丢弃 ESRI 灰色'Map data not yet available'错误瓦片，回退父级放大

src/scene/CesiumGlobe.js

@@ -241,10 +241,45 @@ export class CesiumGlobe {
     scene.maximumRenderTimeChange = Infinity; // 配合 requestRenderMode：静止时停止重绘，大幅省电省帧
 
     // 卫星影像
+    // 检测 ESRI "Map data not yet available" 灰色错误瓦片并丢弃，自动回退父级放大
+    const discardNotAvailableTile = {
+      _canvas: document.createElement('canvas'),
+      _ctx: null,
+      isReady() {
+        return true;
+      },
+      shouldDiscardImage(image) {
+        try {
+          if (!this._ctx) {
+            this._ctx = this._canvas.getContext('2d', { willReadFrequently: true });
+          }
+          this._canvas.width = 8;
+          this._canvas.height = 8;
+          this._ctx.drawImage(image, 0, 0, 8, 8);
+          const d = this._ctx.getImageData(0, 0, 8, 8).data;
+          let gray = 0;
+          let total = 0;
+          for (let i = 0; i < d.length; i += 4) {
+            const r = d[i];
+            const g = d[i + 1];
+            const b = d[i + 2];
+            const mx = Math.max(r, g, b);
+            const mn = Math.min(r, g, b);
+            if (mx - mn < 15 && r > 110 && r < 240) gray++;
+            total++;
+          }
+          return total > 0 && gray / total > 0.92;
+        } catch (e) {
+          return false;
+        }
+      },
+    };
+
     const imagery = new Cesium.UrlTemplateImageryProvider({
       url: IMAGERY_URL,
       credit: 'Imagery © Esri, Maxar, Earthstar Geographics',
       maximumLevel: 19,
+      tileDiscardPolicy: discardNotAvailableTile,
     });
     const imageryLayer = new Cesium.ImageryLayer(imagery, {
       // 卫星影像不覆盖极区（约 ±85° 外返回黑块），限制范围让极区用冰盖底色