Fix NaN pixels producing spurious polygons in numpy/dask backends

xrspatial/polygonize.py

@@ -550,6 +550,15 @@ def _polygonize_numpy(
 ) -> Tuple[List[Union[int, float]], List[List[np.ndarray]]]:
 
     ny, nx = values.shape
+
+    # Mask NaN pixels for float arrays, matching the CuPy backend.
+    if np.issubdtype(values.dtype, np.floating):
+        nan_mask = ~np.isnan(values)
+        if mask is not None:
+            mask = mask & nan_mask
+        else:
+            mask = nan_mask
+
     if nx == 1:
         # Algorithm requires nx > 1 to differentiate between facing E
         # (forward == 1) and facing N (forward == nx), so add extra column to

xrspatial/tests/test_polygonize.py

@@ -540,6 +540,39 @@ def test_polygonize_1008_geopandas_batch_with_holes():
     assert_allclose(df.geometry.area.sum(), 36.0)
 
 
+@pytest.mark.parametrize("connectivity", [4, 8])
+def test_polygonize_nan_pixels_excluded(connectivity):
+    """NaN pixels in float rasters should not produce polygons (#1190)."""
+    data = np.array([
+        [1.0, np.nan],
+        [np.nan, 1.0],
+    ], dtype=np.float64)
+    raster = xr.DataArray(data)
+    values, polygons = polygonize(raster, connectivity=connectivity)
+    # No polygon should have a NaN value.
+    assert not any(np.isnan(v) for v in values), (
+        f"NaN-valued polygons emitted: {values}"
+    )
+    assert all(v == 1.0 for v in values)
+    # 4-connectivity: two separate 1-pixel regions; 8-connectivity: one region.
+    expected = 2 if connectivity == 4 else 1
+    assert len(polygons) == expected
+
+
+@pytest.mark.skipif(da is None, reason="dask not installed")
+def test_polygonize_nan_pixels_excluded_dask():
+    """Dask backend also masks NaN pixels (#1190)."""
+    data = np.array([
+        [1.0, np.nan, 2.0],
+        [np.nan, 1.0, np.nan],
+        [3.0, np.nan, 1.0],
+    ], dtype=np.float64)
+    raster = xr.DataArray(da.from_array(data, chunks=(2, 2)))
+    values, polygons = polygonize(raster, connectivity=4)
+    assert not any(np.isnan(v) for v in values)
+    assert set(values) == {1.0, 2.0, 3.0}
+
+
 class TestSimplifyHelpers:
     """Tests for internal simplification helper functions."""