Merge branch 'main' into pr/wildlife-sightings

src/app/application.test.mjs

@@ -2,7 +2,20 @@ import test from 'node:test';
 import assert from 'node:assert/strict';
 import { spawnSync } from 'node:child_process';
 import { createApplication } from './application.js';
-import { installTrackpadPinchZoom } from './viewer.js';
+import { KEYHOLE_OUTER_RADIUS } from '../celestialRing.js';
+import * as Cesium from 'cesium';
+import {
+  installFreeLookHeightLimit,
+  installGlobeInViewRecovery,
+  installTrackpadPinchZoom,
+} from './viewer.js';
+import {
+  FREE_LOOK_MAX_HEIGHT_METERS,
+  globeFrameShare,
+  globeOutOfFrame,
+  lookAngleWithinFrame,
+  lookStepLosesGlobe,
+} from '../globeInView.js';
 
 const phases = ['Scene', 'Controls', 'Data', 'Tools'];
 function fixture(overrides = {}) {
@@ -343,3 +356,652 @@ test('trackpad pinch falls back to the original event when relay construction fa
   assert.equal(event.propagationStopped, false);
   assert.equal(f.relayed.length, 0);
 });
+
+function freeLookFixture({ enableLook = true, height = 0 } = {}) {
+  const listeners = new Set();
+  const controller = { enableLook, minimumTrackBallHeight: 7_500_000 };
+  const camera = { positionCartographic: { height } };
+  const viewer = {
+    camera,
+    scene: {
+      screenSpaceCameraController: controller,
+      preUpdate: {
+        addEventListener(listener) {
+          listeners.add(listener);
+          return () => listeners.delete(listener);
+        },
+      },
+    },
+  };
+  const frame = (nextHeight) => {
+    camera.positionCartographic = { height: nextHeight };
+    for (const listener of listeners) listener();
+  };
+  return { viewer, controller, listeners, frame };
+}
+
+test('free look follows camera height and is restored on dispose', () => {
+  const f = freeLookFixture({ height: 500 });
+  const dispose = installFreeLookHeightLimit(f.viewer);
+  assert.equal(f.controller.enableLook, true);
+
+  f.frame(FREE_LOOK_MAX_HEIGHT_METERS + 1);
+  assert.equal(f.controller.enableLook, false);
+  f.frame(FREE_LOOK_MAX_HEIGHT_METERS);
+  assert.equal(f.controller.enableLook, true);
+  f.frame(Number.NaN);
+  assert.equal(f.controller.enableLook, true);
+
+  f.frame(FREE_LOOK_MAX_HEIGHT_METERS * 20);
+  dispose();
+  dispose();
+  assert.equal(f.controller.enableLook, true);
+  assert.equal(f.listeners.size, 0);
+});
+
+test('drags that start on the stars orbit above the free-look height', () => {
+  // Below Cesium's trackball height such a drag turns the camera in place.
+  const f = freeLookFixture({ height: 500 });
+  const dispose = installFreeLookHeightLimit(f.viewer);
+  assert.equal(
+    f.controller.minimumTrackBallHeight,
+    FREE_LOOK_MAX_HEIGHT_METERS,
+  );
+  dispose();
+  assert.equal(f.controller.minimumTrackBallHeight, 7_500_000);
+
+  const lower = freeLookFixture({ height: 500 });
+  lower.controller.minimumTrackBallHeight = 500_000;
+  const disposeLower = installFreeLookHeightLimit(lower.viewer);
+  assert.equal(
+    lower.controller.minimumTrackBallHeight,
+    500_000,
+    'never raised',
+  );
+  disposeLower();
+  assert.equal(lower.controller.minimumTrackBallHeight, 500_000);
+
+  const later = freeLookFixture({ height: 500 });
+  const disposeLater = installFreeLookHeightLimit(later.viewer);
+  later.controller.minimumTrackBallHeight = 2_000_000;
+  disposeLater();
+  assert.equal(
+    later.controller.minimumTrackBallHeight,
+    2_000_000,
+    'dispose keeps a value set after install',
+  );
+});
+
+test('free look keeps a setting other code makes after it is installed', () => {
+  const f = freeLookFixture({ height: 500 });
+  const dispose = installFreeLookHeightLimit(f.viewer);
+  f.controller.enableLook = false;
+  f.frame(10);
+  assert.equal(f.controller.enableLook, false, 'turned off stays off');
+  f.frame(FREE_LOOK_MAX_HEIGHT_METERS * 20);
+  f.frame(10);
+  assert.equal(f.controller.enableLook, false, 'and stays off after orbit');
+  f.controller.enableLook = true;
+  f.frame(10);
+  assert.equal(f.controller.enableLook, true, 'turned back on');
+  f.frame(FREE_LOOK_MAX_HEIGHT_METERS * 20);
+  assert.equal(f.controller.enableLook, false, 'still limited from orbit');
+  f.frame(10);
+  f.controller.enableLook = false;
+  dispose();
+  assert.equal(f.controller.enableLook, false, 'dispose keeps a later setting');
+});
+
+test('free look stays off when the viewer had it disabled', () => {
+  const f = freeLookFixture({ enableLook: false, height: 500 });
+  installFreeLookHeightLimit(f.viewer);
+  f.frame(10);
+  assert.equal(f.controller.enableLook, false);
+});
+
+// A real Cesium camera on the smallest scene its constructor reads, so the
+// frustum test runs on Cesium's own view math rather than a stub.
+function realCamera({ width = 1600, height = 900, mode } = {}) {
+  const scene = {
+    canvas: { clientWidth: width, clientHeight: height },
+    drawingBufferWidth: width,
+    drawingBufferHeight: height,
+    mapProjection: new Cesium.GeographicProjection(),
+    mode: mode ?? Cesium.SceneMode.SCENE3D,
+    pixelRatio: 1,
+    ellipsoid: Cesium.Ellipsoid.WGS84,
+    mapMode2D: Cesium.MapMode2D.INFINITE_SCROLL,
+    tweens: new Cesium.TweenCollection(),
+    renders: 0,
+    requestRender() {
+      this.renders += 1;
+    },
+  };
+  const camera = new Cesium.Camera(scene);
+  camera.frustum.aspectRatio = width / height;
+  return { camera, scene, viewer: { camera, scene } };
+}
+
+function aim(
+  camera,
+  { lon = -94.69, lat = 18.87, alt, heading = 0, pitch, roll = 0 },
+) {
+  camera.setView({
+    destination: Cesium.Cartesian3.fromDegrees(lon, lat, alt),
+    orientation: {
+      heading: Cesium.Math.toRadians(heading),
+      pitch: Cesium.Math.toRadians(pitch),
+      roll: Cesium.Math.toRadians(roll),
+    },
+  });
+}
+
+const reportedStuckView = {
+  alt: 17_996_811,
+  heading: 180,
+  pitch: -42,
+  roll: 180,
+};
+// Oblique poses that still show part of the planet: Director recipe shots
+// (Global Flights Radar, Omniscience Pullback) and a voice tilt from orbit.
+const partialGlobeViews = [
+  { lon: -30, lat: 20, alt: 19_000_000, pitch: -65 },
+  { lon: 2, lat: 46, alt: 8_000_000, pitch: -52 },
+  { lon: 110, lat: 20, alt: 9_500_000, pitch: -66 },
+  { lon: 0, lat: 0, alt: 2_000_000, pitch: -30 },
+];
+
+// Stars and a few pixels of limb, no surface: where a frame limit measured
+// against a sphere of the planet's largest radius used to stop a voice tilt.
+const limbOnlyView = { alt: 18_000_000, pitch: -56.75 };
+
+/**
+ * An oracle independent of the code under test: the share of an 80×45 grid of
+ * Cesium pick rays across the canvas that hit the ellipsoid surface.
+ */
+function surfacePixelShare(camera, width, height, { keyhole = false } = {}) {
+  const radius = (KEYHOLE_OUTER_RADIUS * height) / 2;
+  let hits = 0;
+  let counted = 0;
+  for (let row = 0; row < 45; row += 1) {
+    for (let column = 0; column < 80; column += 1) {
+      const x = ((column + 0.5) * width) / 80;
+      const y = ((row + 0.5) * height) / 45;
+      if (keyhole && Math.hypot(x - width / 2, y - height / 2) > radius)
+        continue;
+      counted += 1;
+      const ray = camera.getPickRay(new Cesium.Cartesian2(x, y));
+      if (Cesium.IntersectionTests.rayEllipsoid(ray, Cesium.Ellipsoid.WGS84))
+        hits += 1;
+    }
+  }
+  return hits / counted;
+}
+
+test('the globe is out of frame only when no surface is on screen', () => {
+  const cases = [
+    [reportedStuckView, 1225, 923, true],
+    [limbOnlyView, 1600, 900, true],
+    [{ alt: 17_996_811, pitch: -90 }, 1225, 923, false],
+    ...partialGlobeViews.map((view) => [view, 1600, 900, false]),
+  ];
+  for (const [view, width, height, out] of cases) {
+    const { camera } = realCamera({ width, height });
+    aim(camera, view);
+    const label = JSON.stringify(view);
+    assert.equal(globeOutOfFrame(camera), out, label);
+    assert.equal(surfacePixelShare(camera, width, height) === 0, out, label);
+    assert.ok(
+      Math.abs(
+        globeFrameShare(camera) - surfacePixelShare(camera, width, height),
+      ) < 0.03,
+      `${label}: the frame share matches the pick-ray oracle`,
+    );
+  }
+});
+
+test('a move that ends with the globe out of frame turns back to nadir', () => {
+  const { camera, scene, viewer } = realCamera({ width: 1225, height: 923 });
+  const dispose = installGlobeInViewRecovery(viewer);
+  aim(camera, reportedStuckView);
+  const position = Cesium.Cartesian3.clone(camera.positionWC);
+  const heading = camera.heading;
+  camera.moveEnd.raiseEvent();
+  assert.ok(Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6));
+  assert.ok(Cesium.Math.equalsEpsilon(camera.heading, heading, 1e-6));
+  assert.ok(
+    Cesium.Cartesian3.equalsEpsilon(camera.positionWC, position, 0, 1e-3),
+  );
+  assert.equal(globeOutOfFrame(camera), false);
+  assert.equal(scene.renders, 1);
+
+  // Looking up near the ground, then zoomed out past the limit.
+  aim(camera, { alt: 3_834_000, pitch: 10 });
+  camera.moveEnd.raiseEvent();
+  assert.ok(Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6));
+
+  // Only the limb on a 16:9 screen still counts as lost.
+  const wide = realCamera({ width: 1600, height: 900 });
+  const disposeWide = installGlobeInViewRecovery(wide.viewer);
+  aim(wide.camera, limbOnlyView);
+  wide.camera.moveEnd.raiseEvent();
+  assert.ok(Cesium.Math.equalsEpsilon(wide.camera.pitch, -Math.PI / 2, 1e-6));
+  disposeWide();
+
+  dispose();
+  dispose();
+  aim(camera, reportedStuckView);
+  camera.moveEnd.raiseEvent();
+  assert.equal(globeOutOfFrame(camera), true, 'disposed recovery is inert');
+});
+
+// True when a moveEnd leaves the camera's view direction as it was.
+function moveEndKeepsView(camera) {
+  const direction = Cesium.Cartesian3.clone(camera.directionWC);
+  camera.moveEnd.raiseEvent();
+  return Cesium.Cartesian3.equalsEpsilon(camera.directionWC, direction, 1e-9);
+}
+
+test('globe recovery leaves partial, low, locked and 2D views alone', () => {
+  for (const view of partialGlobeViews) {
+    const { camera, viewer } = realCamera();
+    installGlobeInViewRecovery(viewer);
+    aim(camera, view);
+    assert.ok(moveEndKeepsView(camera), JSON.stringify(view));
+  }
+
+  const low = realCamera();
+  installGlobeInViewRecovery(low.viewer);
+  aim(low.camera, { alt: 900_000, pitch: 85 });
+  assert.equal(globeOutOfFrame(low.camera), true);
+  assert.ok(moveEndKeepsView(low.camera), 'below the limit');
+
+  // Locked on a point in space, between it and the planet, facing away.
+  const locked = realCamera();
+  installGlobeInViewRecovery(locked.viewer);
+  locked.camera.lookAtTransform(
+    Cesium.Matrix4.fromTranslation(new Cesium.Cartesian3(30_000_000, 0, 0)),
+    new Cesium.Cartesian3(-1_000_000, 0, 0),
+  );
+  assert.equal(globeOutOfFrame(locked.camera), true);
+  assert.ok(moveEndKeepsView(locked.camera), 'locked camera');
+
+  // Tracking an entity that has no position yet keeps an identity transform.
+  const tracked = realCamera();
+  tracked.viewer.trackedEntity = { id: 'pending-fix' };
+  installGlobeInViewRecovery(tracked.viewer);
+  aim(tracked.camera, reportedStuckView);
+  assert.ok(moveEndKeepsView(tracked.camera), 'tracked camera');
+
+  const flat = realCamera({ mode: Cesium.SceneMode.COLUMBUS_VIEW });
+  installGlobeInViewRecovery(flat.viewer);
+  flat.scene.mode = Cesium.SceneMode.SCENE3D;
+  aim(flat.camera, reportedStuckView);
+  flat.scene.mode = Cesium.SceneMode.COLUMBUS_VIEW;
+  assert.ok(moveEndKeepsView(flat.camera), 'Columbus view');
+});
+
+test('the look limit from orbit tolerates grid noise and never reaches zero', () => {
+  const radians = Cesium.Math.toRadians;
+  // About 2% of a 16:9 frame on the planet, below the 10% limit.
+  const sliver = { alt: 18_000_000, pitch: -60 };
+  const { camera } = realCamera();
+  aim(camera, sliver);
+  const start = surfacePixelShare(camera, 1600, 900);
+  assert.ok(start > 0 && start < 0.1, `starts below the limit: ${start}`);
+
+  // Sideways across the sliver: the share wobbles by a cell, the planet stays.
+  assert.equal(lookStepLosesGlobe(camera, 'lookLeft', radians(0.5)), false);
+  const startShare = globeFrameShare(camera);
+  for (let i = 0; i < 20; i += 1) {
+    const step = lookAngleWithinFrame(camera, 'lookLeft', radians(0.25), {
+      startShare,
+    });
+    assert.equal(step, radians(0.25), `sideways step ${i + 1}`);
+    camera.lookLeft(step);
+  }
+  assert.ok(surfacePixelShare(camera, 1600, 900) > 0);
+
+  // Toward the planet is always allowed.
+  aim(camera, sliver);
+  assert.equal(
+    lookAngleWithinFrame(camera, 'lookDown', radians(10)),
+    radians(10),
+  );
+
+  // Away from it stops short of losing it.
+  aim(camera, sliver);
+  const away = lookAngleWithinFrame(camera, 'lookUp', radians(30));
+  assert.ok(away < radians(30));
+  camera.lookUp(away);
+  assert.ok(globeFrameShare(camera) > 0);
+  assert.ok(surfacePixelShare(camera, 1600, 900) > 0);
+});
+
+test('the look limit leaves a view with no surface to the move-end recovery', () => {
+  const { camera } = realCamera({ width: 1225, height: 923 });
+  aim(camera, reportedStuckView);
+  assert.equal(
+    lookAngleWithinFrame(camera, 'lookUp', Cesium.Math.toRadians(5)),
+    Cesium.Math.toRadians(5),
+  );
+});
+
+// Surface only in the corners of a 16:9 frame, all of it outside the scope's
+// keyhole: the full frame shows some planet, the scope shows none.
+const cornerOnlyView = { alt: 18_000_000, pitch: -52, roll: 60 };
+
+test('with a scope keyhole, surface hidden in the masked corners counts as none', () => {
+  const { camera } = realCamera();
+  aim(camera, cornerOnlyView);
+  const keyhole = { keyholeRadius: KEYHOLE_OUTER_RADIUS };
+  assert.ok(surfacePixelShare(camera, 1600, 900) > 0);
+  assert.equal(surfacePixelShare(camera, 1600, 900, { keyhole: true }), 0);
+  assert.equal(globeOutOfFrame(camera), false);
+  assert.equal(globeOutOfFrame(camera, keyhole), true);
+  aim(camera, { alt: 18_000_000, pitch: -90 });
+  assert.ok(
+    Math.abs(
+      globeFrameShare(camera, keyhole) -
+        surfacePixelShare(camera, 1600, 900, { keyhole: true }),
+    ) < 0.03,
+    'the keyhole share matches the pick-ray oracle',
+  );
+});
+
+test('the recovery follows the scope: corner-only views are turned back only behind it', () => {
+  for (const [scopeOn, expectRecovery] of [
+    [true, true],
+    [false, false],
+  ]) {
+    const { camera, viewer } = realCamera();
+    installGlobeInViewRecovery(viewer, {
+      keyholeRadius: () => (scopeOn ? KEYHOLE_OUTER_RADIUS : 0),
+    });
+    aim(camera, cornerOnlyView);
+    camera.moveEnd.raiseEvent();
+    assert.equal(
+      Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6),
+      expectRecovery,
+      `scope ${scopeOn ? 'on' : 'off'}`,
+    );
+  }
+});
+
+test('the recovery leaves a camera flight and an authored scene alone', () => {
+  let playing = true;
+  const { camera, scene, viewer } = realCamera({ width: 1225, height: 923 });
+  scene.camera = camera;
+  scene.screenSpaceCameraController = { enableInputs: true };
+  installGlobeInViewRecovery(viewer, { paused: () => playing });
+  aim(camera, reportedStuckView);
+  camera.moveEnd.raiseEvent();
+  assert.equal(globeOutOfFrame(camera), true, 'a playing scene is left alone');
+  playing = false;
+
+  // A flight that pauses looking away is left alone until it ends.
+  camera.flyTo({
+    destination: Cesium.Cartesian3.fromDegrees(10, 20, 18_000_000),
+    duration: 5,
+  });
+  camera.moveEnd.raiseEvent();
+  assert.equal(globeOutOfFrame(camera), true, 'a flight is left alone');
+  camera.cancelFlight();
+  camera.moveEnd.raiseEvent();
+  assert.ok(Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6));
+});
+
+test('a check a scene or flight defers runs once it ends', () => {
+  for (const viaMoveEnd of [false, true]) {
+    let playing = true;
+    const timers = fakeTimers();
+    const { camera, viewer } = realCamera({ width: 1225, height: 923 });
+    installGlobeInViewRecovery(viewer, {
+      paused: () => playing,
+      ...timers,
+    });
+    aim(camera, reportedStuckView);
+    camera.moveStart.raiseEvent();
+    // A hold on a stars-only shot: quiet, with or without Cesium's moveEnd.
+    for (let i = 0; i < 4; i += 1) timers.tick();
+    if (viaMoveEnd) camera.moveEnd.raiseEvent();
+    // Longer than the settle check's five-minute bound.
+    for (let i = 0; i < 1500; i += 1) timers.tick();
+    assert.equal(globeOutOfFrame(camera), true, 'left alone while it plays');
+    assert.equal(timers.pending(), 1, 'still watching');
+    playing = false;
+    timers.tick();
+    assert.ok(
+      Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6),
+      `recovered once the scene ends (${viaMoveEnd ? 'after moveEnd' : 'no moveEnd'})`,
+    );
+  }
+});
+
+// Holding a drag still for half a second on a view that already showed no
+// surface looked like a settled camera, and the view was turned down under
+// the user's hand.
+test('the recovery waits while a pointer is held on the globe', () => {
+  const timers = fakeTimers();
+  const { camera, scene, viewer } = realCamera({ width: 1225, height: 923 });
+  const document = new EventTarget();
+  scene.canvas = Object.assign(new EventTarget(), {
+    clientWidth: 1225,
+    clientHeight: 923,
+    ownerDocument: document,
+  });
+  const dispose = installGlobeInViewRecovery(viewer, timers);
+  aim(camera, reportedStuckView);
+  scene.canvas.dispatchEvent(new Event('pointerdown'));
+  camera.moveStart.raiseEvent();
+  for (let i = 0; i < 8; i += 1) timers.tick();
+  camera.moveEnd.raiseEvent();
+  for (let i = 0; i < 8; i += 1) timers.tick();
+  assert.equal(globeOutOfFrame(camera), true, 'left alone while held');
+  document.dispatchEvent(new Event('pointerup'));
+  for (let i = 0; i < 3; i += 1) timers.tick();
+  assert.ok(
+    Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6),
+    'recovered once the pointer is released',
+  );
+  dispose();
+  aim(camera, reportedStuckView);
+  scene.canvas.dispatchEvent(new Event('pointerdown'));
+  document.dispatchEvent(new Event('pointerup'));
+  assert.equal(timers.pending(), 0, 'disposed recovery holds no listeners');
+});
+
+/** A held-pointer recovery over a canvas in a document in a window. */
+function heldPointerRecovery() {
+  const timers = fakeTimers();
+  const { camera, scene, viewer } = realCamera({ width: 1225, height: 923 });
+  const window = new EventTarget();
+  const document = Object.assign(new EventTarget(), {
+    defaultView: window,
+    visibilityState: 'visible',
+  });
+  scene.canvas = Object.assign(new EventTarget(), {
+    clientWidth: 1225,
+    clientHeight: 923,
+    ownerDocument: document,
+  });
+  const dispose = installGlobeInViewRecovery(viewer, timers);
+  const pointer = (target, type, pointerId, init = {}) =>
+    target.dispatchEvent(
+      Object.assign(new Event(type), { pointerId, ...init }),
+    );
+  /** Press, move and hold still: the check defers while a pointer is held. */
+  const holdStill = () => {
+    aim(camera, reportedStuckView);
+    camera.moveStart.raiseEvent();
+    for (let i = 0; i < 8; i += 1) timers.tick();
+    camera.moveEnd.raiseEvent();
+    for (let i = 0; i < 8; i += 1) timers.tick();
+  };
+  const settle = () => {
+    for (let i = 0; i < 3; i += 1) timers.tick();
+  };
+  const recovered = () =>
+    Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6);
+  return {
+    camera,
+    document,
+    window,
+    dispose,
+    pointer,
+    holdStill,
+    settle,
+    recovered,
+    canvas: scene.canvas,
+  };
+}
+
+// Releasing one of two fingers cleared the held flag, and the recovery
+// turned the view down under the finger still on the glass.
+test('the recovery waits until every held pointer is released', () => {
+  const h = heldPointerRecovery();
+  h.pointer(h.canvas, 'pointerdown', 1);
+  h.pointer(h.canvas, 'pointerdown', 2);
+  h.holdStill();
+  h.pointer(h.document, 'pointerup', 1);
+  h.settle();
+  assert.equal(h.recovered(), false, 'left alone under the second finger');
+  assert.equal(globeOutOfFrame(h.camera), true);
+  h.pointer(h.document, 'pointercancel', 2);
+  h.settle();
+  assert.equal(h.recovered(), true, 'recovered once both are released');
+  h.dispose();
+});
+
+// A release the page never sees (the pointer let go outside the window)
+// must not hold the recovery off for good.
+for (const [label, lose] of [
+  ['the window loses focus', (h) => h.window.dispatchEvent(new Event('blur'))],
+  [
+    'the page is hidden',
+    (h) => {
+      h.document.visibilityState = 'hidden';
+      h.document.dispatchEvent(new Event('visibilitychange'));
+    },
+  ],
+  [
+    'the canvas loses the pointer capture',
+    (h) => h.pointer(h.canvas, 'lostpointercapture', 1),
+  ],
+  [
+    'the pointer moves with no button down',
+    (h) => h.pointer(h.document, 'pointermove', 1, { buttons: 0 }),
+  ],
+]) {
+  test(`a held pointer whose release is lost stops deferring when ${label}`, () => {
+    const h = heldPointerRecovery();
+    h.pointer(h.canvas, 'pointerdown', 1);
+    h.holdStill();
+    h.pointer(h.document, 'pointermove', 1, { buttons: 1 });
+    h.settle();
+    assert.equal(h.recovered(), false, 'left alone while held');
+    lose(h);
+    h.settle();
+    assert.equal(h.recovered(), true, 'recovered once the hold is let go');
+    h.dispose();
+  });
+}
+
+function fakeTimers() {
+  let next = 1;
+  const pending = new Map();
+  return {
+    setTimeout: (callback) => {
+      const id = next++;
+      pending.set(id, callback);
+      return id;
+    },
+    clearTimeout: (id) => pending.delete(id),
+    pending: () => pending.size,
+    /** Run the earliest pending callback, as 250 ms passing would. */
+    tick() {
+      const [id, callback] = pending.entries().next().value ?? [];
+      if (id === undefined) return false;
+      pending.delete(id);
+      callback();
+      return true;
+    },
+  };
+}
+
+test('a stuck view is recovered once it has held still, without waiting for moveEnd', () => {
+  // At this pose the camera can drift by a rounding error every frame, so
+  // Cesium never sees it stop and never raises moveEnd for it.
+  const timers = fakeTimers();
+  const { camera, viewer } = realCamera({ width: 1225, height: 923 });
+  installGlobeInViewRecovery(viewer, timers);
+  aim(camera, reportedStuckView);
+  camera.moveStart.raiseEvent();
+  timers.tick();
+  assert.equal(globeOutOfFrame(camera), true, 'one quiet sample is not enough');
+  // A rounding-error drift between samples still counts as at rest.
+  camera.lookUp(1e-15);
+  timers.tick();
+  assert.ok(Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6));
+  // Under that drift Cesium raises no new moveStart, so a later move that
+  // ends looking away is caught by the same check.
+  aim(camera, reportedStuckView);
+  timers.tick();
+  timers.tick();
+  assert.equal(globeOutOfFrame(camera), true, 'not yet at rest');
+  timers.tick();
+  assert.ok(Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6));
+  camera.moveEnd.raiseEvent();
+  assert.equal(timers.pending(), 0, 'moveEnd ends the check');
+});
+
+test('the settle check follows a long move and gives up five minutes after the last one', () => {
+  // A drag of half a minute that stops at a stuck pose is still recovered.
+  const long = fakeTimers();
+  const dragged = realCamera({ width: 1225, height: 923 });
+  installGlobeInViewRecovery(dragged.viewer, long);
+  aim(dragged.camera, reportedStuckView);
+  dragged.camera.moveStart.raiseEvent();
+  for (let i = 0; i < 120; i += 1) {
+    dragged.camera.moveLeft(0.01);
+    long.tick();
+  }
+  assert.equal(globeOutOfFrame(dragged.camera), true, 'still moving');
+  while (long.tick());
+  assert.ok(
+    Cesium.Math.equalsEpsilon(dragged.camera.pitch, -Math.PI / 2, 1e-6),
+    'recovered once it stopped',
+  );
+
+  // A camera that keeps moving is followed, and left alone, for as long as it
+  // moves; once it rests the check gives up five minutes later.
+  const timers = fakeTimers();
+  const { camera, viewer } = realCamera({ width: 1225, height: 923 });
+  installGlobeInViewRecovery(viewer, timers);
+  aim(camera, reportedStuckView);
+  camera.moveStart.raiseEvent();
+  for (let i = 0; i < 2000; i += 1) {
+    camera.moveLeft(0.01);
+    timers.tick();
+  }
+  assert.equal(timers.pending(), 1, 'still following after eight minutes');
+  assert.equal(globeOutOfFrame(camera), true, 'a moving camera is left alone');
+  let idleSamples = 0;
+  while (timers.tick()) idleSamples += 1;
+  assert.ok(
+    Cesium.Math.equalsEpsilon(camera.pitch, -Math.PI / 2, 1e-6),
+    'recovered once it stopped',
+  );
+  assert.ok(
+    idleSamples >= 1200 && idleSamples <= 1205,
+    `gave up ${idleSamples} samples after it stopped`,
+  );
+
+  const disposed = fakeTimers();
+  const other = realCamera({ width: 1225, height: 923 });
+  const dispose = installGlobeInViewRecovery(other.viewer, disposed);
+  aim(other.camera, reportedStuckView);
+  other.camera.moveStart.raiseEvent();
+  dispose();
+  assert.equal(disposed.pending(), 0, 'dispose cancels the pending check');
+});

src/app/scene.js

@@ -2,6 +2,7 @@ import { createApplicationOperations } from './operations.js';
 import * as Cesium from 'cesium';
 import {
   createApplicationViewer,
+  installFreeLookHeightLimit,
   installTrackpadPinchZoom,
 } from '../app/viewer.js';
 import { registerDataCredits } from '../data/dataCredits.js';
@@ -58,6 +59,7 @@ export async function createApplicationScene({
     if (!viewer.isDestroyed()) viewer.destroy();
   });
   defer(installTrackpadPinchZoom(viewer));
+  defer(installFreeLookHeightLimit(viewer));
   registerDataCredits(viewer, credits);
   configureCreditKeyboardAccess(document);
   defer(onLocaleChange(() => configureCreditKeyboardAccess(document)));

src/app/tools.js

@@ -8,7 +8,13 @@ import { initImageryBoxTool } from '../ui/imageryBoxTool.js';
 import { createRecentImageryPanel } from '../ui/recentImagery.js';
 import { initGevVoiceCommands } from '../voice/gevRealtime.js';
 import { installViews, isEmbeddedInline } from './embed.js';
-import { installScopeMask, destroyScopeMask } from '../scopeMask.js';
+import {
+  installScopeMask,
+  destroyScopeMask,
+  isScopeMaskEnabled,
+} from '../scopeMask.js';
+import { KEYHOLE_OUTER_RADIUS } from '../celestialRing.js';
+import { installGlobeInViewRecovery } from './viewer.js';
 import { installLayerReleaseTrim } from '../sceneCommandRelease.js';
 import {
   installRenderGovernor,
@@ -44,6 +50,14 @@ export function createApplicationTools({
     .get('bhote-koshi-2026')
     ?.module.attachSceneController(sceneDirector);
   defer(() => sceneDirector.destroy());
+  defer(
+    installGlobeInViewRecovery(viewer, {
+      // The scope mask hides everything outside its keyhole.
+      keyholeRadius: () => (isScopeMaskEnabled() ? KEYHOLE_OUTER_RADIUS : 0),
+      // An authored scene frames its own shots, holds included.
+      paused: () => sceneDirector.running,
+    }),
+  );
   onSceneDirector?.(sceneDirector);
   const annotations = initAnnotations({
     viewer,

src/app/viewer.js

@@ -1,6 +1,11 @@
 import * as Cesium from 'cesium';
 import { applyModelAtmosphereWorkaround } from './atmosphereCompat.js';
 import { StarrySky } from '../sky/starrySky.js';
+import {
+  FREE_LOOK_MAX_HEIGHT_METERS,
+  globeOutOfFrame,
+  isFreeGlobeCamera,
+} from '../globeInView.js';
 
 const PINCH_ZOOM_MULTIPLIER = 8;
 const MAX_PINCH_PIXEL_DELTA = 120;
@@ -103,6 +108,231 @@ export function installTrackpadPinchZoom(
   };
 }
 
+/**
+ * Allow Cesium's free look only below `maxHeight` and return its disposer.
+ * Orbit, tilt and zoom stay available at every height. A value other code
+ * sets later is kept as the one to allow below that height, and restored on
+ * dispose; a `false` written while the camera is above `maxHeight` cannot be
+ * told apart from this limit's own write, so dispose restores the earlier
+ * value then. `enableLook` gates the Shift+drag binding only: below its trackball
+ * height Cesium also turns the camera in place for a drag that starts on the
+ * stars. That height is lowered to `maxHeight` too, so above it such a drag
+ * orbits the globe, as it does above Cesium's own 7,500 km.
+ */
+export function installFreeLookHeightLimit(
+  viewer,
+  maxHeight = FREE_LOOK_MAX_HEIGHT_METERS,
+) {
+  const scene = viewer?.scene;
+  const controller = scene?.screenSpaceCameraController;
+  const camera = viewer?.camera;
+  if (!controller || !camera || !scene?.preUpdate)
+    throw new TypeError('A complete Cesium viewer is required');
+
+  const originalTrackBallHeight = controller.minimumTrackBallHeight;
+  const trackBallHeight = Math.min(originalTrackBallHeight, maxHeight);
+  controller.minimumTrackBallHeight = trackBallHeight;
+  let wanted = controller.enableLook;
+  let written;
+  const sync = () => {
+    if (written !== undefined && controller.enableLook !== written)
+      wanted = controller.enableLook;
+    const height = camera.positionCartographic?.height;
+    written = wanted && !(Number.isFinite(height) && height > maxHeight);
+    controller.enableLook = written;
+  };
+  sync();
+  const removeListener = scene.preUpdate.addEventListener(sync);
+
+  let active = true;
+  return () => {
+    if (!active) return;
+    active = false;
+    removeListener();
+    if (controller.enableLook === written) controller.enableLook = wanted;
+    if (controller.minimumTrackBallHeight === trackBallHeight)
+      controller.minimumTrackBallHeight = originalTrackBallHeight;
+  };
+}
+
+// How often a moving camera is sampled to see whether it has come to rest, how
+// far a pose may drift between samples and still count as at rest, and how
+// long after the camera last moved the check gives up if Cesium never raises
+// moveEnd.
+const SETTLE_SAMPLE_MS = 250;
+const SETTLE_POSITION_TOLERANCE_M = 1e-3;
+const SETTLE_DIRECTION_TOLERANCE = 1e-9;
+const SETTLE_GIVE_UP_MS = 5 * 60_000;
+
+/**
+ * Turn the camera back to the planet when a move ends above `minHeight` with
+ * no surface on screen (`globeOutOfFrame`: limb glow and slivers up to about
+ * one sample cell thick can count as none), and return the disposer. Views with
+ * more surface, such as an oblique orbital shot, are left as they are. This
+ * catches a saved or shared view that looked away, or any other move that ends
+ * looking away from the planet.
+ * Heading and position are kept. Tracked cameras, locked ones (non-identity
+ * transform), a camera flight in progress, a pointer held down on the canvas
+ * (a drag held still), the 2D and Columbus modes, and any time `paused`
+ * returns true (an authored scene playing) are left alone; a check they defer
+ * runs once they end, however long they last.
+ * `keyholeRadius`
+ * returns the radius of the visible circle when a scope mask hides the rest of
+ * the frame (see `globeFrameShare`), or 0; it is read at every check.
+ *
+ * Cesium's `moveEnd` alone is not enough: Cesium compares the camera with the
+ * last frame's to the last rounding error, and at some of these poses the
+ * camera drifts by a rounding error every frame, so Cesium never sees it stop.
+ * So each `moveStart` also starts a check of its own that samples the pose
+ * every 250 ms, with a tolerance for that drift, and once the pose has held
+ * for half a second after moving runs the same recovery. It keeps watching
+ * until Cesium raises `moveEnd`, since under that drift Cesium raises no new
+ * `moveStart` for a later move, and gives up five minutes after the camera
+ * last moved.
+ * `setTimeout` and `clearTimeout` can be injected for tests.
+ */
+export function installGlobeInViewRecovery(
+  viewer,
+  {
+    minHeight = FREE_LOOK_MAX_HEIGHT_METERS,
+    keyholeRadius = () => 0,
+    paused = () => false,
+    setTimeout: schedule = globalThis.setTimeout,
+    clearTimeout: unschedule = globalThis.clearTimeout,
+  } = {},
+) {
+  const scene = viewer?.scene;
+  const camera = viewer?.camera;
+  if (!scene || !camera?.moveEnd || !camera?.moveStart)
+    throw new TypeError('A complete Cesium viewer is required');
+
+  // A pointer held on the globe is a gesture in progress, even when it holds
+  // still for half a second: the check waits until every pointer pressed on
+  // it (each finger of a pinch) is released. A release the page never sees,
+  // outside the window, is taken as given when the window loses focus, the
+  // page is hidden, the canvas loses the pointer's capture, or the pointer
+  // moves with no button down.
+  const canvas = scene.canvas;
+  const releaseTarget = canvas?.ownerDocument ?? canvas;
+  const releaseWindow = canvas?.ownerDocument?.defaultView;
+  const heldPointers = new Set();
+  const onPointerDown = (event) => heldPointers.add(event?.pointerId);
+  const onPointerUp = (event) => heldPointers.delete(event?.pointerId);
+  const onPointerMove = (event) => {
+    if (event?.buttons === 0) heldPointers.delete(event.pointerId);
+  };
+  const releaseAll = () => heldPointers.clear();
+  const onVisibilityChange = () => {
+    if (canvas.ownerDocument.visibilityState === 'hidden') releaseAll();
+  };
+  const listeners = [
+    [canvas, 'pointerdown', onPointerDown],
+    [canvas, 'lostpointercapture', onPointerUp],
+    [releaseTarget, 'pointerup', onPointerUp],
+    [releaseTarget, 'pointercancel', onPointerUp],
+    [releaseTarget, 'pointermove', onPointerMove],
+    [canvas?.ownerDocument, 'visibilitychange', onVisibilityChange],
+    [releaseWindow, 'blur', releaseAll],
+  ];
+  for (const [target, type, listener] of listeners)
+    target?.addEventListener?.(type, listener);
+
+  // Returns false while a flight, a paused scene or a held pointer defers the
+  // check, so the caller can try again once it ends.
+  const recover = () => {
+    if (!isFreeGlobeCamera(viewer)) return true;
+    // Cesium has no public running-flight flag.
+    if (camera._currentFlight || paused() || heldPointers.size > 0)
+      return false;
+    const height = camera.positionCartographic?.height;
+    if (
+      !(height > minHeight) ||
+      !globeOutOfFrame(camera, { keyholeRadius: keyholeRadius() })
+    )
+      return true;
+    camera.setView({
+      orientation: {
+        heading: camera.heading,
+        pitch: -Cesium.Math.PI_OVER_TWO,
+        roll: 0,
+      },
+    });
+    scene.requestRender?.();
+    return true;
+  };
+
+  const lastPosition = new Cesium.Cartesian3();
+  const lastDirection = new Cesium.Cartesian3();
+  let settleTimer = null;
+  let settleElapsed = 0;
+  let restingSamples = 0;
+  let movedSinceCheck = false;
+  const stopSettling = () => {
+    if (settleTimer !== null) unschedule(settleTimer);
+    settleTimer = null;
+  };
+  const sample = () => {
+    settleTimer = null;
+    settleElapsed += SETTLE_SAMPLE_MS;
+    const atRest =
+      Cesium.Cartesian3.equalsEpsilon(
+        camera.positionWC,
+        lastPosition,
+        0,
+        SETTLE_POSITION_TOLERANCE_M,
+      ) &&
+      Cesium.Cartesian3.equalsEpsilon(
+        camera.directionWC,
+        lastDirection,
+        0,
+        SETTLE_DIRECTION_TOLERANCE,
+      );
+    restingSamples = atRest ? restingSamples + 1 : 0;
+    if (!atRest) {
+      movedSinceCheck = true;
+      settleElapsed = 0;
+    }
+    // Two quiet samples in a row after a move: at rest for half a second, as
+    // for moveEnd.
+    if (restingSamples >= 2 && movedSinceCheck) {
+      if (recover()) movedSinceCheck = false;
+      // A flight or a playing scene bounds its own deferral.
+      else settleElapsed = 0;
+    }
+    if (settleElapsed >= SETTLE_GIVE_UP_MS) return;
+    Cesium.Cartesian3.clone(camera.positionWC, lastPosition);
+    Cesium.Cartesian3.clone(camera.directionWC, lastDirection);
+    settleTimer = schedule(sample, SETTLE_SAMPLE_MS);
+  };
+  const startSettling = () => {
+    stopSettling();
+    settleElapsed = 0;
+    restingSamples = 0;
+    movedSinceCheck = true;
+    Cesium.Cartesian3.clone(camera.positionWC, lastPosition);
+    Cesium.Cartesian3.clone(camera.directionWC, lastDirection);
+    settleTimer = schedule(sample, SETTLE_SAMPLE_MS);
+  };
+  const removeMoveEnd = camera.moveEnd.addEventListener(() => {
+    if (recover()) stopSettling();
+    // Deferred: keep sampling so the check runs once the flight or scene ends.
+    else if (settleTimer === null) startSettling();
+  });
+  const removeMoveStart = camera.moveStart.addEventListener(startSettling);
+
+  let active = true;
+  return () => {
+    if (!active) return;
+    active = false;
+    stopSettling();
+    removeMoveEnd();
+    removeMoveStart();
+    for (const [target, type, listener] of listeners)
+      target?.removeEventListener?.(type, listener);
+    heldPointers.clear();
+  };
+}
+
 /** Cesium.Viewer options of the standard globe viewer. */
 export function applicationViewerOptions(creditContainer) {
   return {

src/cameraGlobeRotation.test.mjs

@@ -13,8 +13,16 @@ import {
   moveCamera,
 } from './cameraVerbs.js';
 import { getRenderGovernorDiagnostics } from './renderGovernor.js';
+import {
+  MIN_GLOBE_FRAME_SHARE,
+  globeFrameShare,
+  globeOutOfFrame,
+} from './globeInView.js';
+import { KEYHOLE_OUTER_RADIUS } from './celestialRing.js';
+import { setScopeMaskEnabled } from './scopeMask.js';
 
 const radians = Cesium.Math.toRadians;
+const degrees = Cesium.Math.toDegrees;
 const clone = (value) => Cesium.Cartesian3.clone(value);
 const longitude = (camera) =>
   Cesium.Cartographic.fromCartesian(camera.positionWC).longitude;
@@ -1347,3 +1355,664 @@ test('close-up ultrawide refusal does not offer an unfit reset or move the camer
   samePose(h.camera, before);
   assert.equal(hasRenderHold(), false);
 });
+
+/**
+ * An oracle independent of the code under test: the share of an 80×45 grid of
+ * Cesium pick rays across the canvas that hit the ellipsoid surface. With
+ * `keyhole`, only the pixels inside the scope's visible circle count.
+ */
+function surfacePixelShare(camera, width, height, { keyhole = false } = {}) {
+  const radius = (KEYHOLE_OUTER_RADIUS * height) / 2;
+  let hits = 0;
+  let counted = 0;
+  for (let row = 0; row < 45; row += 1) {
+    for (let column = 0; column < 80; column += 1) {
+      const x = ((column + 0.5) * width) / 80;
+      const y = ((row + 0.5) * height) / 45;
+      if (keyhole && Math.hypot(x - width / 2, y - height / 2) > radius)
+        continue;
+      counted += 1;
+      const ray = camera.getPickRay(new Cesium.Cartesian2(x, y));
+      if (Cesium.IntersectionTests.rayEllipsoid(ray, Cesium.Ellipsoid.WGS84))
+        hits += 1;
+    }
+  }
+  return hits / counted;
+}
+
+/** Run a test with the scope mask on or off, restoring the default after. */
+function withScope(t, enabled) {
+  setScopeMaskEnabled(enabled);
+  t.after(() => setScopeMaskEnabled(true));
+}
+
+// The frame limit is measured on a coarser grid than the oracle.
+const SHARE_SLACK = 0.02;
+// Far-out poses, height in metres and pitch in degrees, where a few tilts up
+// are accepted before the limit refuses the next one.
+const FAR_OUT_POSES = [
+  [35_884_000, -86.26],
+  [35_884_000, -89],
+  [30_000_000, -86],
+  [25_000_000, -80],
+  [40_000_000, -88],
+];
+
+test('voice tilt from orbit stops with the planet still on screen and then says so', (t) => {
+  withScope(t, false); // the whole frame is visible
+  // Slightly off nadir: from straight down a tilt is clamped before it moves.
+  const { camera, finishOnce } = harness(t, {
+    pitch: -80,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  const results = [];
+  for (let i = 0; i < 4; i += 1) {
+    const result = moveCamera({
+      motion: 'tilt',
+      direction: 'up',
+      mode: 'once',
+    });
+    results.push(result);
+    if (result.ok) finishOnce();
+    assert.ok(
+      surfacePixelShare(camera, 1600, 900) >=
+        MIN_GLOBE_FRAME_SHARE - SHARE_SLACK,
+      `after tilt ${i + 1}`,
+    );
+  }
+  // From 18,000 km a 16:9 frame keeps a tenth of its area on the planet down
+  // to about -67°: the first tilt stops there, and later ones are refused.
+  assert.deepEqual(
+    results.map((result) => result.ok),
+    [true, false, false, false],
+  );
+  assert.match(results[1].error, /globe out of view/);
+  assert.ok(camera.pitch > radians(-68.5) && camera.pitch < radians(-66));
+});
+
+// The frame limit judges a tilt by the way its pitch moves, not by the
+// direction word: a tilt down or to a steeper angle turns toward the planet.
+for (const args of [{ direction: 'down' }, { pitchDeg: -80 }]) {
+  test(`a tilt ${JSON.stringify(args)} from the frame limit is judged as the look down it is`, (t) => {
+    withScope(t, false);
+    const { camera, finishOnce } = harness(t, {
+      pitch: -80,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    assert.equal(moveCamera({ motion: 'tilt', direction: 'up' }).ok, true);
+    finishOnce();
+    const atLimit = camera.pitch;
+    const result = moveCamera({ motion: 'tilt', ...args });
+    assert.equal(result.ok, true, result.error);
+    finishOnce();
+    assert.ok(camera.pitch < atLimit - radians(5), 'the tilt turned down');
+  });
+}
+
+for (const args of [{ pitchDeg: -10 }, {}]) {
+  test(`a tilt ${JSON.stringify(args)} up from the frame limit is refused, not reported as done`, (t) => {
+    withScope(t, false);
+    const { camera, finishOnce } = harness(t, {
+      pitch: -80,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    assert.equal(moveCamera({ motion: 'tilt', direction: 'up' }).ok, true);
+    finishOnce();
+    const atLimit = camera.pitch;
+    // A bare tilt means -45°: up from the -67° limit.
+    const result = moveCamera({ motion: 'tilt', ...args });
+    assert.equal(result.ok, false);
+    assert.match(result.error, /globe out of view/);
+    assert.equal(camera.pitch, atLimit);
+  });
+}
+
+// A tilt to an angle, or a bare tilt (-45°), from orbit turns in place like
+// a nudge and must keep the planet in frame the whole way, or the globe
+// recovery would snap the view back down.
+for (const [label, args, options] of [
+  ['a bare tilt', { motion: 'tilt' }, { pitch: -90 }],
+  ['a tilt to -10°', { motion: 'tilt', pitchDeg: -10 }, { pitch: -90 }],
+  [
+    'a continuous tilt up',
+    { motion: 'tilt', direction: 'up', mode: 'continuous' },
+    { pitch: -90 },
+  ],
+  [
+    'a tilt to -5° from 2,000 km',
+    { motion: 'tilt', pitchDeg: -5 },
+    { pitch: -90, height: 2_000_000 },
+  ],
+]) {
+  test(`${label} from top-down never turns the planet out of frame`, (t) => {
+    withScope(t, false);
+    const { camera, tick } = harness(t, {
+      ...options,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    const startPitch = camera.pitch;
+    const result = moveCamera(args);
+    for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) {
+      tick();
+      assert.ok(
+        surfacePixelShare(camera, 1600, 900) >=
+          MIN_GLOBE_FRAME_SHARE - SHARE_SLACK,
+        `frame ${i}: the planet left the frame`,
+      );
+    }
+    assert.equal(getActiveCameraMotion(), null, 'the tilt must stop');
+    assert.equal(globeOutOfFrame(camera), false, 'no snap-back');
+    if (result.ok) assert.ok(camera.pitch > startPitch, 'the tilt moved');
+  });
+}
+
+// The frame limit stops a tilt to an angle short of it: the reply names the
+// angle the camera reaches, not the one asked for (a tilt to -10° from
+// top-down reported -10° and ended at -66.5°).
+for (const [label, args, options] of [
+  ['a bare tilt', { motion: 'tilt' }, { pitch: -90 }],
+  ['a tilt to -10°', { motion: 'tilt', pitchDeg: -10 }, { pitch: -90 }],
+  [
+    'a tilt to -10° from -80°',
+    { motion: 'tilt', pitchDeg: -10 },
+    { pitch: -80 },
+  ],
+  [
+    'a tilt to -5° from 2,000 km',
+    { motion: 'tilt', pitchDeg: -5 },
+    { pitch: -90, height: 2_000_000 },
+  ],
+  // A rolled camera's look turns its pitch by less than the look angle:
+  // reported -25°, ended at -27.3°.
+  [
+    'a tilt to -5° from 2,000 km rolled 30°',
+    { motion: 'tilt', pitchDeg: -5 },
+    { pitch: -70, roll: 30, height: 2_000_000 },
+  ],
+]) {
+  test(`${label} from orbit reports the angle it reaches`, (t) => {
+    withScope(t, false);
+    const { camera, tick } = harness(t, {
+      ...options,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    const result = moveCamera(args);
+    assert.equal(result.ok, true, result.error);
+    for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) tick();
+    assert.equal(getActiveCameraMotion(), null, 'the tilt must stop');
+    const reached = degrees(camera.pitch);
+    assert.ok(
+      Math.abs(reached - result.pitchDeg) < 1,
+      `reported ${result.pitchDeg}°, reached ${reached}°`,
+    );
+    const asked = args.pitchDeg ?? -45;
+    if (Math.abs(reached - asked) >= 1)
+      assert.match(result.note ?? '', /globe out of view/);
+    else assert.equal(result.note, undefined);
+  });
+}
+
+// A continuous tilt promises no angle: it runs until stopped or the frame
+// limit ends it.
+test('a continuous tilt up from orbit claims no angle it may not reach', (t) => {
+  withScope(t, false);
+  const { tick } = harness(t, {
+    pitch: -90,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  const result = moveCamera({
+    motion: 'tilt',
+    direction: 'up',
+    mode: 'continuous',
+  });
+  assert.equal(result.ok, true, result.error);
+  assert.equal('pitchDeg' in result, false);
+  assert.equal(result.mode, 'continuous');
+  for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) tick();
+  assert.equal(getActiveCameraMotion(), null, 'the frame limit ends it');
+});
+
+test('voice turn in place from orbit stops with the planet still on screen', (t) => {
+  withScope(t, false); // the whole frame is visible
+  const { camera, tick } = harness(t, { pitch: -75 });
+  assert.equal(
+    moveCamera({ motion: 'rotate', direction: 'left', mode: 'continuous' }).ok,
+    true,
+  );
+  const heading = camera.heading;
+  for (let i = 0; i < 400 && getActiveCameraMotion(); i += 1) {
+    tick();
+    assert.ok(
+      surfacePixelShare(camera, 1280, 800) >=
+        MIN_GLOBE_FRAME_SHARE - SHARE_SLACK,
+      `tick ${i + 1}`,
+    );
+  }
+  assert.equal(getActiveCameraMotion(), null, 'the turn stops at the limit');
+  assert.notEqual(camera.heading, heading, 'the turn moved before stopping');
+});
+
+test('a long voice turn below the limit keeps the share it started with', (t) => {
+  withScope(t, false); // the whole frame is visible
+  // About 2% of a 16:9 frame on the planet: the limit is that share, less two
+  // grid cells of sampling noise, for the whole motion rather than per step.
+  const { camera, tick } = harness(t, {
+    pitch: -60,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  const start = globeFrameShare(camera);
+  assert.ok(start > 0 && start < MIN_GLOBE_FRAME_SHARE);
+  assert.equal(
+    moveCamera({ motion: 'rotate', direction: 'left', mode: 'continuous' }).ok,
+    true,
+  );
+  for (let i = 0; i < 400 && getActiveCameraMotion(); i += 1) {
+    tick();
+    assert.ok(
+      globeFrameShare(camera) >= start - 2 / (32 * 18) - 1e-9,
+      `tick ${i + 1}`,
+    );
+  }
+  assert.equal(getActiveCameraMotion(), null, 'the turn stops at the limit');
+  assert.ok(surfacePixelShare(camera, 1600, 900) > 0);
+});
+
+test('repeated voice turns from one spot cannot each take a little more', (t) => {
+  withScope(t, false); // the whole frame is visible
+  // About 2% of a 16:9 frame on the planet. Every turn from this position is
+  // measured against the same baseline, so asking again stops being allowed.
+  const { camera, finishOnce, tick } = harness(t, {
+    pitch: -60,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  const start = globeFrameShare(camera);
+  const floor = start - 2 / (32 * 18) - 1e-9;
+  const results = [];
+  for (const mode of ['once', 'once', 'continuous', 'once', 'continuous']) {
+    for (let i = 0; i < 4; i += 1) {
+      const result = moveCamera({ motion: 'rotate', direction: 'left', mode });
+      results.push(result.ok);
+      if (!result.ok) continue;
+      if (mode === 'once') finishOnce();
+      else for (let j = 0; j < 400 && getActiveCameraMotion(); j += 1) tick();
+      assert.ok(globeFrameShare(camera) >= floor, `${mode} turn ${i + 1}`);
+    }
+  }
+  assert.ok(results.includes(false), 'a turn at the limit is refused');
+  assert.equal(results.at(-1), false);
+  assert.ok(surfacePixelShare(camera, 1600, 900) > 0);
+});
+
+test('a voice turn after something else turned the camera starts over', (t) => {
+  withScope(t, false); // the whole frame is visible
+  // The same spot, first framed straight down, then turned to about 2% of the
+  // frame by something other than voice: a turn left is measured from there.
+  const { camera, finishOnce } = harness(t, {
+    pitch: -90,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  assert.equal(
+    moveCamera({ motion: 'rotate', direction: 'left', mode: 'once' }).ok,
+    true,
+  );
+  finishOnce();
+  camera.setView({
+    orientation: { heading: 0, pitch: radians(-60), roll: 0 },
+  });
+  const start = globeFrameShare(camera);
+  assert.ok(start > 0 && start < MIN_GLOBE_FRAME_SHARE);
+  assert.equal(
+    moveCamera({ motion: 'rotate', direction: 'left', mode: 'once' }).ok,
+    true,
+  );
+  finishOnce();
+  assert.ok(globeFrameShare(camera) >= start - 2 / (32 * 18) - 1e-9);
+});
+
+test('nudging the camera between voice turns cannot take the planet below the 1% floor', (t) => {
+  withScope(t, false); // the whole frame is visible
+  // A wheel notch or an orbit drag between requests starts each turn afresh;
+  // the 1% floor still holds, and below it a turn may only keep what it has.
+  for (const [nudge, pitch] of [
+    [(camera) => camera.moveBackward(2), -60],
+    [(camera) => camera.rotateRight(radians(0.2)), -60],
+    [(camera) => camera.moveBackward(2), -58],
+  ]) {
+    const { camera, tick } = harness(t, {
+      pitch,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    const start = globeFrameShare(camera);
+    const floor = Math.min(0.01, start) - 1e-9;
+    for (let i = 0; i < 12; i += 1) {
+      nudge(camera);
+      if (
+        moveCamera({ motion: 'rotate', direction: 'left', mode: 'continuous' })
+          .ok
+      )
+        for (let j = 0; j < 400 && getActiveCameraMotion(); j += 1) tick();
+      assert.ok(
+        globeFrameShare(camera) >= floor,
+        `start ${start}, turn ${i + 1}`,
+      );
+    }
+    assert.ok(surfacePixelShare(camera, 1600, 900) > 0);
+  }
+});
+
+test('after the frame changes size, a voice turn toward the planet is allowed', (t) => {
+  withScope(t, false); // the whole frame is visible
+  // A tilt stops at its limit; then the window widens at the same pose, so the
+  // frame shows less than the carried limit. Toward the planet must still go.
+  const { camera, canvas, viewer, finishOnce } = harness(t, {
+    pitch: -80,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  assert.equal(
+    moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' }).ok,
+    true,
+  );
+  finishOnce();
+  canvas.clientWidth = canvas.width = viewer.scene.drawingBufferWidth = 3200;
+  camera.frustum.aspectRatio = 3200 / 900;
+  const narrowed = globeFrameShare(camera);
+  assert.ok(narrowed < MIN_GLOBE_FRAME_SHARE, `frame now shows ${narrowed}`);
+
+  const down = moveCamera({ motion: 'tilt', direction: 'down', mode: 'once' });
+  assert.equal(down.ok, true, down.error);
+  finishOnce();
+  assert.ok(globeFrameShare(camera) > narrowed);
+  assert.equal(
+    moveCamera({ motion: 'tilt', direction: 'down', mode: 'once' }).ok,
+    true,
+  );
+  finishOnce();
+  const up = moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' });
+  if (up.ok) finishOnce();
+  assert.ok(surfacePixelShare(camera, 3200, 900) > 0);
+});
+
+test('with the scope on, a voice tilt stops while the keyhole still shows the planet', (t) => {
+  withScope(t, true);
+  const { camera, finishOnce } = harness(t, {
+    pitch: -80,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  const results = [];
+  for (let i = 0; i < 4; i += 1) {
+    const result = moveCamera({
+      motion: 'tilt',
+      direction: 'up',
+      mode: 'once',
+    });
+    results.push(result.ok);
+    if (result.ok) finishOnce();
+    assert.ok(
+      surfacePixelShare(camera, 1600, 900, { keyhole: true }) >=
+        MIN_GLOBE_FRAME_SHARE - SHARE_SLACK,
+      `after tilt ${i + 1}`,
+    );
+  }
+  assert.equal(results[0], true);
+  assert.equal(results.at(-1), false, 'a tilt past the limit is refused');
+});
+
+test('with the scope on, a voice turn cannot leave the planet only in the masked corners', (t) => {
+  // An oblique orbit view: turning in place swings the planet toward a corner,
+  // where the full frame still shows it but the scope mask hides it.
+  for (const [height, pitch] of [
+    [5_000_000, -70],
+    [3_000_000, -75],
+    [18_000_000, -80],
+  ]) {
+    withScope(t, true);
+    const { camera, tick } = harness(t, {
+      height,
+      pitch,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    assert.equal(
+      moveCamera({ motion: 'rotate', direction: 'left', mode: 'continuous' })
+        .ok,
+      true,
+    );
+    for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) tick();
+    assert.equal(getActiveCameraMotion(), null, 'the turn stops at the limit');
+    assert.ok(
+      surfacePixelShare(camera, 1600, 900, { keyhole: true }) >=
+        MIN_GLOBE_FRAME_SHARE - SHARE_SLACK,
+      `${height / 1000} km at ${pitch}°`,
+    );
+  }
+});
+
+test('far out, a voice tilt is either refused or really moves, at display frame rates', (t) => {
+  // A small planet disc: its sampled share wobbles as it crosses the grid.
+  // Whatever the limit decides, "done" must mean the camera turned, and some
+  // of these tilts must be accepted for that to be checked at all.
+  let accepted = 0;
+  for (const [height, pitch] of FAR_OUT_POSES) {
+    withScope(t, true);
+    const { camera, tick } = harness(t, {
+      latitude: 45.37,
+      longitudeDeg: -33.33,
+      height,
+      heading: 89.9,
+      pitch,
+      viewportWidth: 1280,
+      viewportHeight: 1024,
+    });
+    for (let i = 0; i < 4; i += 1) {
+      const before = camera.pitch;
+      const result = moveCamera({
+        motion: 'tilt',
+        direction: 'up',
+        mode: 'once',
+      });
+      if (!result.ok) {
+        assert.match(result.error, /zoom in first/);
+        continue;
+      }
+      accepted += 1;
+      for (let j = 0; j < 600 && getActiveCameraMotion(); j += 1) tick(1 / 60);
+      assert.ok(
+        camera.pitch - before > radians(0.5) - 1e-9,
+        `${height / 1000} km at ${pitch}°: tilt ${i + 1} reported done but moved ${Cesium.Math.toDegrees(camera.pitch - before)}°`,
+      );
+    }
+    assert.ok(surfacePixelShare(camera, 1280, 1024, { keyhole: true }) > 0);
+  }
+  assert.ok(accepted > 0, 'no far-out tilt was accepted');
+});
+
+test('a voice turn reported as done turns at least the half degree its check proved', (t) => {
+  // A grazing sliver: the first frame's small step lands in a dip of the
+  // sampled share, which used to stop the turn before it moved at all.
+  for (const scope of [true, false]) {
+    withScope(t, scope);
+    const { camera, tick } = harness(t, {
+      latitude: 20,
+      longitudeDeg: 10,
+      height: 18_000_000,
+      pitch: -58,
+      heading: 37,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    const before = Cesium.Cartesian3.clone(camera.directionWC);
+    const result = moveCamera({
+      motion: 'rotate',
+      direction: 'left',
+      mode: 'once',
+    });
+    if (!result.ok) {
+      assert.match(result.error, /globe out of view/);
+      continue;
+    }
+    for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) tick(1 / 60);
+    const turned = Cesium.Cartesian3.angleBetween(before, camera.directionWC);
+    assert.ok(
+      turned >= radians(0.5) - 1e-9,
+      `scope ${scope ? 'on' : 'off'}: turned ${Cesium.Math.toDegrees(turned)}°`,
+    );
+    assert.ok(surfacePixelShare(camera, 1600, 900, { keyhole: scope }) > 0);
+  }
+});
+
+/** Track an entity below `camera`, locking it into that entity's frame. */
+function trackFrom(viewer, camera) {
+  viewer.trackedEntity = { id: 'high-satellite' };
+  const below = Cesium.Cartesian3.fromDegrees(10, 20, 400_000);
+  camera.lookAtTransform(Cesium.Transforms.eastNorthUpToFixedFrame(below));
+}
+
+test('a voice turn that releases a tracked camera is checked as released', (t) => {
+  // Voice releases the follow camera inside the navigation that runs the
+  // motion, so the request is judged by the pose the release will leave.
+  let accepted = 0;
+  for (const [scope, direction, motion] of [
+    [true, 'up', 'tilt'],
+    [false, 'up', 'tilt'],
+    [false, 'left', 'rotate'],
+  ]) {
+    withScope(t, scope);
+    const { camera, viewer, tick } = harness(t, {
+      latitude: 20,
+      longitudeDeg: 10,
+      height: 18_000_000,
+      pitch: -58,
+      heading: 37,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    trackFrom(viewer, camera);
+    const releaseThenRun = (start) => {
+      viewer.trackedEntity = undefined;
+      camera.lookAtTransform(Cesium.Matrix4.IDENTITY);
+      return start();
+    };
+    const before = Cesium.Cartesian3.clone(camera.directionWC);
+    const result = moveCamera(
+      { motion, direction, mode: 'once' },
+      releaseThenRun,
+    );
+    const label = `${motion} ${direction}, scope ${scope ? 'on' : 'off'}`;
+    if (!result.ok) {
+      assert.match(result.error, /globe out of view/, label);
+      continue;
+    }
+    accepted += 1;
+    for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) tick(1 / 60);
+    const turned = Cesium.Cartesian3.angleBetween(before, camera.directionWC);
+    assert.ok(turned >= radians(0.5) - 1e-9, `${label}: turned ${turned}`);
+    assert.ok(
+      surfacePixelShare(camera, 1600, 900, { keyhole: scope }) > 0,
+      `${label}: the planet stays on screen`,
+    );
+  }
+  assert.ok(accepted > 0, 'no released turn was accepted');
+});
+
+test('a refused voice turn leaves a tracked camera tracking', (t) => {
+  for (const scope of [true, false]) {
+    withScope(t, scope);
+    const { camera, viewer, tick } = harness(t, {
+      pitch: -80,
+      viewportWidth: 1600,
+      viewportHeight: 900,
+    });
+    // Tilt up to the limit untracked, then track from there.
+    for (let i = 0; i < 40; i += 1) {
+      if (!moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' }).ok)
+        break;
+      for (let j = 0; j < 600 && getActiveCameraMotion(); j += 1) tick(1 / 60);
+    }
+    trackFrom(viewer, camera);
+    const tracked = viewer.trackedEntity;
+    const transform = Cesium.Matrix4.clone(camera.transform);
+    let released = false;
+    const result = moveCamera(
+      { motion: 'tilt', direction: 'up', mode: 'once' },
+      (start) => {
+        released = true;
+        viewer.trackedEntity = undefined;
+        camera.lookAtTransform(Cesium.Matrix4.IDENTITY);
+        return start();
+      },
+    );
+    const label = `scope ${scope ? 'on' : 'off'}`;
+    assert.equal(result.ok, false, label);
+    assert.match(result.error, /globe out of view/, label);
+    assert.equal(released, false, label);
+    assert.equal(viewer.trackedEntity, tracked, label);
+    assert.ok(Cesium.Matrix4.equals(camera.transform, transform), label);
+  }
+});
+
+test('a turn proven at one position is checked again after a release moves the camera', (t) => {
+  withScope(t, false);
+  const { camera, tick } = harness(t, {
+    pitch: -80,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  // Tilt up to the limit, then check from 4,000 km closer along the same view
+  // direction, where the next tilt fits; the release moves the camera back.
+  for (let i = 0; i < 40; i += 1) {
+    if (!moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' }).ok)
+      break;
+    for (let j = 0; j < 600 && getActiveCameraMotion(); j += 1) tick(1 / 60);
+  }
+  camera.moveForward(4_000_000);
+  const result = moveCamera(
+    { motion: 'tilt', direction: 'up', mode: 'once' },
+    (start) => {
+      camera.moveBackward(4_000_000);
+      return start();
+    },
+  );
+  assert.equal(result.ok, false);
+  assert.match(result.error, /globe out of view/);
+});
+
+test('the voice frame limit leaves Columbus view alone', (t) => {
+  // At its limit in 3D a further tilt up is refused; the same tilt in Columbus
+  // view is not limited by the frame.
+  withScope(t, false);
+  const { viewer, finishOnce } = harness(t, {
+    pitch: -80,
+    viewportWidth: 1600,
+    viewportHeight: 900,
+  });
+  assert.equal(
+    moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' }).ok,
+    true,
+  );
+  finishOnce();
+  const refused = moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' });
+  assert.match(refused.error || '', /globe out of view/);
+  viewer.scene.mode = Cesium.SceneMode.COLUMBUS_VIEW;
+  const result = moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' });
+  assert.doesNotMatch(result.error || '', /globe out of view/);
+});
+
+test('voice tilt below the free-look height is not limited by the frame', (t) => {
+  const { camera, finishOnce } = harness(t, { height: 500_000, pitch: -60 });
+  const result = moveCamera({ motion: 'tilt', direction: 'up', mode: 'once' });
+  assert.equal(result.ok, true);
+  finishOnce();
+  near(camera.pitch, radians(-45), 1e-6, 'full 15° tilt');
+});

src/cameraVerbs.js

@@ -20,11 +20,19 @@
 
 import * as Cesium from 'cesium';
 import { GLOBE_VIEW } from './locations.js';
+import {
+  globeFrameShare,
+  isFreeGlobeCamera,
+  lookAngleWithinFrame,
+  lookStepLosesGlobe,
+} from './globeInView.js';
 import {
   projectEarthDiscToViewport,
   earthDiscScreenRadius,
   getKeyholeGeometry,
+  KEYHOLE_OUTER_RADIUS,
 } from './celestialRing.js';
+import { isScopeMaskEnabled } from './scopeMask.js';
 import {
   holdContinuousRender,
   releaseContinuousRender,
@@ -1046,6 +1054,187 @@ export function interruptCameraMotionIfActive(
   return interruptCameraMotion(reason);
 }
 
+// The frame share that in-place voice turns measure their limit against, with
+// the pose the last voice turn left the camera in. A turn that starts where
+// the last one left off keeps that baseline (raised if the planet now fills
+// more of the frame), so repeating a request cannot take a little more each
+// time. Once anything else has moved or turned the camera, a turn starts over
+// from what is on screen.
+let _lookBaseline = null;
+
+// The pre-check's proof that a half-degree turn from this pose keeps the planet
+// in view: which way, from which position and direction. A motion that starts from that
+// pose turns at least that far, so a request reported as done really moves
+// even when a smaller first step lands in a dip of the sampled share.
+const PROVEN_TURN_RAD = Cesium.Math.toRadians(0.5);
+let _provenLook = null;
+
+/** The part of the frame a viewer can see: the scope keyhole when it is on. */
+function visibleFrame() {
+  return { keyholeRadius: isScopeMaskEnabled() ? KEYHOLE_OUTER_RADIUS : 0 };
+}
+
+/** The frame share an in-place turn from `cam`'s pose is limited against. */
+function lookBaselineShare(cam) {
+  const share = globeFrameShare(cam, visibleFrame());
+  const continues =
+    _lookBaseline &&
+    Cesium.Cartesian3.equalsEpsilon(
+      _lookBaseline.position,
+      cam.positionWC,
+      0,
+      1,
+    ) &&
+    Cesium.Cartesian3.equalsEpsilon(
+      _lookBaseline.direction,
+      cam.directionWC,
+      0,
+      1e-9,
+    );
+  _lookBaseline = {
+    position: Cesium.Cartesian3.clone(cam.positionWC),
+    direction: Cesium.Cartesian3.clone(cam.directionWC),
+    share: continues ? Math.max(_lookBaseline.share, share) : share,
+  };
+  return _lookBaseline.share;
+}
+
+/**
+ * One in-place look step of motion `m`. From orbit a free globe camera turns
+ * only as far as keeps the planet in frame, measured against the baseline the
+ * turn started from, then the motion ends there.
+ */
+function lookWithinFrame(cam, m, look, angle) {
+  let allowed = angle;
+  if (isFreeGlobeCamera(_viewer)) {
+    if (m.globeShareAtStart === undefined) {
+      m.globeShareAtStart = lookBaselineShare(cam);
+      m.provenTurnRad = lookProven(cam, look) ? PROVEN_TURN_RAD : 0;
+      m.turnedRad = 0;
+    }
+    _provenLook = null;
+    allowed = lookAngleWithinFrame(cam, look, angle, {
+      ...visibleFrame(),
+      startShare: m.globeShareAtStart,
+    });
+    const owed = Math.min(angle, m.provenTurnRad - m.turnedRad);
+    if (allowed < owed) allowed = owed;
+    m.turnedRad += allowed;
+  }
+  if (allowed > 0) cam[look](allowed);
+  // The pose this turn leaves, for a turn that continues from it.
+  if (_lookBaseline)
+    Cesium.Cartesian3.clone(cam.directionWC, _lookBaseline.direction);
+  if (allowed < angle) interruptCameraMotion('globe-out-of-frame');
+}
+
+/**
+ * The in-place look a pitch change from `fromPitch` to `goalPitch` makes:
+ * 'lookUp', 'lookDown', or null when it does not move. A tilt is judged by
+ * the way its pitch moves, whatever form or direction word it came in.
+ */
+function tiltLook(fromPitch, goalPitch) {
+  if (!Number.isFinite(fromPitch) || !Number.isFinite(goalPitch)) return null;
+  if (goalPitch > fromPitch) return 'lookUp';
+  return goalPitch < fromPitch ? 'lookDown' : null;
+}
+
+/** Tilt `m` in place to `goalPitch`, as far as the frame limit allows. */
+function tiltInPlaceWithinFrame(cam, m, goalPitch) {
+  const look = tiltLook(cam.pitch, goalPitch);
+  if (look) lookWithinFrame(cam, m, look, Math.abs(goalPitch - cam.pitch));
+}
+
+/**
+ * The pitch an in-place tilt from `cam`'s pose toward `goalPitch` reaches
+ * before the frame limit stops it, judged as its steps will be: `goalPitch`
+ * itself when the planet stays in frame the whole way, or the camera is not a
+ * free globe camera. The steps run on a copy of the camera, each looking by
+ * the pitch still to go as the tilt's frames do, because a rolled camera's
+ * look turns its pitch by less than the look angle.
+ */
+function tiltPitchWithinFrame(cam, goalPitch) {
+  const look = tiltLook(cam.pitch, goalPitch);
+  if (!look || !isFreeGlobeCamera(_viewer)) return goalPitch;
+  const frame = { ...visibleFrame(), startShare: lookBaselineShare(cam) };
+  // A proven half degree is turned whatever the sampled share says.
+  let owed = lookProven(cam, look) ? PROVEN_TURN_RAD : 0;
+  const probe = Cesium.Camera.clone(cam);
+  for (let i = 0; i < 32; i += 1) {
+    if (tiltLook(probe.pitch, goalPitch) !== look) return goalPitch;
+    const angle = Math.abs(goalPitch - probe.pitch);
+    if (angle < 1e-6) return goalPitch;
+    const allowed = Math.max(
+      lookAngleWithinFrame(probe, look, angle, frame),
+      Math.min(angle, owed),
+    );
+    owed -= allowed;
+    if (allowed > 0) probe[look](allowed);
+    if (allowed < angle) return probe.pitch;
+  }
+  return probe.pitch;
+}
+
+/** The reply's note for a tilt the frame limit stops short of its angle. */
+function tiltFrameNote(pitch) {
+  return `Stopped at ${Math.round(Cesium.Math.toDegrees(pitch))}°: from this height a shallower angle would turn the globe out of view. Zoom in to tilt further.`;
+}
+
+/** True when the pre-check proved a half-degree `look` from `cam`'s pose. */
+function lookProven(cam, look) {
+  return (
+    _provenLook?.look === look &&
+    Cesium.Cartesian3.equalsEpsilon(
+      _provenLook.position,
+      cam.positionWC,
+      0,
+      1,
+    ) &&
+    Cesium.Cartesian3.equalsEpsilon(
+      _provenLook.direction,
+      cam.directionWC,
+      0,
+      1e-9,
+    )
+  );
+}
+
+/**
+ * The check a voice in-place turn (`look`: 'lookUp', 'lookDown', 'lookLeft'
+ * or 'lookRight') must pass from orbit: refused when even half a degree would
+ * cross the frame limit, otherwise proven for that half degree from this pose.
+ * With `released`, the turn runs through a navigation that first releases a
+ * tracked or locked camera and keeps its world pose. The frame measure and the
+ * turn are the same in any reference frame, so such a camera is judged as it
+ * is, before the release, and a refusal leaves tracking as it was. Otherwise a
+ * camera that is not a free globe camera is not checked. Returns the refusal,
+ * or null.
+ */
+function checkLookFromOrbit(look, { released = false } = {}) {
+  _provenLook = null;
+  if (_viewer.scene.mode !== Cesium.SceneMode.SCENE3D) return null;
+  const cam = _viewer.camera;
+  if (!released && !isFreeGlobeCamera(_viewer)) return null;
+  if (
+    lookStepLosesGlobe(cam, look, PROVEN_TURN_RAD, {
+      ...visibleFrame(),
+      startShare: lookBaselineShare(cam),
+    })
+  )
+    return {
+      ok: false,
+      action: 'move_camera',
+      error:
+        'From this height that would turn the globe out of view — zoom in first, or turn the other way.',
+    };
+  _provenLook = {
+    look,
+    position: Cesium.Cartesian3.clone(cam.positionWC),
+    direction: Cesium.Cartesian3.clone(cam.directionWC),
+  };
+  return null;
+}
+
 function clearLookAt() {
   try {
     _viewer.camera.lookAtTransform(Cesium.Matrix4.IDENTITY);
@@ -1226,12 +1415,7 @@ function onTick() {
         // Tracking can acquire the camera without going through navigation.
         // Yield without resetting its pose/frame: the world-space arc proof
         // only describes Cesium's rotation while the frame is identity.
-        if (
-          _viewer.scene.mode !== Cesium.SceneMode.SCENE3D ||
-          _viewer.trackedEntity ||
-          _isCockpitActive?.() ||
-          !Cesium.Matrix4.equals(cam.transform, Cesium.Matrix4.IDENTITY)
-        ) {
+        if (!isFreeGlobeCamera(_viewer) || _isCockpitActive?.()) {
           interruptCameraMotion('globe-camera-owner-changed');
           return;
         }
@@ -1253,8 +1437,14 @@ function onTick() {
           return;
         }
         cam.rotate(m.rotationAxis, angle);
-      } else if (m.direction === 'left') cam.lookLeft(stepRad);
-      else cam.lookRight(stepRad);
+      } else {
+        lookWithinFrame(
+          cam,
+          m,
+          m.direction === 'left' ? 'lookLeft' : 'lookRight',
+          stepRad,
+        );
+      }
     } else if (m.kind === 'route') {
       // The dolly's shaping lives in advanceRouteFlight(); the tick only
       // applies the pose and honours the same completion path as before.
@@ -1339,7 +1529,7 @@ function tickTilt(cam, m, scale, dt) {
       }
     }
   }
-  if (!m.hpr) cam.lookUp(limited - cam.pitch);
+  if (!m.hpr) tiltInPlaceWithinFrame(cam, m, limited);
   if (m.mode !== 'once' && (limited !== want || atLimit))
     interruptCameraMotion('tilt-clamp');
 }
@@ -1618,6 +1808,7 @@ export function initCameraVerbs(
   _isCockpitActive =
     typeof isCockpitActive === 'function' ? isCockpitActive : null;
   _viewer = viewer;
+  _lookBaseline = null;
   if (_tickRemover) _tickRemover();
   _tickRemover = viewer.clock.onTick.addEventListener(onTick);
   if (_trackingRemover) _trackingRemover();
@@ -1831,6 +2022,34 @@ export function moveCamera(args = {}, runNavigation = null) {
       };
     }
   }
+  // A tilt is judged by the way its pitch will move: toward its angle, or a
+  // nudge up or down; a rotate turns left only when told to, as it runs.
+  const look =
+    motion === 'tilt'
+      ? tiltLook(
+          _viewer.camera.pitch,
+          tiltToPitch ??
+            _viewer.camera.pitch +
+              Cesium.Math.toRadians(ONCE.tiltDeg) *
+                (direction === 'up' ? 1 : -1),
+        )
+      : motion === 'rotate'
+        ? direction === 'left'
+          ? 'lookLeft'
+          : 'lookRight'
+        : null;
+  // Honest limits from orbit too: a stopped turn rests within 0.05° of its
+  // limit, so one that cannot go half a degree further is refused rather than
+  // run and reported as done, and one that can is then turned at least that
+  // far. Near the limit the sampled share wobbles as the planet's edge crosses
+  // the grid, so a turn that would keep the planet can occasionally be refused
+  // too.
+  // A camera that is tracked or locked now is judged as the navigation that
+  // runs the turn will release it, so a refusal keeps the tracking.
+  const lookRefusal =
+    look &&
+    checkLookFromOrbit(look, { released: typeof runNavigation === 'function' });
+  if (lookRefusal) return lookRefusal;
   if (
     (motion === 'rotate_globe' ||
       (motion === 'orbit' && typeof runNavigation !== 'function')) &&
@@ -1914,9 +2133,17 @@ export function moveCamera(args = {}, runNavigation = null) {
         error: 'Globe rotation requires a clear ellipsoid bounding sphere.',
       };
   }
-  let horizonLimited = null;
+  // The angle a tilt to an angle stops at short of it, and why.
+  let stoppedAt = null;
+  let stopNote = null;
   const start = () => {
     interruptCameraMotion('replaced');
+    // Checked again only if the release left the camera somewhere other than
+    // where the check above expected it.
+    if (look && !lookProven(_viewer.camera, look)) {
+      const refusal = checkLookFromOrbit(look);
+      if (refusal) return refusal;
+    }
     const state = {
       kind: motion,
       direction: direction || 'right',
@@ -1935,10 +2162,20 @@ export function moveCamera(args = {}, runNavigation = null) {
       if (tiltToPitch !== null) {
         // From far out the place reaches its horizon before the camera
         // reaches the asked angle: stop there, and say so.
-        const goal =
+        let goal =
           tiltToPitch > from
             ? Math.min(tiltToPitch, Math.max(from, upLimit))
             : tiltToPitch;
+        if (goal !== tiltToPitch) stopNote = tiltHorizonNote(goal);
+        // From orbit an in-place tilt stops where the planet would leave the
+        // frame: aim it there, and say so.
+        if (!pivot) {
+          const framed = tiltPitchWithinFrame(_viewer.camera, goal);
+          if (framed !== goal) {
+            goal = framed;
+            stopNote = tiltFrameNote(goal);
+          }
+        }
         state.mode = 'once';
         state.direction = goal > from ? 'up' : 'down';
         state.goalPitch = goal;
@@ -1949,7 +2186,7 @@ export function moveCamera(args = {}, runNavigation = null) {
           ONCE.durationS,
           Math.abs(Cesium.Math.toDegrees(goal - from)) / TILT_TO_DEG_S,
         );
-        if (goal !== tiltToPitch) horizonLimited = goal;
+        if (goal !== tiltToPitch) stoppedAt = goal;
       } else {
         // A nudge stops at the limit it travels toward.
         const step =
@@ -2048,11 +2285,9 @@ export function moveCamera(args = {}, runNavigation = null) {
       speed,
       mode: state.mode,
       ...(tiltToPitch !== null && {
-        pitchDeg: Math.round(
-          Cesium.Math.toDegrees(horizonLimited ?? tiltToPitch),
-        ),
+        pitchDeg: Math.round(Cesium.Math.toDegrees(stoppedAt ?? tiltToPitch)),
       }),
-      ...(horizonLimited !== null && { note: tiltHorizonNote(horizonLimited) }),
+      ...(stopNote !== null && { note: stopNote }),
     };
   };
   const preserveCameraFlight =

src/globeInView.js

@@ -0,0 +1,179 @@
+import * as Cesium from 'cesium';
+
+// Cesium's free look (Shift+drag) turns the camera in place. Near the ground
+// that surveys a city; from orbit a few drags turn the whole planet out of
+// frame and leave only stars.
+export const FREE_LOOK_MAX_HEIGHT_METERS = 1_000_000;
+
+// A voice turn from orbit stops when about this share of the frame still shows
+// the planet's surface.
+export const MIN_GLOBE_FRAME_SHARE = 0.1;
+
+/**
+ * A free globe camera: the viewer is in 3D, follows no tracked entity, and its
+ * camera is not locked to a reference frame.
+ */
+export function isFreeGlobeCamera(viewer) {
+  return (
+    viewer.scene.mode === Cesium.SceneMode.SCENE3D &&
+    !viewer.trackedEntity &&
+    Cesium.Matrix4.equals(viewer.camera.transform, Cesium.Matrix4.IDENTITY)
+  );
+}
+
+const GRID_COLUMNS = 32;
+const GRID_ROWS = 18;
+// A turn across a sliver of planet moves its edge through sample points, so
+// the share wobbles by a cell or two without the planet leaving.
+const GRID_NOISE_CELLS = 2;
+// Whatever the baseline, a voice turn never takes the planet below this share
+// of the frame; a view that already shows less may only keep what it has.
+const LOOK_ABSOLUTE_FLOOR_SHARE = 0.01;
+const sampleRay = new Cesium.Ray();
+const sampleOffset = new Cesium.Cartesian3();
+
+/**
+ * Cast a 32×18 grid of view rays, one through the centre of each cell, at the
+ * WGS84 ellipsoid. With `keyholeRadius` (a radius around the frame centre, in
+ * units of half the frame height) only the cells inside that circle count: the
+ * scope mask hides the rest. Returns the surface hits and the cells counted, or
+ * null for a frustum other than a perspective one.
+ */
+function sampleFrame(camera, keyholeRadius) {
+  const frustum = camera.frustum;
+  if (!(frustum instanceof Cesium.PerspectiveFrustum)) return null;
+  const aspect = frustum.aspectRatio;
+  const tanY = Math.tan(frustum.fovy / 2);
+  const tanX = tanY * aspect;
+  const keyholeSquared = keyholeRadius > 0 ? keyholeRadius * keyholeRadius : 0;
+  Cesium.Cartesian3.clone(camera.positionWC, sampleRay.origin);
+  let hits = 0;
+  let cells = 0;
+  for (let row = 0; row < GRID_ROWS; row += 1) {
+    const rowY = (2 * (row + 0.5)) / GRID_ROWS - 1;
+    for (let column = 0; column < GRID_COLUMNS; column += 1) {
+      const columnX = (2 * (column + 0.5)) / GRID_COLUMNS - 1;
+      if (
+        keyholeSquared &&
+        (columnX * aspect) ** 2 + rowY * rowY > keyholeSquared
+      )
+        continue;
+      cells += 1;
+      Cesium.Cartesian3.multiplyByScalar(
+        camera.rightWC,
+        columnX * tanX,
+        sampleOffset,
+      );
+      Cesium.Cartesian3.add(
+        camera.directionWC,
+        sampleOffset,
+        sampleRay.direction,
+      );
+      Cesium.Cartesian3.multiplyByScalar(
+        camera.upWC,
+        rowY * tanY,
+        sampleOffset,
+      );
+      Cesium.Cartesian3.add(
+        sampleRay.direction,
+        sampleOffset,
+        sampleRay.direction,
+      );
+      Cesium.Cartesian3.normalize(sampleRay.direction, sampleRay.direction);
+      if (
+        Cesium.IntersectionTests.rayEllipsoid(sampleRay, Cesium.Ellipsoid.WGS84)
+      )
+        hits += 1;
+    }
+  }
+  return { hits, cells };
+}
+
+/**
+ * Share of the frame, from 0 to 1, that shows the planet's surface: the
+ * fraction of a 32×18 grid of view rays, one through the centre of each cell,
+ * that hit the WGS84 ellipsoid. With `keyholeRadius` (see `sampleFrame`) it is
+ * the share of the visible circle instead. A frustum other than a perspective
+ * one counts as fully covered.
+ */
+export function globeFrameShare(camera, { keyholeRadius = 0 } = {}) {
+  const sample = sampleFrame(camera, keyholeRadius);
+  if (!sample || sample.cells === 0) return 1;
+  return sample.hits / sample.cells;
+}
+
+/** True when none of the planet's surface is in `camera`'s visible frame. */
+export function globeOutOfFrame(camera, options) {
+  return globeFrameShare(camera, options) === 0;
+}
+
+const lookProbes = new WeakMap();
+const LOOK_EDGE_TOLERANCE = Cesium.Math.toRadians(0.05);
+
+/**
+ * How much of one in-place look step (`lookUp`, `lookDown`, `lookLeft` or
+ * `lookRight` by a non-negative `angle` in radians) keeps the planet in frame
+ * from orbit. Above the free-look height the step may not leave less than
+ * `MIN_GLOBE_FRAME_SHARE` of the visible frame on the planet, or less than
+ * `startShare` when that is lower, give or take two grid cells of sampling
+ * noise. However the baseline was taken, it never leaves less than 1% of the
+ * frame, and a view that already shows less may only keep or gain what it has.
+ * `startShare` is the baseline the turn is measured against (the current share
+ * by default): callers pass one value to every step of a motion, and to every
+ * turn that continues from where the last one left off, so the limit cannot
+ * slide down a step or a command at a time. `keyholeRadius` limits the measure
+ * to the scope's visible circle, as in `globeFrameShare`.
+ * With nothing on screen the limit is nothing either, so the step is left to
+ * the move-end recovery. Returns `angle` when the whole step fits, otherwise a
+ * smaller angle that fits, found by bisection to within 0.05°, so a stopped
+ * motion rests at the limit. Steps are tried on a copy; `camera` is not moved.
+ */
+export function lookAngleWithinFrame(
+  camera,
+  look,
+  angle,
+  { startShare, keyholeRadius = 0 } = {},
+) {
+  if (
+    !(angle > 0) ||
+    !(camera.positionCartographic?.height > FREE_LOOK_MAX_HEIGHT_METERS)
+  )
+    return angle;
+  const sample = sampleFrame(camera, keyholeRadius);
+  if (!sample || sample.cells === 0) return angle;
+  const share = sample.hits / sample.cells;
+  const baseline = startShare ?? share;
+  // Capped at what is on screen now, so a step that keeps or gains surface is
+  // never refused, even when the frame has shrunk since the baseline was taken
+  // (a resized window or a turned phone).
+  const floor = Math.min(
+    share,
+    Math.max(
+      Math.min(MIN_GLOBE_FRAME_SHARE, baseline) -
+        GRID_NOISE_CELLS / sample.cells,
+      Math.min(LOOK_ABSOLUTE_FLOOR_SHARE, baseline),
+    ),
+  );
+  const fits = (step) => {
+    const probe = Cesium.Camera.clone(camera, lookProbes.get(camera));
+    lookProbes.set(camera, probe);
+    probe[look](step);
+    // Shares are whole grid cells; the epsilon keeps rounding in `floor` from
+    // costing a cell.
+    return globeFrameShare(probe, { keyholeRadius }) >= floor - 1e-9;
+  };
+  if (fits(angle)) return angle;
+  let inside = 0;
+  let outside = angle;
+  while (outside - inside > LOOK_EDGE_TOLERANCE) {
+    const middle = (inside + outside) / 2;
+    if (fits(middle)) inside = middle;
+    else outside = middle;
+  }
+  return inside;
+}
+
+/** True when an in-place look step of `angle` would lose part of its turn. */
+export function lookStepLosesGlobe(camera, look, angle, options) {
+  return lookAngleWithinFrame(camera, look, angle, options) < angle;
+}