polygonize: reject non-finite simplify_tolerance (nan, inf)

CHANGELOG.md

@@ -21,6 +21,12 @@
 
 #### Fixed
 
+- `polygonize` now rejects non-finite values for `simplify_tolerance`
+  (`nan`, `+inf`, `-inf`) with a clear `ValueError`. Previously `nan`
+  silently disabled simplification (because `nan > 0` is False) and
+  `+inf` collapsed every polygon to empty output. Matches the existing
+  `atol` / `rtol` validation contract: finite and non-negative. (#2575)
+
 - `reproject(..., bounds_policy="auto")` no longer crops valid edge data
   on ordinary geographic-to-projected reprojections. The old blow-up
   heuristic compared source span (e.g. degrees for EPSG:4326) against

xrspatial/polygonize.py

@@ -2280,10 +2280,15 @@ def polygonize(
             raise ValueError(
                 f"Incorrect transform length of {len(transform)} instead of 6")
 
-    # Check simplification parameters.
-    if simplify_tolerance is not None and simplify_tolerance < 0:
+    # Check simplification parameters.  Mirror the atol/rtol validation
+    # below: reject NaN and +/-inf along with negative values.  NaN would
+    # silently disable simplification because ``nan > 0`` is False, and
+    # +inf would collapse every polygon to empty output -- neither is
+    # what a caller asking for simplification wants.
+    if simplify_tolerance is not None and (
+            not np.isfinite(simplify_tolerance) or simplify_tolerance < 0):
         raise ValueError(
-            "simplify_tolerance must be non-negative, "
+            "simplify_tolerance must be a non-negative finite number, "
             f"got {simplify_tolerance}")
     if simplify_method not in ("douglas-peucker", "visvalingam-whyatt"):
         raise ValueError(

xrspatial/tests/test_polygonize.py

@@ -954,6 +954,34 @@ def test_negative_tolerance_raises(self):
         with pytest.raises(ValueError, match="simplify_tolerance"):
             polygonize(data, simplify_tolerance=-1.0)
 
+    @pytest.mark.parametrize("bad", [
+        float("nan"), float("inf"), float("-inf")])
+    def test_non_finite_tolerance_raises(self, bad):
+        """nan/inf/-inf for simplify_tolerance must raise ValueError.
+
+        Regression for #2575: ``nan`` silently disabled simplification
+        (because ``nan > 0`` is False) and ``inf`` collapsed every
+        polygon to empty output.  Mirror the atol/rtol validation
+        contract: require finite + non-negative.
+        """
+        raster = np.array([[1, 1], [1, 1]], dtype=np.int64)
+        data = xr.DataArray(raster)
+        with pytest.raises(ValueError, match="simplify_tolerance"):
+            polygonize(data, simplify_tolerance=bad)
+
+    def test_zero_and_small_positive_tolerance_still_work(self):
+        """0.0 and small positive tolerances must still be accepted.
+
+        Regression for #2575: guard against an over-eager fix that
+        bans non-positive values along with non-finite ones.
+        """
+        raster = np.array([[1, 1, 2, 2],
+                           [1, 1, 2, 2]], dtype=np.int64)
+        data = xr.DataArray(raster)
+        # Both calls should succeed without raising.
+        polygonize(data, simplify_tolerance=0.0)
+        polygonize(data, simplify_tolerance=1e-9)
+
     def test_invalid_method_raises(self):
         """Unknown method should raise ValueError."""
         raster = np.array([[1, 1], [1, 1]], dtype=np.int64)