标记便签：加缩放距离限制并修复背面可见问题

src/scene/CesiumGlobe.js

@@ -271,17 +271,21 @@ export class CesiumGlobe {
   _updateMarkerLayer() {
     const scene = this.viewer.scene;
     const camera = scene.camera;
-    const toPos = new Cesium.Cartesian3();
+    const outOfRange = camera.positionCartographic.height > 1e7; // 最远 1 万 km 内显示
+
     for (const m of this.markers) {
       const el = m.el;
       if (!el) continue;
+      if (outOfRange) { el.style.display = 'none'; continue; }
+
       const win = Cesium.SceneTransforms.worldToWindowCoordinates(scene, m.position);
       if (!win) { el.style.display = 'none'; continue; }
-      Cesium.Cartesian3.subtract(m.position, camera.positionWC, toPos);
-      if (Cesium.Cartesian3.dot(toPos, camera.directionWC) < 0) {
-        el.style.display = 'none'; // 背对相机不显示
-        continue;
-      }
+
+      // 背面（远半球）隐藏：dot(P, C) <= |P|² 时为背对地球
+      const dotPC = Cesium.Cartesian3.dot(m.position, camera.positionWC);
+      const r2 = Cesium.Cartesian3.magnitudeSquared(m.position);
+      if (dotPC <= r2) { el.style.display = 'none'; continue; }
+
       el.style.display = 'block';
       el.style.left = `${win.x}px`;
       el.style.top = `${win.y}px`;