fix(#9): hide globe when pivot is blockd by curvature

src/cameraSync.js

@@ -25,10 +25,10 @@ export function syncCameras(potreeViewer, cesiumViewer) {
     new Cesium.Cartesian3()
   ) 
 
-  // Hide globe when camera is below surface
-  const camHeight = Cesium.Cartographic.fromCartesian(cPos).height
-  cesiumViewer.scene.globe.show = camHeight >= 0;
-  cesiumViewer.scene.skyAtmosphere.show = camHeight >= 0;
+  // Hide globe when the camera is below the surface or blocked by the curvature of the Earth
+  const showGlobe = shouldShowGlobe(cPos, cTarget);
+  cesiumViewer.scene.globe.show = showGlobe;
+  cesiumViewer.scene.skyAtmosphere.show = showGlobe;
 
   cesiumViewer.camera.setView({
     destination: cPos,
@@ -46,4 +46,38 @@ export function syncCameras(potreeViewer, cesiumViewer) {
     const fovx = Math.atan(Math.tan(0.5 * fovy) * aspect) * 2
     cesiumViewer.camera.frustum.fov = fovx
   }
+}
+
+/**
+ * Determines whether the globe should be visible based on the camera position.
+ *
+ * Returns false if the camera is below the globe surface or if the pivot
+ * point would be blocked by the curvature of the Earth. This is handled 
+ * in a unified way by projecting the pivot to the globe surface and 
+ * comparing the camera and pivot positions along the axis from the Earth's 
+ * center through the pivot.
+ * 
+ * @param cameraPos - The camera position in Cesium Cartesian3 coordinates
+ * @param pivot - The pivot point in the point cloud (Cartesian3)
+ * @returns true if the globe should be visible, false if it should be hidden
+ */
+function shouldShowGlobe(cameraPos, pivot) {
+  const ellipsoid = Cesium.Ellipsoid.WGS84;
+  const earthCenter = Cesium.Cartesian3.ZERO;
+
+  // Get point on globe surface directly above the pivot
+  const carto = Cesium.Cartographic.fromCartesian(pivot);
+  const pivotSurface = Cesium.Cartesian3.fromRadians(carto.longitude, carto.latitude, 0, ellipsoid);
+
+  // Axis vector from Earth center through pivot
+  const axis = Cesium.Cartesian3.subtract(pivotSurface, earthCenter, new Cesium.Cartesian3());
+  Cesium.Cartesian3.normalize(axis, axis);
+
+  // Project camera and pivot onto this axis
+  const camProj = Cesium.Cartesian3.dot(cameraPos, axis);
+  const pivotProj = Cesium.Cartesian3.dot(pivotSurface, axis);
+
+  // If camera is "above" pivot on this axis, the globe should be visible
+  // If camera is "below" pivot on this axis, the globe should be not be visible
+  return camProj >= pivotProj;
 }