fix(street-level): camera height over Google 3D, cast only when it helps, gate token

From the code review of #768:

- view.js measured the camera's height above ground with globe.getHeight,
  but Google 3D hides the globe, so coverage picked its zoom from the
  ellipsoidal height. Over a high city (Denver, ~1,600 m) a camera 500 m up
  read 2,100 m: coverage stayed at z12/z13, whose tiles are too big to cast,
  and lines stayed draped on the roofs. With the globe hidden, the bare-earth
  height from the ground caster now answers; coverage re-picks its zoom when
  the surface mode changes. Verified in Denver: terrain mode, z14, cast lines.
  The core's surface check uses the same helper (and no longer subtracts the
  2 m lift from the camera height).
- castTile rebuilt a tile even when no line could be cast (terrain proxy
  down, tile too big); it now leaves such tiles as they are.
- The feature gate read Street Level's share token as a literal `0`; it now
  takes it from LAYER_STATE_REGISTRY, since a rebase can reassign it.

New view.test.mjs covers the shown-globe, hidden-globe and no-sample cases.

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

src/layers/streetLevel/index.js

@@ -125,22 +125,23 @@ export function createStreetLevelLayer({
 
   /**
    * Camera height above the bare earth under it, for the surface mode. The
-   * ground comes from the caster's coarse grid; a cold cell is fetched once
-   * and the mode checked again when it lands.
+   * ground comes from the caster's coarse grid; a cold cell near enough to
+   * matter is fetched once and the mode checked again when it lands.
    */
   function cameraHeightForSurface() {
     const carto = state.viewer?.camera?.positionCartographic;
     if (!carto) return null;
-    const fallback = cameraHeightAboveGround(state.viewer);
-    if (!(fallback < SURFACE_WARM_BELOW_M)) return fallback;
+    const caster = parts.groundCaster;
+    const height = cameraHeightAboveGround(state.viewer, {
+      groundAt: caster.groundAt,
+    });
     const lon = (carto.longitude * 180) / Math.PI;
     const lat = (carto.latitude * 180) / Math.PI;
-    const ground = parts.groundCaster.heightAt(lon, lat);
-    if (ground !== null) return carto.height - ground;
-    parts.groundCaster.prepare([[lon, lat]]).then((ready) => {
-      if (ready) scheduleSurfaceSync();
-    });
-    return fallback;
+    if (caster.groundAt(lon, lat) === null && height < SURFACE_WARM_BELOW_M)
+      caster.prepare([[lon, lat]]).then((ready) => {
+        if (ready) scheduleSurfaceSync();
+      });
+    return height;
   }
 
   /**

src/layers/streetLevel/providers/mapillary/coverage.js

@@ -172,9 +172,12 @@ export function createCoverage({ state, source }) {
     const lines = entry.sequenceList
       .filter((sequence) => passesImageryFilter(sequence, filter()))
       .map((sequence) => sequence.coordinates);
-    state.context.groundCaster.prepareLines(lines, { signal }).then(() => {
+    const caster = state.context.groundCaster;
+    caster.prepareLines(lines, { signal }).then(() => {
       const attached = [...state.coverage.tiles.values()].includes(entry);
       if (signal.aborted || !attached || !terrainMode()) return;
+      // Nothing new to cast (terrain proxy down, tile too big): keep it draped.
+      if (!lines.some((coords) => caster.castLine(coords))) return;
       // Keep the draped lines until the cast ones are built, so nothing blinks.
       const previous = entry.primitives;
       entry.primitives = [];
@@ -393,7 +396,9 @@ export function createCoverage({ state, source }) {
   function refresh() {
     const viewer = state.viewer;
     if (!viewer || !state.context.isActive() || state.keyRequired) return;
-    const height = cameraHeightAboveGround(viewer);
+    const height = cameraHeightAboveGround(viewer, {
+      groundAt: state.context.groundCaster?.groundAt,
+    });
     const sequenceZoom = coverageZoomForHeight(height);
     const overviewZoom = sequenceZoom ? null : overviewZoomForHeight(height);
     const zoom = sequenceZoom ?? overviewZoom;
@@ -481,10 +486,15 @@ export function createCoverage({ state, source }) {
     notify();
   }
 
-  /** Redraw loaded tiles draped or cast after the core's surface mode changes. */
+  /**
+   * Redraw loaded tiles draped or cast after the core's surface mode changes,
+   * then re-pick the zoom: the bare-earth height under the camera that the
+   * change brings in can move it (a high city reads much closer to the street).
+   */
   function setSurface() {
     if (!state.context.isActive()) return;
     rebuild();
+    refresh();
   }
 
   /** Look a sequence up across loaded tiles. */

src/layers/streetLevel/view.js

@@ -1,13 +1,24 @@
 import * as Cesium from 'cesium';
 
 /**
- * Camera height above the surface under the camera, in metres. Falls back to
- * the ellipsoidal height when the globe has no height sample yet.
+ * Camera height above the surface under the camera, in metres. The globe's
+ * terrain answers when the globe is shown; Google 3D hides the globe, so
+ * there the bare-earth height from `groundAt(lon, lat)` answers instead
+ * (without it a camera over a city 1,600 m up reads 1,600 m too high). Falls
+ * back to the ellipsoidal height when neither has a sample yet.
+ * @param {object} viewer
+ * @param {{groundAt?: (lon: number, lat: number) => number|null}} [options]
  */
-export function cameraHeightAboveGround(viewer) {
+export function cameraHeightAboveGround(viewer, { groundAt } = {}) {
   const carto = viewer?.camera?.positionCartographic;
   if (!carto) return null;
-  const ground = viewer.scene?.globe?.getHeight?.(carto);
+  const globe = viewer.scene?.globe;
+  let ground = globe?.show === false ? null : globe?.getHeight?.(carto);
+  if (!Number.isFinite(ground))
+    ground = groundAt?.(
+      Cesium.Math.toDegrees(carto.longitude),
+      Cesium.Math.toDegrees(carto.latitude),
+    );
   return carto.height - (Number.isFinite(ground) ? ground : 0);
 }
 

src/layers/streetLevel/view.test.mjs

@@ -0,0 +1,44 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { cameraHeightAboveGround } from './view.js';
+
+const RAD = Math.PI / 180;
+/** A viewer 300 m above a street 1,600 m up (Denver-like). */
+function viewer({ globeShown, globeHeight }) {
+  return {
+    camera: {
+      positionCartographic: {
+        longitude: -104.99 * RAD,
+        latitude: 39.74 * RAD,
+        height: 1900,
+      },
+    },
+    scene: { globe: { show: globeShown, getHeight: () => globeHeight } },
+  };
+}
+
+test('a shown globe answers the ground under the camera', () => {
+  assert.equal(
+    cameraHeightAboveGround(viewer({ globeShown: true, globeHeight: 1600 })),
+    300,
+  );
+});
+
+test('a hidden globe (Google 3D) falls back to the bare-earth height', () => {
+  const calls = [];
+  const groundAt = (lon, lat) => {
+    calls.push([+lon.toFixed(2), +lat.toFixed(2)]);
+    return 1600;
+  };
+  // A hidden globe's getHeight is ignored even when it returns a number.
+  const hidden = viewer({ globeShown: false, globeHeight: 0 });
+  assert.equal(cameraHeightAboveGround(hidden, { groundAt }), 300);
+  assert.deepEqual(calls, [[-104.99, 39.74]]);
+});
+
+test('with no ground sample the ellipsoidal height is used', () => {
+  const hidden = viewer({ globeShown: false, globeHeight: 0 });
+  assert.equal(cameraHeightAboveGround(hidden), 1900);
+  assert.equal(cameraHeightAboveGround(hidden, { groundAt: () => null }), 1900);
+  assert.equal(cameraHeightAboveGround({}), null);
+});