renderHeat(lod, bounds);
+    applyHandoffFade(true);
+  }
+
+  const fadeColor = new Cesium.Color();
+
+  /**
+   * Cross-fade between markers and heatmap by camera height (HANDOFF_FADE),
+   * on every rendered frame, so a fast zoom never outruns the throttled band
+   * check. Cheap when nothing changed: one height read and a compare.
+   * @param {boolean} [force] Reapply, e.g. to freshly added markers.
+   */
+
+  function applyHandoffFade(force = false) {
+    const height = components.viewport.cameraHeight();
+    const t = Math.min(
+      1,
+      Math.max(
+        0,
+        (height - HANDOFF_FADE.from) / (HANDOFF_FADE.to - HANDOFF_FADE.from),
+      ),
+    );
+    const heat = Math.round(t * t * (3 - 2 * t) * FADE_STEPS) / FADE_STEPS;
+    if (!force && heat === layerState._handoffHeat) return;
+    layerState._handoffHeat = heat;
+    layerState._heatImagery?.setOpacity(heat);
+    const billboards = layerState._billboards;
+    if (!billboards) return;
+    billboards.show = layerState._enabled && heat < 1;
+    const color = Cesium.Color.WHITE.withAlpha(1 - heat, fadeColor);
+    for (let i = 0; i < billboards.length; i += 1)
+      billboards.get(i).color = color;
+  }
+
   /**
    * 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
@@ -147,28 +191,27 @@ export function createRendering({
     return layerState._heatImagery;
   }
 
-  /** Build the heat raster from the shown set at the chosen spot size and drape it. */
+  /** Build the heat raster from the shown set and drape it. */
 
   function rebuildHeatRaster() {
     clearTimeout(layerState._heatRebuildTimer);
     layerState._heatRebuildTimer = null;
     if (layerState._destroyed) return;
-    layerState._heatRaster = buildHeatRaster(
-      layerState._fires,
-      heatGridForSpotSize(HEAT_RASTER, layerState._spotSize),
-    );
+    layerState._heatRaster = buildHeatRaster(layerState._fires, HEAT_RASTER);
     heatImagery().setRaster(layerState._heatRaster);
   }
 
   /**
-   * Make sure the draped heatmap matches the shown set. The first paint is
-   * immediate; later rebuilds (filter drags, refreshes) trail by
-   * HEAT_REBUILD_MS and keep the previous heatmap on screen meanwhile.
+   * Make sure the draped heatmap matches the shown set. The first paint in a
+   * far band is immediate; other builds (filter drags, refreshes, the
+   * preload under the markers) trail by HEAT_REBUILD_MS and keep the
+   * previous heatmap on screen meanwhile.
+   * @param {boolean} now Build at once when nothing is draped yet.
    */
 
-  function ensureHeatRaster() {
+  function ensureHeatRaster(now) {
     if (layerState._heatRaster) return;
-    if (!heatImagery().hasRaster()) {
+    if (now && !heatImagery().hasRaster()) {
       rebuildHeatRaster();
       return;
     }
@@ -179,10 +222,25 @@ export function createRendering({
     );
   }
 
+  /**
+   * Keep the heatmap draped on the current map stack and current with the
+   * shown set in every band; the hand-off fade decides how much of it shows.
+   * @param {boolean} now The camera is in a far band.
+   */
+
+  function prepareHeat(now) {
+    const imagery = heatImagery();
+    // The map stack may have changed since the last render.
+    imagery.rehome();
+    ensureHeatRaster(now);
+    imagery.setShow(layerState._enabled);
+  }
+
   /**
    * Far bands (global/regional): a Snap Map–style heatmap draped over the
    * globe, transparent where nothing burns, plus the decluttered "N FIRES"
-   * cards from the coarse aggregation. No entities and no sprites are drawn;
+   * cards from the coarse aggregation. The nearest band's markers are kept
+   * built underneath for the hand-off fade and hidden once it completes;
    * cards go through the same screen-space label pipeline as detections
    * (see {@link rebuildAmbientLabels}).
    * @param {Object} lod - Active LOD descriptor.
@@ -190,17 +248,7 @@ export function createRendering({
    */
 
   function renderHeat(lod, bounds) {
-    ensureDetectionCollections();
-    layerState._dataSource.entities.removeAll();
-    if (layerState._billboards) layerState._billboards.removeAll();
-    layerState._pickIndexById.clear();
-    layerState._cullPositions.length = 0;
-
-    const imagery = heatImagery();
-    // The map stack may have changed since the last far render.
-    imagery.rehome();
-    ensureHeatRaster();
-    imagery.setShow(layerState._enabled);
+    paintMarkers(HANDOFF_MARKER_LOD, bounds);
 
     const cells = aggregateFires(lod, bounds);
     layerState._cellCount = cells.length;
@@ -242,10 +290,48 @@ export function createRendering({
    */
 
   function renderDetections(lod, bounds) {
-    layerState._heatImagery?.setShow(false);
+    const markers = paintMarkers(lod, bounds);
+    if (!markers) return;
+    const candidates = markers.map((marker) => marker.fire);
+
+    layerState._cellCount = candidates.length;
+    // FRP-sorted walk: marker order doubles as label priority.
+    layerState._labelCandidates = markers;
+    layerState._labelLodDistance = lod.labelDistance;
+
+    components.cards.rebuildAmbientLabels();
+    components.selection.refreshContextRegistrations(
+      candidates.slice(0, CONTEXT_TOP_N),
+    );
+
+    if (lod.id === 'close') {
+      // Batched (chunked ≤200, sequential, session-cached) DEM warm for the
+      // rendered subset; fires are static so each coarse cell resolves once
+      // ever. Re-render ONLY when a floor actually landed — a failed resolve
+      // reports false, so this chain terminates instead of looping against a
+      // down proxy (the next camera-driven rebuild retries).
+      warmFireAnchorFloors(candidates).then((warmed) => {
+        if (!warmed || !layerState._enabled || !layerState._viewer) return;
+        const currentLod = LOD_LEVELS[layerState._currentLodIndex];
+        if (!currentLod || currentLod.mode !== 'detections') return;
+        renderCurrentLod(true);
+      });
+    }
+  }
+
+  /**
+   * The glow-sprite markers for a detections band: the strongest fires in
+   * view, capped at the band's maxDetections, horizon-culled.
+   * @param {Object} lod - Detections band descriptor.
+   * @param {?Object} bounds - Padded view bounds in degrees, or null.
+   * @returns {?Array<Object>} Label candidates for the fires drawn,
+   *   strongest first; null before the sprite collection exists.
+   */
+
+  function paintMarkers(lod, bounds) {
     ensureDetectionCollections();
     layerState._dataSource.entities.removeAll();
-    if (!layerState._billboards) return;
+    if (!layerState._billboards) return null;
     layerState._billboards.removeAll();
     layerState._pickIndexById.clear();
     layerState._cullPositions.length = 0;
@@ -267,10 +353,7 @@ export function createRendering({
       candidates = layerState._firesByFrp.slice(0, lod.maxDetections);
     }
 
-    layerState._cellCount = candidates.length;
-    layerState._labelCandidates = [];
-    layerState._labelLodDistance = lod.labelDistance;
-
+    const markers = [];
     for (const fire of candidates) {
       const coreSize = components.model.frpPixelSize(fire.frp);
       const position = components.model.firePosition(fire);
@@ -278,6 +361,7 @@ export function createRendering({
       const pickId = `firms-${fire.index}`;
       layerState._pickIndexById.set(pickId, fire);
       layerState._cullPositions.push(cullPosition);
+      markers.push({ position, cullPosition, fire, cell: null });
       layerState._billboards.add({
         id: pickId,
         position,
@@ -289,37 +373,13 @@ export function createRendering({
         horizontalOrigin: Cesium.HorizontalOrigin.CENTER,
         disableDepthTestDistance: Number.POSITIVE_INFINITY,
       });
-      // FRP-sorted walk: candidate order doubles as label priority.
-      layerState._labelCandidates.push({
-        position,
-        cullPosition,
-        fire,
-        cell: null,
-      });
     }
 
     // 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),
-    );
-
-    if (lod.id === 'close') {
-      // Batched (chunked ≤200, sequential, session-cached) DEM warm for the
-      // rendered subset; fires are static so each coarse cell resolves once
-      // ever. Re-render ONLY when a floor actually landed — a failed resolve
-      // reports false, so this chain terminates instead of looping against a
-      // down proxy (the next camera-driven rebuild retries).
-      warmFireAnchorFloors(candidates).then((warmed) => {
-        if (!warmed || !layerState._enabled || !layerState._viewer) return;
-        const currentLod = LOD_LEVELS[layerState._currentLodIndex];
-        if (!currentLod || currentLod.mode !== 'detections') return;
-        renderCurrentLod(true);
-      });
-    }
+    return markers;
   }
 
   function ensureDetectionCollections() {
@@ -385,9 +445,11 @@ export function createRendering({
   }
   return {
     renderCurrentLod,
+    renderBand,
     aggregateFires,
     renderHeat,
     renderDetections,
+    applyHandoffFade,
     ensureDetectionCollections,
     removeDetectionCollections,
     fireHorizonOccluder,

src/layers/firms/state.js

@@ -1,6 +1,5 @@
 import * as Cesium from 'cesium';
 import { DEFAULT_FIRE_FILTER } from '../../data/firmsIntensity.js';
-import { HEAT_SPOT_SIZE_DEFAULT } from '../../data/firmsHeatRaster.js';
 
 export function createFirmsState({ services, config }) {
   const layerState = {};
@@ -70,10 +69,6 @@ export function createFirmsState({ services, config }) {
 
   layerState._filter = { ...DEFAULT_FIRE_FILTER };
 
-  /** Heatmap spot size, percent of the shipped size (firmsHeatRaster.js). */
-
-  layerState._spotSize = HEAT_SPOT_SIZE_DEFAULT;
-
   /** Panel callback: repaint the row controls (counter) after a load. */
 
   layerState._rowControlsListener = null;
@@ -147,6 +142,10 @@ export function createFirmsState({ services, config }) {
 
   layerState._heatRebuildTimer = null;
 
+  /** Last applied hand-off fade (0 markers … 1 heatmap); -1 forces a reapply. */
+
+  layerState._handoffHeat = -1;
+
   /** Imagery adapter (heatImagery.js), created on the first far render. */
 
   layerState._heatImagery = null;

src/layers/firms/viewport.js

@@ -151,6 +151,9 @@ export function createViewport({
         // on screen throughout it — so the horizon pass below must keep running
         // while a fetch is in flight. Only the rebuild is gated on fresh data.
         if (!layerState._enabled) return;
+        // Every frame, ahead of the throttle: a fast zoom crosses the whole
+        // hand-off between two band checks.
+        components.rendering.applyHandoffFade();
         const now = performance.now();
         if (now - layerState._lastLodCheck < LOD_CHECK_MS) return;
         layerState._lastLodCheck = now;

src/share/viewCodec.js

@@ -252,11 +252,7 @@ export const SHARE_VIEW_FLAGS = freezeAll([
  * written explicitly.
  */
 export const SHARE_VIEW_LAYER_OPTION_ABSENT = Object.freeze({
-  'local-firms': Object.freeze({
-    minFrp: 0,
-    confidence: 'all',
-    spotSize: 100,
-  }),
+  'local-firms': Object.freeze({ minFrp: 0, confidence: 'all' }),
   traffic: Object.freeze({ roadMode: null }),
   'weather-lightning': Object.freeze({ opacity: 'strong' }),
   'weather-radar': Object.freeze({ opacity: 'strong' }),

src/ui/layerPanel.js

@@ -470,7 +470,7 @@ export class LayerPanel {
   }
 
   /**
-   * A layer's row chips, one-of-many switch, sliders, color legend, info line
+   * A layer's row chips, one-of-many switch, slider, color legend, info line
    * and ordered list. The block
    * is hidden while the layer is off (or while a dependency owner has
    * surrendered it), so a quiet row stays quiet. Chips and list items are
@@ -496,7 +496,7 @@ export class LayerPanel {
     }));
     const infoText = controls?.info ? String(controls.info) : '';
     const segmented = controls?.segmented || null;
-    const sliders = Array.isArray(controls?.sliders) ? controls.sliders : [];
+    const slider = controls?.slider || null;
     // The info line, once shown, stays in place and hides when empty.
     if (infoText) row.info = true;
     return {
@@ -505,10 +505,10 @@ export class LayerPanel {
         legend.length === 0 &&
         !infoText &&
         !segmented &&
-        sliders.length === 0,
+        !slider,
       chips,
       segmented,
-      sliders,
+      slider,
       legend,
       info: row.info
         ? { text: infoText, title: controls?.infoTitle || '' }
@@ -562,10 +562,13 @@ export class LayerPanel {
   // to params through the live descriptor on every tick.
   _moveSlider(id, sliderId, value, generation = this._generation) {
     if (this._destroyed || this._generation !== generation) return;
-    const slider = this._rowControlsFor(id)?.sliders?.find(
-      (entry) => entry.id === sliderId,
-    );
-    if (!slider || typeof slider.params !== 'function' || !this.isEnabled(id))
+    const slider = this._rowControlsFor(id)?.slider;
+    if (
+      !slider ||
+      slider.id !== sliderId ||
+      typeof slider.params !== 'function' ||
+      !this.isEnabled(id)
+    )
       return;
     this.setLayerParams(id, slider.params(value), { origin: 'user' });
   }

src/ui/layerPanel/LayerRows.vue

@@ -63,10 +63,11 @@ defineProps({
             :segmented="item.controls.segmented"
             :on-select="(optionId) => onChip(item.id, optionId)"
           /><RowSlider
-            v-for="slider in item.controls.sliders || []"
-            :key="slider.id"
-            :slider="slider"
-            :on-input="(value) => onSlider(item.id, slider.id, value)"
+            v-if="item.controls.slider"
+            :slider="item.controls.slider"
+            :on-input="
+              (value) => onSlider(item.id, item.controls.slider.id, value)
+            "
           /><span
             v-for="(entry, index) in item.controls.legend"
             :key="index"

src/ui/layerPanel/layerRows.test.mjs

@@ -66,40 +66,28 @@ const fireRow = (value, active = 'all') => ({
         active: mode === active,
       })),
     },
-    sliders: [
-      {
-        id: 'min-frp',
-        label: 'Fire intensity (FRP)',
-        ariaLabel: 'Minimum fire radiative power, megawatts',
-        valueText: value ? `≥ ${value} MW` : 'All',
-        min: 0,
-        max: 1000,
-        step: 1,
-        value,
-        track: 'linear-gradient(90deg, #9e2a1b, #fff3b0)',
-        ticks: [
-          { at: 0, label: '0' },
-          { at: 0.5, label: '30' },
-        ],
-      },
-      {
-        id: 'heat-spot-size',
-        label: 'Heatmap spot size',
-        ariaLabel: 'Far-zoom heatmap spot size',
-        valueText: '1×',
-        min: 0,
-        max: 1000,
-        value: 333,
-        ticks: [{ at: 1 / 3, label: '1×' }],
-      },
-    ],
+    slider: {
+      id: 'min-frp',
+      label: 'Fire intensity (FRP)',
+      ariaLabel: 'Minimum fire radiative power, megawatts',
+      valueText: value ? `≥ ${value} MW` : 'All',
+      min: 0,
+      max: 1000,
+      step: 1,
+      value,
+      track: 'linear-gradient(90deg, #9e2a1b, #fff3b0)',
+      ticks: [
+        { at: 0, label: '0' },
+        { at: 0.5, label: '30' },
+      ],
+    },
     legend: [],
     info: null,
     list: null,
   },
 });
 
-test('a row switch and sliders render their markup and report choices', () => {
+test('a row switch and slider render their markup and report choices', () => {
   document.body.replaceChildren();
   const container = document.body.appendChild(document.createElement('div'));
   const chips = [];
@@ -127,13 +115,8 @@ test('a row switch and sliders render their markup and report choices', () => {
   segments[1].click();
   assert.deepEqual(chips, [['fires', 'confidence-high']]);
 
-  const blocks = [...container.querySelectorAll('.data-toggle-slider')];
-  assert.deepEqual(
-    blocks.map((entry) => entry.dataset.sliderId),
-    ['min-frp', 'heat-spot-size'],
-    'sliders render in order, after the switch',
-  );
-  const [block, spotBlock] = blocks;
+  const block = container.querySelector('.data-toggle-slider');
+  assert.equal(block.dataset.sliderId, 'min-frp');
   assert.equal(
     block.querySelector('.data-toggle-slider-label').textContent,
     'Fire intensity (FRP)',
@@ -164,18 +147,7 @@ test('a row switch and sliders render their markup and report choices', () => {
 
   input.value = '120';
   input.dispatchEvent(new Event('input', { bubbles: true }));
-  const spotInput = spotBlock.querySelector('input.data-toggle-slider-input');
-  assert.equal(
-    spotInput.getAttribute('aria-label'),
-    'Far-zoom heatmap spot size',
-  );
-  assert.equal(spotInput.style.getPropertyValue('--slider-track'), '');
-  spotInput.value = '700';
-  spotInput.dispatchEvent(new Event('input', { bubbles: true }));
-  assert.deepEqual(moves, [
-    ['fires', 'min-frp', 120],
-    ['fires', 'heat-spot-size', 700],
-  ]);
+  assert.deepEqual(moves, [['fires', 'min-frp', 120]]);
 
   // The refresh that tick triggers keeps the same nodes and updates the text.
   render(h(LayerRows, { items: [fireRow(120, 'high')], ...props }), container);