From 645f0424505c6fb1286db31f3228f427c62c2e85 Mon Sep 17 00:00:00 2001
From: German Khokhlov <ouchlock@gmail.com>
Date: Fri, 16 Oct 2026 20:51:29 +0400
Subject: [PATCH] feat(globe): surface height quality

engine.surface.sampleHeightDetailed(place, { exclude, lod }) answers
{ height, source: 'tiles' | 'terrain', tileSizeM? } (src/globe/surfaceDetail.js).
On Navara tileSizeM is the extent of the tile that answered and
lod 'finest' takes the finest loaded tile, drawn or not; Cesium answers
tiles without a size, else the globe's terrain. acceptedSurfaceHeight()
turns an answer into a height or a miss: tiles larger than
MAX_FLOOR_TILE_SIZE_M (4 km) are too coarse, terrain is not the mesh.

The mesh floor sampler and the ground snap are engine-only now (a viewer
or scene reaches its engine through engineFromViewer, which also registers
the scene) and treat a coarse answer as a miss, as they treat undefined.
Measured on Navara at Austin: while the tiles stream, a 27.9 km tile reads
143.2 m where the ground is 122.5 m (a 1.8 km tile).

`exclude` takes the engine's own mover sets (MoverSet.id): Cesium hides a
set's primitive for the synchronous sample (Cesium matches excluded objects
per billboard, not per collection); Navara's ray only meets tiles.

"sampleHeight undefined in the app on Navara" did not reproduce: the
startup Austin sample is 121.9 m (tile 889 m) on Navara and 122.4 m on
Cesium; one ModelMesh class is patched.

S2 QA (scripts/qa-surface-heights.mjs, 20 places at JFK, SFO, AUS, roofs
and streets): Navara within 2 m of Cesium at 19/20 from 800 m and 18/20
from 15 km with lod 'finest' (gates 18 and 15); offsets per region
-0.21 / +0.4 / +0.1 m; the Empire State roof differs by 39 m (spire
geometry). Navara tile sizes at 800 m: 112-314 m.
---
 scripts/format-scope.json              |   5 +-
 scripts/package-boundaries.json        |   9 +-
 src/data/meshFloorSampler.test.mjs     | 188 +++++++++++++------------
 src/data/trackedModelRegime.test.mjs   |  16 ++-
 src/globe/cesium/createCesiumEngine.js |   5 +-
 src/globe/cesium/engineFromViewer.js   |  18 ++-
 src/globe/cesium/movers.js             |   6 +
 src/globe/cesium/surface.js            |  83 ++++++++---
 src/globe/cesium/surface.test.mjs      |  41 ++++++
 src/globe/contract.js                  |  13 ++
 src/globe/movers.js                    |   5 +-
 src/globe/navara/surface.js            | 103 ++++++++++----
 src/globe/navara/surface.test.mjs      |  40 ++++++
 src/globe/surfaceDetail.js             |  41 ++++++
 src/globe/surfaceDetail.test.mjs       |  36 +++++
 src/globe/testing/contractSuite.mjs    |  64 +++++++++
 src/globe/testing/fakeEngine.js        |  24 ++++
 src/services/groundSnap.js             |  46 +++---
 src/services/groundSnap.test.mjs       |  41 +++++-
 src/services/meshFloorSampler.js       |  95 +++++--------
 20 files changed, 635 insertions(+), 244 deletions(-)
 create mode 100644 src/globe/surfaceDetail.js
 create mode 100644 src/globe/surfaceDetail.test.mjs

diff --git a/scripts/format-scope.json b/scripts/format-scope.json
index 1fc801cff..7d7851f0f 100644
--- a/scripts/format-scope.json
+++ b/scripts/format-scope.json
@@ -1089,5 +1089,8 @@
   "src/globe/follow.js",
   "src/globe/follow.test.mjs",
   "src/globe/cesium/follow.js",
-  "src/globe/cesium/follow.test.mjs"
+  "src/globe/cesium/follow.test.mjs",
+  "src/globe/surfaceDetail.js",
+  "src/globe/surfaceDetail.test.mjs",
+  "scripts/qa-surface-heights.mjs"
 ]
diff --git a/scripts/package-boundaries.json b/scripts/package-boundaries.json
index a4ec90a5d..ebd865555 100644
--- a/scripts/package-boundaries.json
+++ b/scripts/package-boundaries.json
@@ -2563,7 +2563,8 @@
       "src/globe/navara/movers/moverMesh.js",
       "src/globe/navara/movers/pack.js",
       "src/globe/navara/movers/modelMover.js",
-      "src/globe/navara/movers/index.js"
+      "src/globe/navara/movers/index.js",
+      "src/globe/surfaceDetail.js"
     ],
     "external": [
       "hls.js",
@@ -3214,7 +3215,8 @@
       "src/geo/scaleToGeodeticSurface.js",
       "src/geo/check.js",
       "src/geo/debug.js",
-      "src/geo/developerError.js"
+      "src/geo/developerError.js",
+      "src/globe/surfaceDetail.js"
     ],
     "external": [
       "cesium",
@@ -3694,7 +3696,8 @@
       "src/geo/check.js",
       "src/geo/debug.js",
       "src/geo/developerError.js",
-      "src/time/clock.js"
+      "src/time/clock.js",
+      "src/globe/surfaceDetail.js"
     ],
     "external": ["cesium", "egm96-universal", "pbf"]
   },
diff --git a/src/data/meshFloorSampler.test.mjs b/src/data/meshFloorSampler.test.mjs
index 4b9c649dd..f518dac42 100644
--- a/src/data/meshFloorSampler.test.mjs
+++ b/src/data/meshFloorSampler.test.mjs
@@ -4,9 +4,10 @@
 // The sampler's acceptance rule was previously covered only through
 // `reportValidatedMeshFloorCell` directly, which proves the gate but not the
 // decision that feeds it. These tests call `sampleMeshFloorCells` with a fake
-// scene whose `sampleHeight` returns exactly what Cesium can return — a number,
-// `undefined`, NaN, or a throw — and assert that a cell latches if and only if
-// a REAL DEM prior exists and the sample fits its window.
+// globe engine whose surface answers what an engine can answer — a height,
+// `undefined`, NaN, a throw, or a coarse tile — and assert that a cell
+// latches if and only if a REAL DEM prior exists, the answer is fine enough
+// and the sample fits its window.
 //
 // That requirement is the load-bearing one: this round built a tier that kept
 // the reading when no prior existed, and measured it recording a coarse-LOD
@@ -46,90 +47,8 @@ async function seedDem(cell, ellipsoid) {
   }
 }
 
-/** A scene the sampler accepts: low camera, one visible tileset reporting
- *  tilesLoaded, and a `sampleHeight` under the test's control. */
-function fakeScene(sampleHeight, { cameraHeightM = 900, tilesLoaded = true, show = true } = {}) {
-  // instanceof-compatible without running Cesium's constructor; `tilesLoaded` is
-  // a prototype getter, so it has to be shadowed with an own data property.
-  const tileset = Object.create(Cesium.Cesium3DTileset.prototype);
-  Object.defineProperty(tileset, 'tilesLoaded', { value: tilesLoaded, configurable: true });
-  Object.defineProperty(tileset, 'show', { value: show, configurable: true });
-  return {
-    sampleHeight,
-    camera: { positionCartographic: { height: cameraHeightM } },
-    primitives: { length: 1, get: () => tileset },
-  };
-}
-
-function reset() {
-  _clearMeshFloorCellsForTest();
-  setMeshFloorPreferred(true);
-}
-
-test('sampler: a finite sample with NO DEM prior is stored NOWHERE', () => {
-  reset();
-  const cell = nextSite();
-  sampleMeshFloorCells(fakeScene(() => 138.0), [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'nothing may latch without a prior');
-  assert.equal(cachedGroundFloor(cell.lat, cell.lon), null, 'the shared choke point stays clean');
-});
-
-test('sampler: a finite sample WITH a fitting DEM prior latches and becomes the shared floor', async () => {
-  reset();
-  const cell = nextSite();
-  await seedDem(cell, 120.0);
-  const scene = fakeScene(() => 137.0); // +17 m of mesh over bare earth — in window
-  sampleMeshFloorCells(scene, [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 137.0);
-  assert.equal(cachedGroundFloor(cell.lat, cell.lon), 137.0, 'and it is what every consumer reads');
-});
-
-test('sampler: a sample REJECTED against a real prior is stored nowhere', async () => {
-  reset();
-  const cell = nextSite();
-  await seedDem(cell, 120.0);
-  const scene = fakeScene(() => 400.0); // a tower hit — far outside the +80 m window
-  sampleMeshFloorCells(scene, [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null);
-  assert.equal(cachedGroundFloor(cell.lat, cell.lon), 120.0, 'the DEM prior still answers');
-});
-
-test('sampler: undefined, NaN and a throwing probe latch nothing and crash nothing', async () => {
-  reset();
-  const cell = nextSite();
-  await seedDem(cell, 120.0);
-  for (const bad of [() => undefined, () => Number.NaN, () => { throw new Error('mid-teardown'); }]) {
-    sampleMeshFloorCells(fakeScene(bad), [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
-    assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'no negative latch, no throw');
-  }
-  sampleMeshFloorCells(fakeScene(() => 133.0), [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 133.0, 'and a later good sample still lands');
-});
-
-test('sampler: a high camera or unloaded tiles produce no records at all', async () => {
-  reset();
-  const cell = nextSite();
-  await seedDem(cell, 120.0);
-  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
-  sampleMeshFloorCells(fakeScene(() => 138.0, { cameraHeightM: 90_000 }), [cell], opts);
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'coarse LOD under a high camera');
-  sampleMeshFloorCells(fakeScene(() => 138.0, { tilesLoaded: false }), [cell], opts);
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'mid-stream tiles read coarse');
-});
-
-test('sampler: outside the google-3d regime nothing is sampled at all', () => {
-  reset();
-  const cell = nextSite();
-  setMeshFloorPreferred(false);
-  let calls = 0;
-  sampleMeshFloorCells(fakeScene(() => { calls += 1; return 138.0; }), [cell],
-    { viewerLat: cell.lat, viewerLon: cell.lon });
-  assert.equal(calls, 0, 'on a globe stack the DEM IS the rendered surface');
-  setMeshFloorPreferred(true);
-  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null);
-});
-
-// --- On a globe engine (engine.surface / camera.height / maps.photorealActive)
+/** A globe engine the sampler accepts: low camera over the cell, photoreal
+ *  tiles loaded, and a surface under the test's control. */
 
 async function fakeEngineAt(cell, { heightM = 900, tilesLoaded = true, photoreal = true, sample } = {}) {
   const { createFakeEngine } = await import('../globe/testing/fakeEngine.js');
@@ -144,6 +63,74 @@ async function fakeEngineAt(cell, { heightM = 900, tilesLoaded = true, photoreal
   return engine;
 }
 
+function reset() {
+  _clearMeshFloorCellsForTest();
+  setMeshFloorPreferred(true);
+}
+
+test('sampler: a finite sample with NO DEM prior is stored NOWHERE', async () => {
+  reset();
+  const cell = nextSite();
+  sampleMeshFloorCells(await fakeEngineAt(cell, { sample: () => 138.0 }), [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'nothing may latch without a prior');
+  assert.equal(cachedGroundFloor(cell.lat, cell.lon), null, 'the shared choke point stays clean');
+});
+
+test('sampler: a finite sample WITH a fitting DEM prior latches and becomes the shared floor', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  const engine = await fakeEngineAt(cell, { sample: () => 137.0 }); // +17 m of mesh over bare earth — in window
+  sampleMeshFloorCells(engine, [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 137.0);
+  assert.equal(cachedGroundFloor(cell.lat, cell.lon), 137.0, 'and it is what every consumer reads');
+});
+
+test('sampler: a sample REJECTED against a real prior is stored nowhere', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  const engine = await fakeEngineAt(cell, { sample: () => 400.0 }); // a tower hit — far outside the +80 m window
+  sampleMeshFloorCells(engine, [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null);
+  assert.equal(cachedGroundFloor(cell.lat, cell.lon), 120.0, 'the DEM prior still answers');
+});
+
+test('sampler: undefined, NaN and a throwing probe latch nothing and crash nothing', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  for (const bad of [() => undefined, () => Number.NaN, () => { throw new Error('mid-teardown'); }]) {
+    sampleMeshFloorCells(await fakeEngineAt(cell, { sample: bad }), [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
+    assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'no negative latch, no throw');
+  }
+  sampleMeshFloorCells(await fakeEngineAt(cell, { sample: () => 133.0 }), [cell], { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 133.0, 'and a later good sample still lands');
+});
+
+test('sampler: a high camera or unloaded tiles produce no records at all', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  sampleMeshFloorCells(await fakeEngineAt(cell, { sample: () => 138.0, heightM: 90_000 }), [cell], opts);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'coarse LOD under a high camera');
+  sampleMeshFloorCells(await fakeEngineAt(cell, { sample: () => 138.0, tilesLoaded: false }), [cell], opts);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'mid-stream tiles read coarse');
+});
+
+test('sampler: outside the google-3d regime nothing is sampled at all', async () => {
+  reset();
+  const cell = nextSite();
+  setMeshFloorPreferred(false);
+  let calls = 0;
+  sampleMeshFloorCells(await fakeEngineAt(cell, { sample: () => { calls += 1; return 138.0; } }), [cell],
+    { viewerLat: cell.lat, viewerLon: cell.lon });
+  assert.equal(calls, 0, 'on a globe stack the DEM IS the rendered surface');
+  setMeshFloorPreferred(true);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null);
+});
+
 test('sampler on a globe engine: samples engine.surface and latches against the prior', async () => {
   reset();
   const cell = nextSite();
@@ -151,9 +138,30 @@ test('sampler on a globe engine: samples engine.surface and latches against the
   const engine = await fakeEngineAt(cell, { sample: () => 137.0 });
   sampleMeshFloorCells(engine, [cell], { viewerLat: cell.lat, viewerLon: cell.lon, excludeObjects: ['own'] });
   assert.equal(cachedMeshFloor(cell.lat, cell.lon), 137.0);
-  const [call] = engine.fake.callsOf('surface.sampleHeight');
+  const [call] = engine.fake.callsOf('surface.sampleHeightDetailed');
   assert.ok(Math.abs(Cesium.Math.toDegrees(call.args[0].latitude) - cell.lat) < 1e-9);
-  assert.deepEqual(call.args[1], ['own']);
+  assert.deepEqual(call.args[1], { exclude: ['own'], lod: 'visible' });
+});
+
+test('sampler: a coarse tile answer is a miss; a fine one latches', async () => {
+  reset();
+  const cell = nextSite();
+  await seedDem(cell, 120.0);
+  const opts = { viewerLat: cell.lat, viewerLon: cell.lon };
+  // Measured on Navara at Austin while the tiles streamed: a 28 km tile read
+  // 143.2 m where the ground is 122.5 m (a 1.8 km tile).
+  const engine = await fakeEngineAt(cell);
+  engine.fake.script('sampleHeightDetailed', () => ({ height: 143.2, source: 'tiles', tileSizeM: 27_914 }));
+  sampleMeshFloorCells(engine, [cell], opts);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), null, 'coarse: no latch');
+  engine.fake.script('sampleHeightDetailed', () => ({ height: 122.5, source: 'tiles', tileSizeM: 1_797 }));
+  sampleMeshFloorCells(engine, [cell], opts);
+  assert.equal(cachedMeshFloor(cell.lat, cell.lon), 122.5);
+  const terrainOnly = nextSite();
+  await seedDem(terrainOnly, 120.0);
+  engine.fake.script('sampleHeightDetailed', () => ({ height: 121, source: 'terrain' }));
+  sampleMeshFloorCells(engine, [terrainOnly], { viewerLat: terrainOnly.lat, viewerLon: terrainOnly.lon });
+  assert.equal(cachedMeshFloor(terrainOnly.lat, terrainOnly.lon), null, 'terrain is not the mesh');
 });
 
 test('sampler on a globe engine: a high camera, loading tiles or no photoreal tiles sample nothing', async () => {
@@ -164,7 +172,7 @@ test('sampler on a globe engine: a high camera, loading tiles or no photoreal ti
   for (const options of [{ heightM: 90_000 }, { tilesLoaded: false }, { photoreal: false }]) {
     const engine = await fakeEngineAt(cell, { ...options, sample: () => 138.0 });
     sampleMeshFloorCells(engine, [cell], opts);
-    assert.equal(engine.fake.callsOf('surface.sampleHeight').length, 0, JSON.stringify(options));
+    assert.equal(engine.fake.callsOf('surface.sampleHeightDetailed').length, 0, JSON.stringify(options));
   }
   assert.equal(cachedMeshFloor(cell.lat, cell.lon), null);
 });
diff --git a/src/data/trackedModelRegime.test.mjs b/src/data/trackedModelRegime.test.mjs
index 1b02df1d5..32b3cfaf6 100644
--- a/src/data/trackedModelRegime.test.mjs
+++ b/src/data/trackedModelRegime.test.mjs
@@ -26,6 +26,7 @@ import {
   FLEET_MODEL_ALT_CEIL_M,
   TRACKED_MODEL_EXIT_RATIO,
 } from './trackedModelRegime.js';
+import { registerViewerEngine } from '../globe/cesium/engineFromViewer.js';
 import * as Cesium from 'cesium';
 import flightsLayer, {
   _setTrackedFlightRefreshStateForTest,
@@ -155,7 +156,7 @@ if (typeof globalThis.window === 'undefined') {
 /** A viewer stub whose camera altitude the test can move between evaluations. */
 function viewerAtHeight(height, { tilesLoaded = true, sampleHeight = () => undefined } = {}) {
   const tileset = { show: true, tilesLoaded };
-  return {
+  const viewer = {
     camera: {
       positionCartographic: { height },
       positionWC: Cesium.Cartesian3.fromDegrees(-97.71, 30.21, 5000),
@@ -171,6 +172,19 @@ function viewerAtHeight(height, { tilesLoaded = true, sampleHeight = () => undef
     trackedEntity: undefined,
     entities: { remove() {} },
   };
+  // The ground snap samples through the viewer's engine (engineFromViewer):
+  // the engine surface over this stub's tileset and scene.sampleHeight.
+  registerViewerEngine(viewer, {
+    isDestroyed: () => false,
+    surface: {
+      tilesLoaded: () => viewer.tileset.tilesLoaded === true,
+      sampleHeightDetailed(place, { exclude } = {}) {
+        const h = viewer.scene.sampleHeight(place, exclude);
+        return Number.isFinite(h) ? { height: h, source: 'tiles' } : undefined;
+      },
+    },
+  });
+  return viewer;
 }
 
 /** A billboard with a real position, so the tracked-model driver has somewhere
diff --git a/src/globe/cesium/createCesiumEngine.js b/src/globe/cesium/createCesiumEngine.js
index 4e5bce215..ae27c56fd 100644
--- a/src/globe/cesium/createCesiumEngine.js
+++ b/src/globe/cesium/createCesiumEngine.js
@@ -64,7 +64,10 @@ export function createCesiumEngine(viewer, options = {}) {
       ...(options.moverFactories ? { factories: options.moverFactories } : {}),
     })),
     render,
-    surface: createCesiumSurface(viewer),
+    // Mover sets in a surface `exclude` are hidden for the sample.
+    surface: createCesiumSurface(viewer, {
+      engineExclude: (entry) => movers?.primitiveOf(entry) ?? null,
+    }),
     input: createCesiumInput(viewer, { ...options, picker: picker.picker }),
     credits,
     maps: createCesiumMaps(viewer, {
diff --git a/src/globe/cesium/engineFromViewer.js b/src/globe/cesium/engineFromViewer.js
index 98825e4e6..c6ffa8640 100644
--- a/src/globe/cesium/engineFromViewer.js
+++ b/src/globe/cesium/engineFromViewer.js
@@ -13,11 +13,15 @@ const engines = new WeakMap();
  * @returns {() => void} Unregister (only while it is still the registered one).
  */
 export function registerViewerEngine(viewer, engine) {
-  // The viewer's Cesium camera names the same engine, so callers that hold
-  // only viewer.camera (camera sensitivity claims) reach the engine camera.
-  const keys = [viewer, viewer?.camera, viewer?.scene?.camera].filter(
-    (key, index, all) => key != null && all.indexOf(key) === index,
-  );
+  // The viewer's scene and Cesium camera name the same engine, so callers
+  // that hold only viewer.scene (surface samplers) or viewer.camera (camera
+  // sensitivity claims) reach the engine.
+  const keys = [
+    viewer,
+    viewer?.scene,
+    viewer?.camera,
+    viewer?.scene?.camera,
+  ].filter((key, index, all) => key != null && all.indexOf(key) === index);
   for (const key of keys) engines.set(key, engine);
   return () => {
     for (const key of keys)
@@ -26,8 +30,8 @@ export function registerViewerEngine(viewer, engine) {
 }
 
 /**
- * @param {object | null | undefined} viewer A Cesium viewer or its camera,
- *   or an engine (returned as is).
+ * @param {object | null | undefined} viewer A Cesium viewer, its scene or
+ *   camera, or an engine (returned as is).
  * @returns {import('../contract.js').GlobeEngine | null} The registered
  *   engine, or null.
  */
diff --git a/src/globe/cesium/movers.js b/src/globe/cesium/movers.js
index dcd382a15..8e56b5d67 100644
--- a/src/globe/cesium/movers.js
+++ b/src/globe/cesium/movers.js
@@ -307,6 +307,7 @@ export function createCesiumMovers(
     ordered.splice(at, 0, { order: options.order, primitive });
     rootCollection().add(primitive, at);
     return {
+      primitive,
       commit: () => part.commit(store.dirty()),
       destroy() {
         part.destroy();
@@ -321,6 +322,11 @@ export function createCesiumMovers(
   });
   return {
     movers: registry.movers,
+    /** The primitive drawing a live mover set of this engine, or null. */
+    primitiveOf(set) {
+      const entry = set?.id ? registry.sets.get(set.id) : null;
+      return entry && entry.set === set ? entry.part.primitive : null;
+    },
     /** The set and instance a Cesium pick result belongs to, or null. */
     identify(picked) {
       const known = picked?.primitive ? owners.get(picked.primitive) : null;
diff --git a/src/globe/cesium/surface.js b/src/globe/cesium/surface.js
index b44added3..219699f84 100644
--- a/src/globe/cesium/surface.js
+++ b/src/globe/cesium/surface.js
@@ -1,42 +1,93 @@
 // GlobeSurface on a Cesium scene: the rendered-surface queries that
-// services/groundSnap and services/meshFloorSampler make today.
+// services/groundSnap and services/meshFloorSampler make.
+//
+// `exclude` takes the engine's own mover sets (engine.movers) as well as
+// Cesium objects: Cesium's sampleHeight matches excluded objects by the
+// picked primitive, which for a set is each billboard, point or model, so a
+// set is hidden for the sample instead (synchronous: nothing draws in
+// between) and shown again after it.
 
 import { firstVisibleTileset } from '../../services/groundSnap.js';
+import { normalizeSurfaceOptions } from '../surfaceDetail.js';
 import { toGeo3 } from './convert.js';
 
 const finite = (value) => (Number.isFinite(value) ? value : undefined);
 
 /**
  * @param {Cesium.Viewer} viewer
+ * @param {{ engineExclude?: (entry: any) => ({ show: boolean } | null) }} [options]
+ *   `engineExclude` maps an engine object (a mover set) to the Cesium
+ *   primitive that draws it, or null for a Cesium object.
  * @returns {{ surface: import('../contract.js').GlobeSurface, destroy: () => void }}
  */
-export function createCesiumSurface(viewer) {
+export function createCesiumSurface(
+  viewer,
+  { engineExclude = () => null } = {},
+) {
   const { scene } = viewer;
-  const surface = {
-    sampleHeight(cartographic, exclude) {
-      if (!scene.sampleHeightSupported) return undefined;
-      try {
-        // Throws when unsupported (no depth textures); that is a miss.
-        return finite(scene.sampleHeight(cartographic, exclude));
-      } catch {
-        return undefined;
+
+  // Runs `query(nativeExclude)` with the engine objects in `exclude` hidden.
+  function excluding(exclude, query) {
+    if (!exclude?.length) return query(exclude);
+    let native = exclude;
+    const hidden = [];
+    for (const entry of exclude) {
+      const primitive = engineExclude(entry);
+      if (!primitive) continue;
+      if (native === exclude)
+        native = exclude.filter((other) => !engineExclude(other));
+      if (primitive.show) {
+        primitive.show = false;
+        hidden.push(primitive);
       }
+    }
+    try {
+      return query(native);
+    } finally {
+      for (const primitive of hidden) primitive.show = true;
+    }
+  }
+
+  const sampleHeight = (cartographic, exclude) => {
+    if (!scene.sampleHeightSupported) return undefined;
+    try {
+      // Throws when unsupported (no depth textures); that is a miss.
+      return excluding(exclude, (native) =>
+        finite(scene.sampleHeight(cartographic, native)),
+      );
+    } catch {
+      return undefined;
+    }
+  };
+  const terrainHeight = (cartographic) =>
+    scene.globe ? finite(scene.globe.getHeight(cartographic)) : undefined;
+
+  const surface = {
+    sampleHeight,
+    // Cesium samples the tiles it has loaded (lod 'finest' cannot do better
+    // synchronously) and does not say which tile answered.
+    sampleHeightDetailed(cartographic, options) {
+      const { exclude } = normalizeSurfaceOptions(options);
+      const height = sampleHeight(cartographic, exclude);
+      if (height !== undefined) return { height, source: 'tiles' };
+      const terrain = terrainHeight(cartographic);
+      return terrain === undefined
+        ? undefined
+        : { height: terrain, source: 'terrain' };
     },
     get supported() {
       return Boolean(scene.sampleHeightSupported);
     },
-    terrainHeight(cartographic) {
-      return scene.globe
-        ? finite(scene.globe.getHeight(cartographic))
-        : undefined;
-    },
+    terrainHeight,
     get terrainHeightSupported() {
       return Boolean(scene.globe);
     },
     clampToHeight(position, exclude) {
       if (!scene.clampToHeightSupported) return undefined;
       try {
-        return toGeo3(scene.clampToHeight(position, exclude));
+        return excluding(exclude, (native) =>
+          toGeo3(scene.clampToHeight(position, native)),
+        );
       } catch {
         return undefined;
       }
diff --git a/src/globe/cesium/surface.test.mjs b/src/globe/cesium/surface.test.mjs
index 2ff89be20..91df264c4 100644
--- a/src/globe/cesium/surface.test.mjs
+++ b/src/globe/cesium/surface.test.mjs
@@ -84,3 +84,44 @@ test('tilesLoaded follows the first visible tileset, else the shown globe', () =
   tileset.tilesLoaded = true;
   assert.equal(surface.tilesLoaded(), true);
 });
+
+test('sampleHeightDetailed: tiles from sampleHeight, else terrain; no tile size', () => {
+  const { surface, scene } = setup();
+  const place = geo.cartographic.fromDegrees(20, 10, 0);
+  assert.deepEqual(surface.sampleHeightDetailed(place), {
+    height: 42,
+    source: 'tiles',
+  });
+  scene.sampleHeight = () => undefined;
+  assert.deepEqual(surface.sampleHeightDetailed(place, { lod: 'finest' }), {
+    height: 12.5,
+    source: 'terrain',
+  });
+  assert.throws(
+    () => surface.sampleHeightDetailed(place, { lod: 2 }),
+    TypeError,
+  );
+});
+
+test('an engine mover set in exclude is hidden for the sample, native objects pass', () => {
+  const viewer = createFakeViewer();
+  const collection = { show: true };
+  const set = { id: 'flights' };
+  const { surface } = createCesiumSurface(viewer, {
+    engineExclude: (entry) => (entry === set ? collection : null),
+  });
+  const shownDuring = [];
+  viewer.scene.sampleHeight = (position, excluded) => {
+    shownDuring.push(collection.show, excluded);
+    return 30;
+  };
+  const native = { primitive: 1 };
+  const place = geo.cartographic.fromDegrees(20, 10, 0);
+  assert.equal(surface.sampleHeight(place, [set, native]), 30);
+  assert.deepEqual(shownDuring, [false, [native]]);
+  assert.equal(collection.show, true, 'shown again after the sample');
+  shownDuring.length = 0;
+  surface.sampleHeightDetailed(place, { exclude: [set] });
+  assert.deepEqual(shownDuring, [false, []]);
+  assert.equal(collection.show, true);
+});
diff --git a/src/globe/contract.js b/src/globe/contract.js
index c915afd8b..24bbfe709 100644
--- a/src/globe/contract.js
+++ b/src/globe/contract.js
@@ -183,6 +183,12 @@
  * @typedef {object} GlobeSurface
  * @property {(cartographic: Cartographic, exclude?: any[]) => (number | undefined)} sampleHeight
  *   Height of the rendered scene (tiles, models) under a point.
+ * @property {(cartographic: Cartographic, options?: { exclude?: any[], lod?: 'visible' | 'finest' }) => (SurfaceHeight | undefined)} sampleHeightDetailed
+ *   sampleHeight with the answer's quality (src/globe/surfaceDetail.js):
+ *   lod 'visible' (default) answers from the tiles drawn now, 'finest' from
+ *   the finest loaded ones (Navara; Cesium samples what it has loaded).
+ *   Where no tile answers, the terrain. `exclude` takes this engine's mover
+ *   sets as well as engine objects.
  * @property {boolean} supported Whether sampleHeight works.
  * @property {(cartographic: Cartographic) => (number | undefined)} terrainHeight
  *   Height of the terrain/globe surface only (Cesium's globe.getHeight).
@@ -192,6 +198,12 @@
  * @property {boolean} clampToHeightSupported
  * @property {() => boolean} tilesLoaded
  *
+ * @typedef {object} SurfaceHeight
+ * @property {number} height Metres above the ellipsoid.
+ * @property {'tiles' | 'terrain'} source
+ * @property {number} [tileSizeM] The size of the tile that answered
+ *   (Navara): the quality signal; Cesium does not say.
+ *
  * @typedef {object} GlobeRender
  * @property {(reason?: string) => void} request Renders a frame soon in
  *   request mode; `reason` is for diagnostics only.
@@ -585,6 +597,7 @@ const SHAPE = {
   },
   surface: {
     sampleHeight: isFunction,
+    sampleHeightDetailed: isFunction,
     supported: isBoolean,
     terrainHeight: isFunction,
     terrainHeightSupported: isBoolean,
diff --git a/src/globe/movers.js b/src/globe/movers.js
index 468276326..2fc65e009 100644
--- a/src/globe/movers.js
+++ b/src/globe/movers.js
@@ -309,12 +309,14 @@ export function createMoverStore(options) {
  * destroy. commit() hands the engine the changed range and cleans the store;
  * a destroyed set refuses every call but destroy().
  */
-export function createMoverSet(store, { commit, destroy }) {
+export function createMoverSet(store, { id, commit, destroy }) {
   let destroyed = false;
   const alive = () => {
     if (destroyed) throw new Error('Mover set was destroyed');
   };
   return {
+    // The set's id (createSet's `id`): surface exclusion and picks name it.
+    id,
     set(index, fields) {
       alive();
       store.set(index, fields);
@@ -359,6 +361,7 @@ export function createMoverRegistry(build) {
       const part = build(options, store);
       const entry = { options, store, part, set: null };
       entry.set = createMoverSet(store, {
+        id: options.id,
         commit: () => part.commit(),
         destroy: () => {
           sets.delete(options.id);
diff --git a/src/globe/navara/surface.js b/src/globe/navara/surface.js
index 67fb3bcbc..fa2fa54d7 100644
--- a/src/globe/navara/surface.js
+++ b/src/globe/navara/surface.js
@@ -20,6 +20,7 @@ import {
   Vector3,
 } from 'three';
 import * as geo from '../../geo/index.js';
+import { normalizeSurfaceOptions } from '../surfaceDetail.js';
 
 const { cartesian3, cartographic, math } = geo;
 const WGS84 = geo.ellipsoid.WGS84;
@@ -62,17 +63,22 @@ const hasPositions = (object) =>
   object.isMesh && Boolean(object.geometry?.attributes?.position?.array);
 
 // The meshes with CPU positions under `object`, minus `exclude`, into
-// `out`; with `shownOnly`, only through visible objects.
-function collectMeshes(object, exclude, shownOnly, out) {
+// `out`; with `shownOnly`, only through visible objects. `roots` (when
+// given) gets the tile root of each mesh, at the same index.
+function collectMeshes(object, exclude, shownOnly, out, roots, root) {
   if (exclude.has(object) || (shownOnly && !object.visible)) return;
-  if (hasPositions(object)) out.push(object);
+  if (hasPositions(object)) {
+    out.push(object);
+    roots?.push(root);
+  }
   const children = object.children;
   for (let i = 0; i < children.length; i++)
-    collectMeshes(children[i], exclude, shownOnly, out);
+    collectMeshes(children[i], exclude, shownOnly, out, roots, root);
 }
 
 // Reused between calls (sampleHeight runs per frame in the ground floor).
 const shownMeshes = [];
+const shownRoots = [];
 const tileMeshesScratch = [];
 
 // Nearest hit along worldRay with one mesh, in metres. Not Mesh.raycast: that
@@ -114,25 +120,32 @@ function meshHitDistance(mesh, far) {
 }
 
 // Nearest hit over meshes, tried in the order the ray enters their bounding
-// spheres; stops once the next sphere starts below the best hit.
-function nearestHit(meshes, ray) {
+// spheres; stops once the next sphere starts below the best hit. Returns
+// the distance and the tile root (from `roots`) of the mesh hit.
+function nearestHit(meshes, roots, ray) {
   worldRay.origin.set(ray.origin.x, ray.origin.y, ray.origin.z);
   worldRay.direction.set(ray.direction.x, ray.direction.y, ray.direction.z);
   const candidates = [];
-  for (const mesh of meshes) {
+  for (let i = 0; i < meshes.length; i++) {
+    const mesh = meshes[i];
     const geometry = mesh.geometry;
     if (!geometry.boundingSphere) geometry.computeBoundingSphere();
     sphere.copy(geometry.boundingSphere).applyMatrix4(mesh.matrixWorld);
     if (!worldRay.intersectSphere(sphere, entry)) continue;
-    candidates.push([worldRay.origin.distanceTo(entry), mesh]);
+    candidates.push([worldRay.origin.distanceTo(entry), i]);
   }
   candidates.sort((x, y) => x[0] - y[0]);
   let nearest = Infinity;
-  for (const [enter, mesh] of candidates) {
+  let root = null;
+  for (const [enter, i] of candidates) {
     if (enter > nearest) break;
-    nearest = Math.min(nearest, meshHitDistance(mesh, ray.far));
+    const distance = meshHitDistance(meshes[i], ray.far);
+    if (distance < nearest) {
+      nearest = distance;
+      root = roots[i];
+    }
   }
-  return nearest;
+  return { distance: nearest, root };
 }
 
 // A tile's extent: the bounding sphere around all its meshes, in
@@ -167,20 +180,22 @@ const NO_EXCLUDE = new Set();
 // the top one among them. Tiles the ray passes are tried finest first, and
 // coarser ones stop being tried once a hit sets the limit, so the coarse
 // parents' triangles are never walked.
+// With `includeShown` (lod 'finest') the shown tiles take part too.
 const hiddenTiles = [];
-function finestHiddenHit(roots, exclude, ray) {
+function finestHiddenHit(roots, exclude, ray, includeShown = false) {
   worldRay.origin.set(ray.origin.x, ray.origin.y, ray.origin.z);
   worldRay.direction.set(ray.direction.x, ray.direction.y, ray.direction.z);
   hiddenTiles.length = 0;
   for (let i = 0; i < roots.length; i++) {
     const root = roots[i];
-    if (root.visible || exclude.has(root)) continue;
+    if ((root.visible && !includeShown) || exclude.has(root)) continue;
     const extent = tileExtent(root);
     if (extent && worldRay.intersectsSphere(extent)) hiddenTiles.push(root);
   }
   hiddenTiles.sort((x, y) => extents.get(x).radius - extents.get(y).radius);
   let limit = Infinity;
   let nearest = Infinity;
+  let answered = null;
   for (const root of hiddenTiles) {
     const radius = extents.get(root).radius;
     if (radius > limit) break;
@@ -191,12 +206,21 @@ function finestHiddenHit(roots, exclude, ray) {
       hit = Math.min(hit, meshHitDistance(mesh, ray.far));
     if (!Number.isFinite(hit)) continue;
     if (limit === Infinity) limit = 1.5 * radius;
-    nearest = Math.min(nearest, hit);
+    if (hit < nearest) {
+      nearest = hit;
+      answered = root;
+    }
   }
   hiddenTiles.length = 0;
-  return nearest;
+  return { distance: nearest, root: answered };
 }
 
+// The size of a tile that answered: its extent's diameter.
+const tileSizeOf = (root) => {
+  const extent = root ? tileExtent(root) : null;
+  return extent ? 2 * extent.radius : undefined;
+};
+
 /**
  * @param {{ sampleTerrainHeight: (place: { lat: number, lng: number }) => number | undefined }} view
  * @param {{
@@ -221,25 +245,48 @@ export function createNavaraSurface(view, hooks) {
     });
     return Number.isFinite(height) ? height : undefined;
   };
-  const sampleHeight = (place, exclude) => {
-    if (!supported) return undefined;
+  const terrainDetail = (place) => {
+    const height = terrainHeight(place);
+    return height === undefined ? undefined : { height, source: 'terrain' };
+  };
+  const sampleHeightDetailed = (place, options) => {
+    const { exclude, lod } = normalizeSurfaceOptions(options);
+    if (!supported) return terrainDetail(place);
     const ray = surfaceRay(place);
     const roots = hooks.tileRoots();
-    const excluded = exclude ? new Set(exclude) : NO_EXCLUDE;
-    // The tiles on screen first; where they do not reach (the ground under
-    // a camera looking ahead is outside the frustum), the hidden ones.
-    shownMeshes.length = 0;
-    for (let i = 0; i < roots.length; i++)
-      collectMeshes(roots[i], excluded, true, shownMeshes);
-    let distance = nearestHit(shownMeshes, ray);
-    shownMeshes.length = 0;
-    if (!Number.isFinite(distance))
-      distance = finestHiddenHit(roots, excluded, ray);
-    return heightAlongRay(ray, distance) ?? terrainHeight(place);
+    const excluded = exclude.length ? new Set(exclude) : NO_EXCLUDE;
+    let hit = { distance: Infinity, root: null };
+    if (lod === 'visible') {
+      // The tiles on screen first; where they do not reach (the ground
+      // under a camera looking ahead is outside the frustum), the hidden
+      // ones.
+      shownMeshes.length = 0;
+      shownRoots.length = 0;
+      for (let i = 0; i < roots.length; i++)
+        collectMeshes(
+          roots[i],
+          excluded,
+          true,
+          shownMeshes,
+          shownRoots,
+          roots[i],
+        );
+      hit = nearestHit(shownMeshes, shownRoots, ray);
+      shownMeshes.length = 0;
+      shownRoots.length = 0;
+    }
+    if (!Number.isFinite(hit.distance))
+      hit = finestHiddenHit(roots, excluded, ray, lod === 'finest');
+    const height = heightAlongRay(ray, hit.distance);
+    if (height === undefined) return terrainDetail(place);
+    return { height, source: 'tiles', tileSizeM: tileSizeOf(hit.root) };
   };
+  const sampleHeight = (place, exclude) =>
+    sampleHeightDetailed(place, exclude ? { exclude } : undefined)?.height;
   return {
     surface: {
       sampleHeight,
+      sampleHeightDetailed,
       supported,
       terrainHeight,
       terrainHeightSupported: true,
diff --git a/src/globe/navara/surface.test.mjs b/src/globe/navara/surface.test.mjs
index ffefb80a9..8b40f4f0c 100644
--- a/src/globe/navara/surface.test.mjs
+++ b/src/globe/navara/surface.test.mjs
@@ -215,3 +215,43 @@ test('among hidden tiles the finest tile wins by its extent, not by a small mesh
     'the fine tile',
   );
 });
+
+test('sampleHeightDetailed names the source and the size of the answering tile', () => {
+  // A shown coarse tile (600 m wide, 3 m high) over a hidden fine one.
+  const fine = tileAt(10, 45, 40);
+  const coarse = tileAt(10, 45, 43, 300);
+  fine.tile.visible = false;
+  const { surface } = setup({
+    tiles: [coarse.tile, fine.tile],
+    terrain: () => 7,
+  });
+  const place = cartographic.fromDegrees(10, 45, 0);
+  const shown = surface.sampleHeightDetailed(place);
+  assert.equal(shown.source, 'tiles');
+  near(shown.height, 43, 0.05, 'the shown tile');
+  near(shown.tileSizeM, 600 * Math.SQRT2, 1, 'its size');
+  const finest = surface.sampleHeightDetailed(place, { lod: 'finest' });
+  near(finest.height, 40, 0.05, 'the finest loaded tile');
+  near(finest.tileSizeM, 200 * Math.SQRT2, 1, 'its size');
+  assert.deepEqual(
+    surface.sampleHeightDetailed(place, { exclude: [coarse.tile, fine.tile] }),
+    { height: 7, source: 'terrain' },
+  );
+  assert.throws(
+    () => surface.sampleHeightDetailed(place, { lod: 'best' }),
+    TypeError,
+  );
+  const bare = setup({ tiles: [] }).surface;
+  assert.equal(bare.sampleHeightDetailed(place), undefined);
+});
+
+test('a hidden tile answer carries its size too', () => {
+  const fine = tileAt(10, 45, 40);
+  fine.tile.visible = false;
+  const { surface } = setup({ tiles: [fine.tile] });
+  const detail = surface.sampleHeightDetailed(
+    cartographic.fromDegrees(10, 45, 0),
+  );
+  near(detail.height, 40, 0.05, 'hidden fine');
+  near(detail.tileSizeM, 200 * Math.SQRT2, 1, 'size');
+});
diff --git a/src/globe/surfaceDetail.js b/src/globe/surfaceDetail.js
new file mode 100644
index 000000000..5901e02d9
--- /dev/null
+++ b/src/globe/surfaceDetail.js
@@ -0,0 +1,41 @@
+// engine.surface.sampleHeightDetailed, the engine-neutral part: its options
+// and the quality rule callers apply to an answer. An answer is
+// { height, source: 'tiles' | 'terrain', tileSizeM? }: `tileSizeM` is the
+// size of the tile that answered (Navara; Cesium does not say), the quality
+// signal, since a coarse tile's surface can sit tens of metres off the
+// ground (a 20 m error measured at Austin while the tiles were streaming).
+
+const LODS = new Set(['visible', 'finest']);
+
+/**
+ * @param {{ exclude?: any[], lod?: 'visible' | 'finest' }} [options]
+ *   `exclude`: mover sets (or their ids), lines, or engine objects the ray
+ *   passes through. `lod`: 'visible' answers from the tiles drawn now (where
+ *   they miss, the finest loaded ones); 'finest' from the finest loaded
+ *   tiles, drawn or not.
+ */
+export function normalizeSurfaceOptions(options = {}) {
+  const exclude = options.exclude ?? [];
+  if (!Array.isArray(exclude))
+    throw new TypeError('surface exclude must be an array');
+  const lod = options.lod ?? 'visible';
+  if (!LODS.has(lod))
+    throw new TypeError(`surface lod must be 'visible' or 'finest': ${lod}`);
+  return { exclude, lod };
+}
+
+/**
+ * The height to use from a detailed answer, or undefined (a miss): tiles
+ * larger than `maxTileSizeM` are too coarse, and terrain counts only with
+ * `terrain: true`.
+ */
+export function acceptedSurfaceHeight(
+  detail,
+  { maxTileSizeM = Infinity, terrain = false } = {},
+) {
+  if (!detail || !Number.isFinite(detail.height)) return undefined;
+  if (detail.source === 'terrain') return terrain ? detail.height : undefined;
+  if (Number.isFinite(detail.tileSizeM) && detail.tileSizeM > maxTileSizeM)
+    return undefined;
+  return detail.height;
+}
diff --git a/src/globe/surfaceDetail.test.mjs b/src/globe/surfaceDetail.test.mjs
new file mode 100644
index 000000000..02924af79
--- /dev/null
+++ b/src/globe/surfaceDetail.test.mjs
@@ -0,0 +1,36 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  acceptedSurfaceHeight,
+  normalizeSurfaceOptions,
+} from './surfaceDetail.js';
+
+test('surface options: exclude list and lod visible (default) or finest', () => {
+  assert.deepEqual(normalizeSurfaceOptions(), { exclude: [], lod: 'visible' });
+  const set = { id: 'flights' };
+  assert.deepEqual(normalizeSurfaceOptions({ exclude: [set], lod: 'finest' }), {
+    exclude: [set],
+    lod: 'finest',
+  });
+  assert.throws(() => normalizeSurfaceOptions({ lod: 'best' }), TypeError);
+  assert.throws(() => normalizeSurfaceOptions({ exclude: 'x' }), TypeError);
+});
+
+test('a coarse tile answer is a miss; terrain only when asked for', () => {
+  const fine = { height: 122.5, source: 'tiles', tileSizeM: 180 };
+  const coarse = { height: 143.2, source: 'tiles', tileSizeM: 5200 };
+  const cesium = { height: 122.4, source: 'tiles' };
+  const terrain = { height: 120, source: 'terrain' };
+  const limit = { maxTileSizeM: 1000 };
+  assert.equal(acceptedSurfaceHeight(fine, limit), 122.5);
+  assert.equal(acceptedSurfaceHeight(coarse, limit), undefined);
+  assert.equal(acceptedSurfaceHeight(coarse), 143.2, 'no limit: kept');
+  assert.equal(acceptedSurfaceHeight(cesium, limit), 122.4, 'no size: kept');
+  assert.equal(acceptedSurfaceHeight(terrain, limit), undefined);
+  assert.equal(acceptedSurfaceHeight(terrain, { terrain: true }), 120);
+  assert.equal(acceptedSurfaceHeight(undefined), undefined);
+  assert.equal(
+    acceptedSurfaceHeight({ height: NaN, source: 'tiles' }),
+    undefined,
+  );
+});
diff --git a/src/globe/testing/contractSuite.mjs b/src/globe/testing/contractSuite.mjs
index 744597719..f595669d9 100644
--- a/src/globe/testing/contractSuite.mjs
+++ b/src/globe/testing/contractSuite.mjs
@@ -1475,6 +1475,70 @@ export function createContractSuite(
         );
       },
     ],
+    [
+      'surface.sampleHeightDetailed: source, tile size, lod and mover-set exclusion',
+      async () => {
+        const place = cartographic.fromDegrees(20, 10, 0);
+        const shape = (detail, label) => {
+          if (detail === undefined) return;
+          ensure(Number.isFinite(detail.height), `${label}: height`);
+          ensure(
+            detail.source === 'tiles' || detail.source === 'terrain',
+            `${label}: source ${detail.source}`,
+          );
+          ensure(
+            detail.tileSizeM === undefined ||
+              (detail.source === 'tiles' && detail.tileSizeM > 0),
+            `${label}: tileSizeM ${detail.tileSizeM}`,
+          );
+        };
+        const visible = engine.surface.sampleHeightDetailed(place);
+        shape(visible, 'visible');
+        shape(
+          engine.surface.sampleHeightDetailed(place, { lod: 'finest' }),
+          'finest',
+        );
+        if (visible?.source === 'tiles')
+          near(
+            engine.surface.sampleHeight(place),
+            visible.height,
+            1e-6,
+            'sampleHeight and the detailed tiles answer',
+          );
+        let rejected = null;
+        try {
+          engine.surface.sampleHeightDetailed(place, { lod: 'best' });
+        } catch (error) {
+          rejected = error;
+        }
+        ensure(rejected instanceof TypeError, 'an unknown lod was accepted');
+        // A mover set in exclude: the sample works and the set stays.
+        const set = engine.movers.createSet({
+          id: 'contract-surface-exclude',
+          kind: 'point',
+          capacity: 1,
+          point: { sizePx: 8 },
+        });
+        try {
+          set.set(0, { position: cartesian3.fromDegrees(20, 10, 50) });
+          set.setCount(1);
+          set.commit();
+          shape(
+            engine.surface.sampleHeightDetailed(place, { exclude: [set] }),
+            'excluding a set',
+          );
+          ensure(set.id === 'contract-surface-exclude', 'the set has no id');
+          ensure(
+            engine.movers
+              .list()
+              .some(({ id }) => id === 'contract-surface-exclude'),
+            'the excluded set is gone',
+          );
+        } finally {
+          set.destroy();
+        }
+      },
+    ],
     [
       'surface: flags, tilesLoaded, sampleHeight, terrainHeight and clampToHeight shapes',
       async () => {
diff --git a/src/globe/testing/fakeEngine.js b/src/globe/testing/fakeEngine.js
index d21b54d48..8477bf438 100644
--- a/src/globe/testing/fakeEngine.js
+++ b/src/globe/testing/fakeEngine.js
@@ -31,6 +31,7 @@ import { createLineRegistry } from '../lines.js';
 import { createMoverRegistry } from '../movers.js';
 import { createCpuPicker } from '../cpuPicks.js';
 import { createFollowController } from '../follow.js';
+import { normalizeSurfaceOptions } from '../surfaceDetail.js';
 
 const { cartesian2, cartesian3, cartographic, ellipsoid, math, matrix4 } = geo;
 const WGS84 = ellipsoid.WGS84;
@@ -55,6 +56,7 @@ const SCRIPTABLE = new Set([
   'pickEllipsoid',
   'viewRectangle',
   'sampleHeight',
+  'sampleHeightDetailed',
   'terrainHeight',
   'clampToHeight',
   'tilesLoaded',
@@ -927,6 +929,28 @@ export function createFakeEngine(options = {}) {
         record('surface.sampleHeight', [position, exclude]);
         return scripted('sampleHeight', [position, exclude], () => undefined);
       },
+      // Scripted as 'sampleHeightDetailed', else from the scripted
+      // sampleHeight (tiles, no size) and terrainHeight.
+      sampleHeightDetailed(position, surfaceOptions) {
+        const { exclude, lod } = normalizeSurfaceOptions(surfaceOptions);
+        record('surface.sampleHeightDetailed', [position, { exclude, lod }]);
+        return scripted(
+          'sampleHeightDetailed',
+          [position, { exclude, lod }],
+          () => {
+            const height = scripted(
+              'sampleHeight',
+              [position, exclude],
+              () => undefined,
+            );
+            if (Number.isFinite(height)) return { height, source: 'tiles' };
+            const terrain = scripted('terrainHeight', [position], () => 0);
+            return Number.isFinite(terrain)
+              ? { height: terrain, source: 'terrain' }
+              : undefined;
+          },
+        );
+      },
       supported: true,
       terrainHeight(position) {
         record('surface.terrainHeight', [position]);
diff --git a/src/services/groundSnap.js b/src/services/groundSnap.js
index be3e9c706..45c4461c6 100644
--- a/src/services/groundSnap.js
+++ b/src/services/groundSnap.js
@@ -47,7 +47,9 @@
  */
 
 import * as geo from '../geo/index.js';
-import { isGlobeEngine } from '../globe/contract.js';
+import { engineFromViewer } from '../globe/cesium/engineFromViewer.js';
+import { acceptedSurfaceHeight } from '../globe/surfaceDetail.js';
+import { MAX_FLOOR_TILE_SIZE_M } from './meshFloorSampler.js';
 
 /** Taxi threshold: a cached snap answers directly for moves up to this far from
  *  the sampled spot (m). Past it the value is demoted to a held last-known and a
@@ -131,24 +133,6 @@ const SAMPLE_BUDGET_PER_WINDOW = 4;
 /** Budget window length (ms). */
 const SAMPLE_WINDOW_MS = 250;
 
-/**
- * True when the active photoreal tileset has finished streaming the tiles in
- * view (cctv.js's projectionTilesReady pattern: first Cesium3DTileset found in
- * scene.primitives, duck-typed via its boolean tilesLoaded). Sampling before
- * that both blows the frame budget on forced synchronous loads and produces
- * misses that would burn retry backoff for nothing. With NO tileset present
- * (OSM fallback) this returns true so the sample path is not permanently
- * blocked — the sample just misses and backs off.
- * @param {Cesium.Viewer} viewer
- * @returns {boolean}
- */
-function _tilesReady(viewer) {
-  const prims = viewer?.scene?.primitives;
-  if (!prims) return false;
-  const tileset = firstVisibleTileset(prims);
-  return tileset ? tileset.tilesLoaded === true : true;
-}
-
 /**
  * The first shown primitive that reports a boolean `tilesLoaded` (a 3D
  * tileset, duck-typed), or null.
@@ -282,21 +266,21 @@ export function createGroundSnap({ groundFloor }) {
    * A contact that HAS resolved once keeps that answer through a resample outage;
    * see `heldSnapM`.
    *
-   * @param {object} target - The globe engine (`engine.surface`: sampleHeight
-   *   and tilesLoaded), or a live Cesium viewer from callers that still hold
-   *   one (scene.sampleHeight and the first visible tileset's tilesLoaded).
+   * @param {object} target - The globe engine (`engine.surface`:
+   *   sampleHeightDetailed and tilesLoaded), or a viewer whose engine is
+   *   registered (engineFromViewer); without one, no sample.
    * @param {string} icao - Cache key (per-layer icao space).
    * @param {Cesium.Cartesian3} pos - Current display position. Cache movement
    *   is measured after projecting this input to the WGS84 ellipsoid, so a
    *   poll-time altitude/datum change cannot invalidate a stationary snap.
    * @param {(() => Array<unknown>)|undefined} getExclusions - Lazily builds the
-   *   scene.sampleHeight objectsToExclude list (own billboards/models/entities —
-   *   the vertical pick ray at a plane's OWN lat/lon lands on its icon/model
-   *   otherwise). Only invoked when a sample actually fires.
+   *   surface `exclude` list (the layer's mover sets, or its own Cesium
+   *   billboards/models/entities — the vertical ray at a plane's OWN lat/lon
+   *   lands on its icon/model otherwise). Only invoked when a sample fires.
    * @returns {number|null}
    */
   function heightFor(target, icao, pos, getExclusions) {
-    const engine = isGlobeEngine(target) ? target : null;
+    const engine = engineFromViewer(target);
     const surfacePos = geo.ellipsoid.WGS84.scaleToGeodeticSurface(
       pos,
       scratchSurfacePos,
@@ -348,7 +332,7 @@ export function createGroundSnap({ groundFloor }) {
       entries.set(icao, next);
       return heldSnapM(next, surfacePos);
     };
-    if (!(engine ? engine.surface.tilesLoaded() : _tilesReady(target)))
+    if (!engine || engine.isDestroyed?.() || !engine.surface.tilesLoaded())
       return miss();
     windowCount += 1;
     let sampled;
@@ -360,9 +344,11 @@ export function createGroundSnap({ groundFloor }) {
       );
       // sampleHeight throws when unsupported (no depth textures) — that's a miss.
       const exclusions = getExclusions ? getExclusions() : undefined;
-      sampled = engine
-        ? engine.surface.sampleHeight(carto, exclusions)
-        : target.scene.sampleHeight(carto, exclusions);
+      // A coarse tile's answer, or only terrain, is a miss.
+      sampled = acceptedSurfaceHeight(
+        engine.surface.sampleHeightDetailed(carto, { exclude: exclusions }),
+        { maxTileSizeM: MAX_FLOOR_TILE_SIZE_M },
+      );
     } catch {
       sampled = undefined;
     }
diff --git a/src/services/groundSnap.test.mjs b/src/services/groundSnap.test.mjs
index e8fbfea77..2cff50c76 100644
--- a/src/services/groundSnap.test.mjs
+++ b/src/services/groundSnap.test.mjs
@@ -23,9 +23,9 @@ test('on a globe engine a snap samples engine.surface once and caches it', () =>
   };
   assert.equal(snap.heightFor(engine, 'a1', KAUS, exclude), 138.5);
   assert.equal(snap.heightFor(engine, 'a1', KAUS, exclude), 138.5);
-  const calls = engine.fake.callsOf('surface.sampleHeight');
+  const calls = engine.fake.callsOf('surface.sampleHeightDetailed');
   assert.equal(calls.length, 1, 'one sample, then the cache');
-  assert.deepEqual(calls[0].args[1], ['own-model']);
+  assert.deepEqual(calls[0].args[1].exclude, ['own-model']);
   assert.equal(exclusions, 1);
   assert.ok(
     Math.abs(geo.math.toDegrees(calls[0].args[0].latitude) - 30.19) < 1e-9,
@@ -39,15 +39,46 @@ test('on a globe engine loading tiles or a miss return null without a sample cac
   engine.fake.script('tilesLoaded', false);
   engine.fake.script('sampleHeight', () => 10);
   assert.equal(snap.heightFor(engine, 'b1', KAUS), null);
-  assert.equal(engine.fake.callsOf('surface.sampleHeight').length, 0);
+  assert.equal(engine.fake.callsOf('surface.sampleHeightDetailed').length, 0);
   engine.fake.script('tilesLoaded', true);
   engine.fake.script('sampleHeight', () => undefined);
   assert.equal(snap.heightFor(engine, 'c1', KAUS), null);
-  assert.equal(engine.fake.callsOf('surface.sampleHeight').length, 1);
+  assert.equal(engine.fake.callsOf('surface.sampleHeightDetailed').length, 1);
   assert.equal(
     snap.heightFor(engine, 'c1', KAUS),
     null,
     'backoff after a miss',
   );
-  assert.equal(engine.fake.callsOf('surface.sampleHeight').length, 1);
+  assert.equal(engine.fake.callsOf('surface.sampleHeightDetailed').length, 1);
+});
+
+test('a coarse tile answer or only terrain is a miss; a viewer reaches its engine', async () => {
+  const { registerViewerEngine } =
+    await import('../globe/cesium/engineFromViewer.js');
+  const snap = createGroundSnap({ groundFloor: groundFloor() });
+  const engine = createFakeEngine();
+  engine.fake.script('sampleHeightDetailed', () => ({
+    height: 143.2,
+    source: 'tiles',
+    tileSizeM: 27_914,
+  }));
+  assert.equal(snap.heightFor(engine, 'd1', KAUS), null, 'coarse');
+  engine.fake.script('sampleHeightDetailed', () => ({
+    height: 121,
+    source: 'terrain',
+  }));
+  assert.equal(snap.heightFor(engine, 'd2', KAUS), null, 'terrain');
+  engine.fake.script('sampleHeightDetailed', () => ({
+    height: 122.5,
+    source: 'tiles',
+    tileSizeM: 1_797,
+  }));
+  const viewer = {};
+  const unregister = registerViewerEngine(viewer, engine);
+  try {
+    assert.equal(snap.heightFor(viewer, 'd3', KAUS), 122.5);
+  } finally {
+    unregister();
+  }
+  assert.equal(snap.heightFor({}, 'd4', KAUS), null, 'no engine: no sample');
 });
diff --git a/src/services/meshFloorSampler.js b/src/services/meshFloorSampler.js
index 9d62891a9..92c76f783 100644
--- a/src/services/meshFloorSampler.js
+++ b/src/services/meshFloorSampler.js
@@ -1,6 +1,12 @@
-import * as Cesium from 'cesium';
 import * as geo from '../geo/index.js';
-import { isGlobeEngine } from '../globe/contract.js';
+import { engineFromViewer } from '../globe/cesium/engineFromViewer.js';
+import { acceptedSurfaceHeight } from '../globe/surfaceDetail.js';
+
+/** Answers from tiles larger than this are too coarse to latch (m): on
+ *  Navara at Austin a 1.8 km tile read the ground (122.5 m) and the 28 km
+ *  tile shown while streaming read 143.2 m. Cesium does not size its
+ *  answers, so its gates are the camera height and tilesLoaded below. */
+export const MAX_FLOOR_TILE_SIZE_M = 4000;
 
 /** Construct an instance-owned meshFloorSampler service with explicit dependencies. */
 export function createMeshFloorSampler({
@@ -50,8 +56,6 @@ export function createMeshFloorSampler({
    *  streamed LOD under a high camera is coarse everywhere, so every probe
    *  would latch junk. */
   const MAX_CAMERA_HEIGHT_M = 25_000;
-  /** @type {Cesium.Cartographic} Scratch for probe coordinates. */
-  const _scratchProbe = new Cesium.Cartographic();
   const _scratchEngineProbe = geo.cartographic.create();
 
   // Regime tracking: mesh cells only apply while the photoreal (google-3d)
@@ -60,28 +64,6 @@ export function createMeshFloorSampler({
   // preference. Module-scope listener: the module only loads in the browser
   // bundle, and the subscription is idempotent for the app's lifetime.
 
-  /**
-   * True when a VISIBLE 3D tileset in the scene reports its streaming queue
-   * drained (tilesLoaded) — the mirror of cctv.js's projectionTilesReady.
-   * Walks top-level primitives only (a handful; once per poll).
-   * @param {Cesium.Scene} scene
-   * @returns {boolean}
-   */
-  function _visibleTilesetLoaded(scene) {
-    try {
-      const prims = scene.primitives;
-      for (let i = 0; i < prims.length; i++) {
-        const p = prims.get(i);
-        if (p instanceof Cesium.Cesium3DTileset && p.show) {
-          return !!p.tilesLoaded;
-        }
-      }
-    } catch {
-      /* mid-teardown */
-    }
-    return false;
-  }
-
   /**
    * Equirectangular distance (km) — same approximation the flights clamp uses.
    */
@@ -99,13 +81,13 @@ export function createMeshFloorSampler({
    * sampleHeight is a CPU-side query against loaded tiles.
    *
    * @param {object|undefined} target - The globe engine (engine.surface,
-   *   camera.height, maps.photorealActive), or the Cesium scene from callers
-   *   that still hold one (skipped when absent/torn down).
+   *   camera.height, maps.photorealActive), or a viewer or scene whose
+   *   engine is registered (engineFromViewer); without one, nothing.
    * @param {Array<{lat: number, lon: number}>} points - Contact/waypoint coords.
    * @param {object} [options]
-   * @param {Array<object>} [options.excludeObjects] - Own billboards/models to
-   *   exclude from the probe (Cesium matches instances/.primitive/.id — pass
-   *   Billboard and Model instances, NOT collections).
+   * @param {Array<object>} [options.excludeObjects] - What the probe passes
+   *   through: the layer's engine mover sets, or (Cesium layers) its own
+   *   Billboard and Model instances.
    * @param {number} [options.viewerLat] @param {number} [options.viewerLon]
    *   Viewer subpoint (computed once by the caller's poll).
    */
@@ -115,25 +97,17 @@ export function createMeshFloorSampler({
     { excludeObjects = [], viewerLat, viewerLon } = {},
   ) {
     if (!meshFloorPreferred()) return;
-    const engine = isGlobeEngine(target) ? target : null;
-    const scene = engine ? null : target;
-    if (engine ? !engine.surface.supported : !scene) return;
-    if (!engine && typeof scene.sampleHeight !== 'function') return;
+    const engine = engineFromViewer(target);
+    if (!engine || engine.isDestroyed?.() || !engine.surface.supported) return;
     if (!Array.isArray(points) || !points.length) return;
     // Round-5 hardening (the CCTV projectionTilesReady lesson, ported late):
     // while tiles are MID-STREAM a probe returns coarse-LOD heights — real
     // numbers, wildly wrong — and the one-shot latch made them permanent.
     // Only sample when the visible Google tileset reports tilesLoaded AND the
     // camera is low enough that the streamed LOD near it is fine-grained.
-    const camH = engine
-      ? engine.camera.height()
-      : scene.camera?.positionCartographic?.height;
+    const camH = engine.camera.height();
     if (!Number.isFinite(camH) || camH > MAX_CAMERA_HEIGHT_M) return;
-    if (
-      !(engine
-        ? engine.maps.photorealActive() && engine.surface.tilesLoaded()
-        : _visibleTilesetLoaded(scene))
-    )
+    if (!(engine.maps.photorealActive() && engine.surface.tilesLoaded()))
       return;
     let sampled = 0;
     const attempted = new Set();
@@ -154,23 +128,19 @@ export function createMeshFloorSampler({
       }
       let height;
       try {
-        if (engine) {
-          const carto = geo.cartographic.fromDegrees(
-            cell.lon,
-            cell.lat,
-            0,
-            _scratchEngineProbe,
-          );
-          height = engine.surface.sampleHeight(carto, excludeObjects);
-        } else {
-          const carto = Cesium.Cartographic.fromDegrees(
-            cell.lon,
-            cell.lat,
-            0,
-            _scratchProbe,
-          );
-          height = scene.sampleHeight(carto, excludeObjects);
-        }
+        const carto = geo.cartographic.fromDegrees(
+          cell.lon,
+          cell.lat,
+          0,
+          _scratchEngineProbe,
+        );
+        // A coarse tile's answer, or only terrain, is a miss (no latch).
+        height = acceptedSurfaceHeight(
+          engine.surface.sampleHeightDetailed(carto, {
+            exclude: excludeObjects,
+          }),
+          { maxTileSizeM: MAX_FLOOR_TILE_SIZE_M },
+        );
         sampled += 1;
       } catch {
         continue; // scene mid-teardown — try again next poll
@@ -223,6 +193,9 @@ export function createMeshFloorSampler({
   return {
     sampleMeshFloorCells,
     cachedGroundFloor,
-    visibleTilesetLoaded: _visibleTilesetLoaded,
+    /** Whether the engine of `target` (a scene or viewer) has its tiles
+     *  loaded (street level's mesh sampler gate). */
+    visibleTilesetLoaded: (target) =>
+      engineFromViewer(target)?.surface.tilesLoaded() ?? false,
   };
 }