diff --git a/B04_PreProcess/B04_PreProcess_Engine_Contour.py b/B04_PreProcess/B04_PreProcess_Engine_Contour.py
index 7ede4004d..30a6946a1 100644
--- a/B04_PreProcess/B04_PreProcess_Engine_Contour.py
+++ b/B04_PreProcess/B04_PreProcess_Engine_Contour.py
@@ -428,6 +428,20 @@ def extract_contours(
         )
 
     if representation == "local_rbf_height_field":
+        # 굳힌 격자(641-1)가 있으면 그 면 그대로 — 등고선 = 서버 표본 · 종횡단과 같은 면(643)
+        filter_key = model_npz_path.stem.removeprefix("implicit_")
+        if (model_npz_path.parent / f"dtm_{filter_key}.npz").is_file():
+            from common_util.common_util_surface_sampler import implicit_grid_npz
+
+            with np.load(implicit_grid_npz(model_npz_path.parent, filter_key)) as grid:
+                return extract_contours_from_grid(
+                    grid["x"],
+                    grid["y"],
+                    grid["z"],
+                    grid["valid_mask"],
+                    interval,
+                    scene_center=scene_center,
+                )
         centers_xy, center_z = data["centers_xy"], data["center_z"]
         smoothing = float(data["smoothing"][0])
         interpolator = RBFInterpolator(
diff --git a/resources/tester/test_641_1_implicit_grid.py b/resources/tester/test_641_1_implicit_grid.py
index 1609f5a59..66d93c38f 100644
--- a/resources/tester/test_641_1_implicit_grid.py
+++ b/resources/tester/test_641_1_implicit_grid.py
@@ -161,3 +161,17 @@ def test_B07_음영_implicit_확정이면_평활_DTM(tmp_path, monkeypatch):
     ):
         basin._hillshade_for_box(SimpleNamespace(surface_params=params, project_root=tmp_path), box)
         assert opened[-1] == name
+
+
+def test_643_등고선_굳힌_격자_그대로(tmp_path):
+    from B04_PreProcess.B04_PreProcess_Engine_Contour import extract_contours
+
+    models = _project(tmp_path)
+    contours = extract_contours(
+        models / "implicit_classification.npz", "local_rbf_height_field", 1.0
+    )
+    points = np.array([p for c in contours for p in c["coordinates"]])
+    sampler = build_surface_sampler(models, "classification", "implicit", False)
+    z, valid = sampler.sample_xy(points[:, :2])
+    assert valid.sum() > 0.9 * len(points)
+    assert np.abs(z[valid] - points[valid, 2]).max() < 0.005  # 등고선 = 표본 면(좌표 mm 자리)