diff --git a/src/app/main.cpp b/src/app/main.cpp
index 26b6805..19f0271 100644
--- a/src/app/main.cpp
+++ b/src/app/main.cpp
@@ -167,6 +167,8 @@ void buildWorkbench(QMainWindow& window, geopro::data::LocalSampleRepository& re
     const double lat0 = median(baseGrid.lat);
     const double lon0 = median(baseGrid.lon);
     auto frame = std::make_shared<geopro::core::GeoLocalFrame>(lat0, lon0);
+    // 测线地表高程基准(地形 z rebase 用,使地形落在测线附近而非按绝对高程浮空)。
+    const double refElev = baseGrid.elevation.empty() ? 0.0 : median(baseGrid.elevation);
 
     // ── 中央 QVTK + Scene（竖直帘面场景）─────────────────────────────────
     // Scene 非 QObject：堆分配，用 widget 销毁信号清理（widget 随 window 销毁）。
@@ -348,7 +350,7 @@ void buildWorkbench(QMainWindow& window, geopro::data::LocalSampleRepository& re
     // frame/structure 全局共享；切视图/勾选变化都调用此函数重建当前视图。
     auto rebuildCentral = [scene, rendererPtr, renderWindowPtr, viewMode, &repo, frame, tree,
                            structure, showCurtain, showVoxel, showTerrain, showSlice, slicePlane,
-                           crs]() {
+                           crs, refElev]() {
         // 先拆除上次的切片 widget(独立于 scene actor，须显式关闭)，再按条件重建。
         if (*slicePlane) { (*slicePlane)->Off(); *slicePlane = nullptr; }
         scene->clear();
@@ -416,6 +418,9 @@ void buildWorkbench(QMainWindow& window, geopro::data::LocalSampleRepository& re
                     plane->SetSliceIndex(dims[0] / 2);
                     plane->SetLookupTable(lut);
                     plane->DisplayTextOn();
+                    // 左键拖动=移动切面(默认左键是取值光标十字,不直观)；中键仍可取值。
+                    plane->SetLeftButtonAction(vtkImagePlaneWidget::VTK_SLICE_MOTION_ACTION);
+                    plane->SetMiddleButtonAction(vtkImagePlaneWidget::VTK_CURSOR_ACTION);
                     plane->On();
                     *slicePlane = plane;
                 }
@@ -424,7 +429,9 @@ void buildWorkbench(QMainWindow& window, geopro::data::LocalSampleRepository& re
 
         // 三维「地形」图层：GDAL 读 DEM(高程)+影像(EPSG:3857)，重投影到世界系，warp 面 + 纹理。
         if (!is2D && *showTerrain && crs) {
-            auto terr = geopro::render::buildTerrain(repo.demPath(), repo.imagePath(), *frame, 1.0);
+            // zOffset=refElev 使地形落在测线地表高程附近(不按绝对高程浮空);zScale=1 真实起伏。
+            auto terr = geopro::render::buildTerrain(repo.demPath(), repo.imagePath(), *frame,
+                                                     refElev, 1.0);
             if (terr) scene->addActor(terr);
         }
 
diff --git a/src/render/actors/TerrainActor.cpp b/src/render/actors/TerrainActor.cpp
index 0b41e37..f793dad 100644
--- a/src/render/actors/TerrainActor.cpp
+++ b/src/render/actors/TerrainActor.cpp
@@ -92,7 +92,8 @@ Raster readGeo(GDALDataset* ds) {
 }  // namespace
 
 vtkSmartPointer<vtkActor> buildTerrain(const std::string& demPath, const std::string& imagePath,
-                                       const geopro::core::GeoLocalFrame& frame, double zScale)
+                                       const geopro::core::GeoLocalFrame& frame, double zOffset,
+                                       double zScale)
 {
     GDALAllRegister();
 
@@ -152,7 +153,7 @@ vtkSmartPointer<vtkActor> buildTerrain(const std::string& demPath, const std::st
             const vtkIdType id = static_cast<vtkIdType>(j) * dg.w + i;
             float z = elev[static_cast<size_t>(j) * dg.w + i];
             if (hasNoData && z == static_cast<float>(noData)) z = vmin;
-            points->SetPoint(id, local.x, local.y, z * zScale);
+            points->SetPoint(id, local.x, local.y, (z - zOffset) * zScale);  // rebase 到测线高程
             sc->SetValue(id, z);
             if (hasImage) {
                 const auto m = llTo3857.forward(ll.x, ll.y);  // (mercX, mercY)
diff --git a/src/render/actors/TerrainActor.hpp b/src/render/actors/TerrainActor.hpp
index 87f5497..4c29ff6 100644
--- a/src/render/actors/TerrainActor.hpp
+++ b/src/render/actors/TerrainActor.hpp
@@ -13,10 +13,13 @@ namespace geopro::render {
 // 高程作 z 起伏(vtkStructuredGrid 面)，影像按经纬→3857→像素 算纹理坐标贴面。
 // 影像加载失败则退化为按高程上色(无纹理)。读不到 DEM 返回空 actor。
 //
-// 依赖 GDAL/PROJ；调用方运行时须有 PROJ_DATA。zScale 为高程纵向夸张(地形通常 1.0~数倍)。
+// 依赖 GDAL/PROJ；调用方运行时须有 PROJ_DATA。
+// zOffset：从高程减去的基准(米)——传测线地表高程使地形落在测线附近(否则按绝对高程浮空,
+//          spec M-3 Z 基准)。世界 z = (elev - zOffset) * zScale。zScale 为纵向夸张。
 vtkSmartPointer<vtkActor> buildTerrain(const std::string& demPath,
                                        const std::string& imagePath,
                                        const geopro::core::GeoLocalFrame& frame,
+                                       double zOffset = 0.0,
                                        double zScale = 1.0);
 
 }  // namespace geopro::render
diff --git a/tests/render/test_terrain.cpp b/tests/render/test_terrain.cpp
index cb5f3f0..b8c937c 100644
--- a/tests/render/test_terrain.cpp
+++ b/tests/render/test_terrain.cpp
@@ -18,7 +18,7 @@ static const std::string kDir =
 // (需 PROJ_DATA + GDAL 运行时; tests CMake 注入 PROJ_DATA。)
 TEST(Terrain, BuildsTexturedSurfaceFromSampleDemImage) {
     GeoLocalFrame frame(22.546, 114.164);  // 测区附近(香港)
-    auto actor = geopro::render::buildTerrain(kDir + "dem.tif", kDir + "image.tif", frame, 1.0);
+    auto actor = geopro::render::buildTerrain(kDir + "dem.tif", kDir + "image.tif", frame);
     ASSERT_NE(actor.GetPointer(), nullptr);
     ASSERT_NE(actor->GetMapper(), nullptr);  // 成功读 DEM → 有 mapper(空 actor 无 mapper)
 }
diff --git a/tests/spike/render_verify.cpp b/tests/spike/render_verify.cpp
index d4cfa93..8fde7b2 100644
--- a/tests/spike/render_verify.cpp
+++ b/tests/spike/render_verify.cpp
@@ -152,7 +152,7 @@ int main() {
 
     // 7) DEM 地形 + 影像贴图 — GDAL 读 + 重投影到世界系 + warp 面 + 纹理
     {
-        auto terr = render::buildTerrain(dir + "dem.tif", dir + "image.tif", frame, 1.0);
+        auto terr = render::buildTerrain(dir + "dem.tif", dir + "image.tif", frame, 0.0, 1.0);
         vtkNew<vtkRenderer> ren; ren->SetBackground(0.50, 0.60, 0.72);
         if (terr) ren->AddActor(terr);
         render::applyFree3D(ren);