diff --git a/src/render/ContourBands.cpp b/src/render/ContourBands.cpp
index 817535e..894ed34 100644
--- a/src/render/ContourBands.cpp
+++ b/src/render/ContourBands.cpp
@@ -2,6 +2,7 @@
 
 #include <vtkBandedPolyDataContourFilter.h>
 #include <vtkCell.h>
+#include <vtkCellArray.h>
 #include <vtkCellData.h>
 #include <vtkDataSetSurfaceFilter.h>
 #include <vtkDoubleArray.h>
@@ -10,7 +11,7 @@
 #include <vtkPointData.h>
 #include <vtkPoints.h>
 #include <vtkPolyData.h>
-#include <vtkStructuredGrid.h>
+#include <vtkUnstructuredGrid.h>
 
 #include <cmath>
 
@@ -70,26 +71,49 @@ Grid smoothGrid(const Grid& g, double strength) {
     return out;
 }
 
-// 用 Grid 构 vtkStructuredGrid（点 (x[i], y[j], 0)；NaN 值置 0 但记录于掩膜——
-// 首版裁剪在 Task 1.4 接入，这里先全量）。
-vtkSmartPointer<vtkStructuredGrid> toStructuredGrid(const Grid& g) {
+// 把含任一 NaN 顶点的网格单元（quad）从网格中剔除→凸包裁剪。
+vtkSmartPointer<vtkUnstructuredGrid> toCellGrid(const Grid& g) {
     const int nx = g.nx(), ny = g.ny();
-    auto sg = vtkSmartPointer<vtkStructuredGrid>::New();
-    sg->SetDimensions(nx, ny, 1);
+    auto ug = vtkSmartPointer<vtkUnstructuredGrid>::New();
     vtkNew<vtkPoints> pts; pts->SetNumberOfPoints(static_cast<vtkIdType>(nx) * ny);
     vtkNew<vtkDoubleArray> sc; sc->SetName("v");
     sc->SetNumberOfTuples(static_cast<vtkIdType>(nx) * ny);
-    for (int j = 0; j < ny; ++j)
-        for (int i = 0; i < nx; ++i) {
-            const vtkIdType id = static_cast<vtkIdType>(j) * nx + i;
-            pts->SetPoint(id, g.x[i], g.y[j], 0.0);
-            const double v = g.valueAt(i, j);
-            sc->SetValue(id, std::isnan(v) ? 0.0 : v);
-        }
-    sg->SetPoints(pts);
-    sg->GetPointData()->SetScalars(sc);
-    return sg;
+    for (int j = 0; j < ny; ++j) for (int i = 0; i < nx; ++i) {
+        const vtkIdType id = static_cast<vtkIdType>(j) * nx + i;
+        pts->SetPoint(id, g.x[i], g.y[j], 0.0);
+        const double v = g.valueAt(i, j);
+        sc->SetValue(id, std::isnan(v) ? 0.0 : v);
+    }
+    ug->SetPoints(pts);
+    ug->GetPointData()->SetScalars(sc);
+    auto idAt = [nx](int i, int j) { return static_cast<vtkIdType>(j) * nx + i; };
+    for (int j = 0; j < ny - 1; ++j) for (int i = 0; i < nx - 1; ++i) {
+        if (!g.hasValue(i, j) || !g.hasValue(i+1, j) || !g.hasValue(i, j+1) || !g.hasValue(i+1, j+1))
+            continue;  // 含 NaN 的 quad 不入网格 → 凸包裁剪
+        vtkIdType quad[4] = { idAt(i,j), idAt(i+1,j), idAt(i+1,j+1), idAt(i,j+1) };
+        ug->InsertNextCell(VTK_QUAD, 4, quad);
+    }
+    return ug;
 }
+
+// Douglas-Peucker 等值线简化（就地）。
+void simplifyInPlace(std::vector<Vec2>& pts, double tol) {
+    if (tol <= 0 || pts.size() < 3) return;
+    std::vector<char> keep(pts.size(), 0); keep.front() = keep.back() = 1;
+    std::vector<std::pair<int,int>> st{{0, int(pts.size()) - 1}};
+    auto dist = [](const Vec2& p, const Vec2& a, const Vec2& b) {
+        double dx = b.x - a.x, dy = b.y - a.y, L = std::hypot(dx, dy);
+        if (L < 1e-12) return std::hypot(p.x - a.x, p.y - a.y);
+        return std::fabs((p.x - a.x) * dy - (p.y - a.y) * dx) / L; };
+    while (!st.empty()) { auto [s, e] = st.back(); st.pop_back();
+        double dmax = 0; int idx = -1;
+        for (int k = s + 1; k < e; ++k) { double d = dist(pts[k], pts[s], pts[e]);
+            if (d > dmax) { dmax = d; idx = k; } }
+        if (idx >= 0 && dmax > tol) { keep[idx] = 1; st.push_back({s, idx}); st.push_back({idx, e}); } }
+    std::vector<Vec2> r; for (size_t k = 0; k < pts.size(); ++k) if (keep[k]) r.push_back(pts[k]);
+    pts.swap(r);
+}
+
 }  // namespace
 
 ContourBandsResult buildContourBands(const Grid& g, const ColorScale& cs, const ContourOptions& opt) {
@@ -101,8 +125,7 @@ ContourBandsResult buildContourBands(const Grid& g, const ColorScale& cs, const
     if (stops.size() < 2) return out;
 
     Grid work = smoothGrid(upsampleBilinear(g, std::max(1, opt.upsample)), opt.smooth);
-    auto sg = toStructuredGrid(work);
-    vtkNew<vtkDataSetSurfaceFilter> surf; surf->SetInputData(sg);
+    vtkNew<vtkDataSetSurfaceFilter> surf; surf->SetInputData(toCellGrid(work));
     vtkNew<vtkBandedPolyDataContourFilter> banded;
     banded->SetInputConnection(surf->GetOutputPort());
     banded->SetNumberOfContours(static_cast<int>(stops.size()));
@@ -129,7 +152,7 @@ ContourBandsResult buildContourBands(const Grid& g, const ColorScale& cs, const
         out.bands.push_back(std::move(bp));
     }
 
-    // port1：等值线（polylines）。
+    // port1：等值线（polylines）+ DP 简化。
     vtkPolyData* edges = banded->GetContourEdgesOutput();
     if (edges) {
         edges->BuildCells();
@@ -142,6 +165,7 @@ ContourBandsResult buildContourBands(const Grid& g, const ColorScale& cs, const
                 double xyz[3]; cp->GetPoint(p, xyz);
                 cl.pts.push_back(Vec2{xyz[0], xyz[1]});
             }
+            simplifyInPlace(cl.pts, opt.simplifyTol);
             if (cl.pts.size() >= 2) out.lines.push_back(std::move(cl));
         }
     }
diff --git a/tests/render/test_contour_bands.cpp b/tests/render/test_contour_bands.cpp
index 7994241..c4b7b48 100644
--- a/tests/render/test_contour_bands.cpp
+++ b/tests/render/test_contour_bands.cpp
@@ -19,6 +19,23 @@ TEST(ContourBands, UpsampleIncreasesDetail) {
     EXPECT_GT(rb.bands.size(), ra.bands.size());
 }
 
+// 含 NaN 无效角的网格：裁剪后该角不应被任何色带覆盖（所有多边形顶点远离该角）。
+TEST(ContourBands, ClipsNaNRegion) {
+    Grid g(3, 3);
+    g.x = {0, 1, 2}; g.y = {0, 1, 2};
+    for (int j = 0; j < 3; ++j) for (int i = 0; i < 3; ++i) g.valueAt(i, j) = 5.0;
+    g.valueAt(2, 2) = std::nan("");  // 右上角无效
+    g.vmin = 0; g.vmax = 10;
+    ColorScale cs; cs.addStop(0, Rgba{0,0,255,255}); cs.addStop(10, Rgba{255,0,0,255});
+    ContourOptions opt; opt.upsample = 1; opt.smooth = 0; opt.simplifyTol = 0;
+    auto r = buildContourBands(g, cs, opt);
+    bool coversCorner = false;
+    for (const auto& b : r.bands)
+        for (const auto& p : b.ring)
+            if (p.x > 1.5 && p.y > 1.5) coversCorner = true;
+    EXPECT_FALSE(coversCorner);
+}
+
 // 2x2 平滑梯度网格 + 2 段色阶 → 至少 1 个色带多边形，多边形顶点 >=3。
 TEST(ContourBands, ProducesNonEmptyBands) {
     Grid g(3, 3);