fix(infrastructure): ground-sample only stem bases the camera sees

scene.sampleHeight reads only surface rendered for the current view. For a
data centre or dam base outside the frustum or over the horizon it read
through the Earth (about -6,344 km over Ashburn on Esri), failed the 9,000 m
check and retried every 2 s indefinitely, one offscreen render per record.
Over Ashburn that held rest frames at 58-589 ms. Unseen bases are now
skipped without being stamped, so each is sampled on the first walk that
sees it, and they no longer arm the retry render.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/data/localGeojson.test.mjs

@@ -90,6 +90,8 @@ async function createRealLocalLayerHarness({
   globalThis.window = { dispatchEvent() {} };
   let sampleHeightImpl = sampleHeight;
   const sampleCalls = { count: 0 };
+  // The camera frustum, reduced to the one answer ground sampling asks of it.
+  let baseVisibility = Cesium.Intersect.INSIDE;
   const overlayHost = {
     setVisible: (...args) => hostCalls.push(['visible', ...args]),
     setEntries: (...args) => hostCalls.push(['entries', ...args]),
@@ -107,7 +109,14 @@ async function createRealLocalLayerHarness({
     },
     camera: {
       positionWC: Cesium.Cartesian3.fromDegrees(-97.695, 30.205, 100_000),
-      frustum: { fov: Math.PI / 3 },
+      directionWC: new Cesium.Cartesian3(),
+      upWC: new Cesium.Cartesian3(),
+      frustum: {
+        fov: Math.PI / 3,
+        computeCullingVolume: () => ({
+          computeVisibility: () => baseVisibility,
+        }),
+      },
       moveEnd,
       flyTo() {},
     },
@@ -151,6 +160,10 @@ async function createRealLocalLayerHarness({
     sampleCalls,
     /** Swap scene.sampleHeight mid-test (e.g. tiles finally arrive). */
     setSampleHeight(next) { sampleHeightImpl = next; },
+    /** Put the feature's base inside (true) or outside the camera frustum. */
+    setBaseInView(inView) {
+      baseVisibility = inView ? Cesium.Intersect.INSIDE : Cesium.Intersect.OUTSIDE;
+    },
     cleanup() {
       if (originalWindow === undefined) delete globalThis.window;
       else globalThis.window = originalWindow;
@@ -736,6 +749,44 @@ test('ground sampling waits for visible globe tiles before caching a height', as
   assert.ok(Math.abs(baseHeightM(env) - 117) < 0.01);
 });
 
+test('an unseen base is not sampled and arms no retry until it is in view', async (t) => {
+  // Out of view the scene has no surface under the base, so the depth sample
+  // would pass through the Earth (about -6,344 km) and fail on every retry.
+  const env = await createRealLocalLayerHarness({
+    sampleHeightSupported: true, sampleHeight: () => 117,
+  });
+  _resetRenderGovernorForTest();
+  const governorScene = { renders: 0, requestRender() { this.renders += 1; } };
+  installRenderGovernor({ scene: governorScene });
+  governorScene.renders = 0; // discard the governor's own install settling frame
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  const clock = installFakeClock(t);
+  t.after(() => {
+    env.layer.destroy(env.viewer);
+    env.cleanup();
+    _resetRenderGovernorForTest();
+  });
+  env.viewer.scene.globe = { show: true, tilesLoaded: true, getHeight: () => 117 };
+  setCameraAltitude(env, 20_000);
+  env.setBaseInView(false);
+  runArmedRetryChain(env, t, clock, 5);
+  assert.equal(env.sampleCalls.count, 0, 'an off-screen base must not be sampled');
+  assert.equal(governorScene.renders, 0, 'an off-screen base must not keep a parked camera rendering');
+  assert.ok(Math.abs(baseHeightM(env)) < 0.01);
+
+  // In the frustum but over the horizon: 50 m up, about 67 km away.
+  env.setBaseInView(true);
+  env.viewer.camera.positionWC = Cesium.Cartesian3.fromDegrees(-97.0, 30.205, 50);
+  runArmedRetryChain(env, t, clock, 5);
+  assert.equal(env.sampleCalls.count, 0, 'a base over the horizon must not be sampled');
+  assert.equal(governorScene.renders, 0);
+
+  setCameraAltitude(env, 20_000);
+  env.preRender.raise();
+  assert.equal(env.sampleCalls.count, 1, 'the base is sampled on the first walk that sees it');
+  assert.ok(Math.abs(baseHeightM(env) - 117) < 0.01);
+});
+
 test('settled terrain refinement lifts an already sampled stem without another GPU sample', async (t) => {
   const env = await createRealLocalLayerHarness({
     sampleHeightSupported: true, sampleHeight: () => 117,

src/data/localGeojsonCore.js

@@ -1000,9 +1000,9 @@ export function createLocalGeoJsonLayer(
             // governor the retry's preRender never arrives on a parked camera
             // and the stem stays at ellipsoid height (buried/floating) until
             // the user happens to move. Schedule the frame the retry needs.
-            // Gated on a sampleable scene and in-range records only, so a far
-            // camera (or a keyless scene) stays fully idle; the distance is
-            // only computed for still-unsampled stems.
+            // Gated on a sampleable scene and in-range, in-view records only,
+            // so a far camera (or a keyless scene) stays fully idle; the
+            // distance is only computed for still-unsampled stems.
             if (
               canSampleGround &&
               !record.groundSampled &&
@@ -1010,7 +1010,8 @@ export function createLocalGeoJsonLayer(
               Cesium.Cartesian3.distance(
                 viewer.camera.positionWC,
                 record.base,
-              ) < GROUND_SAMPLE_MAX_DISTANCE_M
+              ) < GROUND_SAMPLE_MAX_DISTANCE_M &&
+              groundSampleInView(viewer, record)
             ) {
               groundRetryPending = true;
             }
@@ -1130,9 +1131,44 @@ function refreshLocalTerrainFloor(viewer, record) {
   return true;
 }
 
+const groundSampleSphere = new Cesium.BoundingSphere(
+  new Cesium.Cartesian3(),
+  1,
+);
+
+const groundSampleOccluder = new Cesium.EllipsoidalOccluder(
+  Cesium.Ellipsoid.WGS84,
+);
+
+/**
+ * Whether the camera sees the record's base: inside the view frustum and
+ * above the horizon. scene.sampleHeight reads only surface rendered for the
+ * current view, so a sample of an unseen base passes through the Earth (about
+ * -6,344 km near Ashburn on Esri) and fails on every 2 s retry, each one a
+ * full offscreen render: 110 unseen data centres there held the page near 2 s
+ * a frame indefinitely. An unseen base keeps its stem at the unsampled height
+ * and is sampled on the first walk that sees it.
+ */
+function groundSampleInView(viewer, record) {
+  const camera = viewer.camera;
+  const culling = camera.frustum.computeCullingVolume(
+    camera.positionWC,
+    camera.directionWC,
+    camera.upWC,
+  );
+  Cesium.Cartesian3.clone(record.base, groundSampleSphere.center);
+  if (
+    culling.computeVisibility(groundSampleSphere) === Cesium.Intersect.OUTSIDE
+  )
+    return false;
+  groundSampleOccluder.cameraPosition = camera.positionWC;
+  return groundSampleOccluder.isPointVisible(record.base);
+}
+
 function sampleLocalGroundHeight(viewer, record, now) {
   if (record.groundSampled || !viewer.scene.sampleHeightSupported) return false;
   if (now - record.lastGroundSampleMs < GROUND_SAMPLE_RETRY_MS) return false;
+  if (!groundSampleInView(viewer, record)) return false;
   record.lastGroundSampleMs = now;
   const globe = viewer.scene.globe;
   if (globe?.show && globe.tilesLoaded === false) return false;