diff --git a/src/app/TileBasemap.cpp b/src/app/TileBasemap.cpp
index 671b115..f095692 100644
--- a/src/app/TileBasemap.cpp
+++ b/src/app/TileBasemap.cpp
@@ -114,6 +114,7 @@ void TileBasemap::show(Kind kind) {
     inFlight_.clear();
     terrainInFlight_.clear();
     desired_.clear();
+    terrainProbed_ = false;
     kind_ = kind;
     if (kind == Hidden) {
         if (rw_) rw_->Render();
@@ -280,18 +281,26 @@ void TileBasemap::placeTile(long long key, int z, int x, int y, const QImage& im
 }
 
 void TileBasemap::fetchTerrain(int z, int x, int y, long long key) {
-    if (z > kDemMaxZoom) return;             // 高层级无 DEM → 维持平面
     if (terrainInFlight_.count(key)) return;
+    // Terrarium 数据约到 z15；更高层级取覆盖本块的祖先 DEM 瓦片，按经纬采样其子区域。
+    const int dz = std::min(z, kDemMaxZoom);
+    const int shift = z - dz;
+    const int dx = x >> shift, dy = y >> shift;
+    if (!terrainProbed_) {
+        terrainProbed_ = true;
+        qInfo() << "[basemap] 首次拉DEM 卫星z=" << z << " → DEMz=" << dz << "(" << dx << "," << dy
+                << ")";
+    }
     // 必须 https：该 S3 桶对纯 http 返回 403（实测）。
     const QString url =
         QStringLiteral("https://s3.amazonaws.com/elevation-tiles-prod/terrarium/%1/%2/%3.png")
-            .arg(z)
-            .arg(x)
-            .arg(y);
+            .arg(dz)
+            .arg(dx)
+            .arg(dy);
     const int gen = generation_;
     terrainInFlight_.insert(key);
     QNetworkReply* reply = nam_.get(QNetworkRequest(QUrl(url)));
-    connect(reply, &QNetworkReply::finished, this, [this, reply, key, z, x, y, gen]() {
+    connect(reply, &QNetworkReply::finished, this, [this, reply, key, z, x, y, dz, dx, dy, gen]() {
         reply->deleteLater();
         terrainInFlight_.erase(key);
         if (gen != generation_ || kind_ != Satellite) return;
@@ -305,11 +314,12 @@ void TileBasemap::fetchTerrain(int z, int x, int y, long long key) {
             qWarning() << "[basemap] DEM 解码失败" << reply->url().toString();
             return;
         }
-        applyTerrain(key, z, x, y, dem);
+        applyTerrain(key, z, x, y, dz, dx, dy, dem);
     });
 }
 
-void TileBasemap::applyTerrain(long long key, int z, int x, int y, const QImage& dem) {
+void TileBasemap::applyTerrain(long long key, int sz, int sx, int sy, int dz, int dx, int dy,
+                               const QImage& dem) {
     auto it = placed_.find(key);
     if (it == placed_.end()) return;
     vtkSmartPointer<vtkTexture> tex = it->second->GetTexture();  // 复用已贴卫星纹理
@@ -317,24 +327,35 @@ void TileBasemap::applyTerrain(long long key, int z, int x, int y, const QImage&
     if (!haveBaseline_) {  // 基准高程取首块中心 → 地形整体绕 z=0 起伏
         baseline_ = demElev(dem, 0.5, 0.5);
         haveBaseline_ = true;
+        double mn = 1e30, mx = -1e30;
+        for (int yy = 0; yy < dem.height(); yy += 16)
+            for (int xx = 0; xx < dem.width(); xx += 16) {
+                const double e = demElev(dem, xx / double(dem.width() - 1),
+                                         yy / double(dem.height() - 1));
+                mn = std::min(mn, e);
+                mx = std::max(mx, e);
+            }
+        qInfo() << "[basemap] 地形启用 baseline=" << baseline_ << "m 首块高程范围[" << mn << ","
+                << mx << "]m 起伏=" << (mx - mn) << "m";
     }
-    auto warped = buildWarped(z, x, y, tex, dem);
+    auto warped = buildWarped(sz, sx, sy, dz, dx, dy, tex, dem);
     scene_.renderer()->RemoveViewProp(it->second);
     scene_.addActor(warped);
     it->second = warped;
     if (rw_) rw_->Render();
 }
 
-vtkSmartPointer<vtkActor> TileBasemap::buildWarped(int z, int x, int y,
+vtkSmartPointer<vtkActor> TileBasemap::buildWarped(int sz, int sx, int sy, int dz, int dx, int dy,
                                                    vtkSmartPointer<vtkTexture> tex,
                                                    const QImage& dem) {
-    const geopro::render::LonLatBox b = geopro::render::tileBounds(z, x, y);
-    const auto sw = frame_->toLocal(b.south, b.west);
-    const auto se = frame_->toLocal(b.south, b.east);
-    const auto nw = frame_->toLocal(b.north, b.west);
-    const double base = kGroundZ + (z - kMinZoom) * kZEps;
+    const geopro::render::LonLatBox sb = geopro::render::tileBounds(sz, sx, sy);  // 卫星块(几何)
+    const geopro::render::LonLatBox db = geopro::render::tileBounds(dz, dx, dy);  // DEM 块(采样)
+    const auto sw = frame_->toLocal(sb.south, sb.west);
+    const auto se = frame_->toLocal(sb.south, sb.east);
+    const auto nw = frame_->toLocal(sb.north, sb.west);
+    const double base = kGroundZ + (sz - kMinZoom) * kZEps;
 
-    // PlaneSource(等距圆柱下平面插值即正确 x/y) + 自动 tcoord；再按高程位移每点 Z。
+    // PlaneSource(等距圆柱下平面插值即正确 x/y) + 自动 tcoord；再按各点真实经纬采 DEM 位移 Z。
     vtkNew<vtkPlaneSource> plane;
     plane->SetOrigin(sw.x, sw.y, base);
     plane->SetPoint1(se.x, se.y, base);
@@ -346,11 +367,16 @@ vtkSmartPointer<vtkActor> TileBasemap::buildWarped(int z, int x, int y,
     warped->DeepCopy(plane->GetOutput());
     vtkDataArray* tc = warped->GetPointData()->GetTCoords();
     vtkPoints* pts = warped->GetPoints();
+    const double sLonSpan = sb.east - sb.west, sLatSpan = sb.north - sb.south;
+    const double dLonSpan = db.east - db.west, dLatSpan = db.north - db.south;
     const vtkIdType n = pts->GetNumberOfPoints();
     for (vtkIdType id = 0; id < n; ++id) {
         double t[2];
-        tc->GetTuple(id, t);
-        const double fx = t[0], fy = 1.0 - t[1];  // tcoord v: 南0北1 → fy: 北0南1(对齐 DEM 顶行=北)
+        tc->GetTuple(id, t);  // u:西0东1, v:南0北1
+        const double lon = sb.west + t[0] * sLonSpan;
+        const double lat = sb.south + t[1] * sLatSpan;
+        const double fx = (lon - db.west) / dLonSpan;        // DEM 块内列比例
+        const double fy = (db.north - lat) / dLatSpan;       // DEM 顶行=北 → fy
         const double elev = demElev(dem, fx, fy);
         double p[3];
         pts->GetPoint(id, p);
diff --git a/src/app/TileBasemap.hpp b/src/app/TileBasemap.hpp
index d5873e1..3020d4e 100644
--- a/src/app/TileBasemap.hpp
+++ b/src/app/TileBasemap.hpp
@@ -42,9 +42,11 @@ private:
     bool computeView(double& centerLat, double& centerLon, int& zoom) const;
     void fetchTile(int z, int x, int y, long long key);
     void placeTile(long long key, int z, int x, int y, const QImage& img);
-    void fetchTerrain(int z, int x, int y, long long key);          // 拉对应 DEM 瓦片(卫星模式)
-    void applyTerrain(long long key, int z, int x, int y, const QImage& dem);  // 平面块换起伏块
-    vtkSmartPointer<vtkActor> buildWarped(int z, int x, int y, vtkSmartPointer<vtkTexture> tex,
+    void fetchTerrain(int z, int x, int y, long long key);  // 拉覆盖该瓦片的 DEM(z>15 取祖先块)
+    void applyTerrain(long long key, int sz, int sx, int sy, int dz, int dx, int dy,
+                      const QImage& dem);  // 平面块换起伏块
+    vtkSmartPointer<vtkActor> buildWarped(int sz, int sx, int sy, int dz, int dx, int dy,
+                                          vtkSmartPointer<vtkTexture> tex,
                                           const QImage& dem);  // DEM 位移网格 + 卫星贴图
     static void onInteractionEnd(vtkObject*, unsigned long, void* clientData, void*);
 
@@ -60,6 +62,7 @@ private:
     std::set<long long> terrainInFlight_;                   // DEM 瓦片在途请求
     double baseline_ = 0.0;                                 // 基准高程(首块中心)，地形绕 z=0 起伏
     bool haveBaseline_ = false;
+    bool terrainProbed_ = false;                           // 首次 fetchTerrain 打一行诊断日志
     vtkSmartPointer<vtkInteractorObserver> styleObs_;       // 持引用保证回调期有效
     vtkSmartPointer<vtkCallbackCommand> observer_;
     bool refreshing_ = false;