Handle chunks of all null values

raster_tools/raster.py

@@ -1024,7 +1024,9 @@ def to_vector(self):
             dd.from_delayed(_vectorize(*chunk), meta=meta) for chunk in chunks
         ]
         ddf = dd.concat(results)
-        return ddf
+        # Add astype() as a workaround for
+        # https://github.com/geopandas/dask-geopandas/issues/190
+        return ddf.astype({"band": int, "row": int, "col": int})
 
 
 _XY_OFFSET_REMAP = {"ul": "ll", "ll": "ul", "ur": "lr", "lr": "ur"}
@@ -1083,10 +1085,17 @@ def _extract_values(data, mask):
 @dask.delayed
 def _vectorize(data, mask, cx, cy, band, crs, affine):
     xpoints, ypoints = _extract_points(mask, cx, cy)
-    values = _extract_values(data, mask)
-    points = [Point(x, y) for x, y in zip(xpoints, ypoints)]
-    rows, cols = xy_to_rowcol(xpoints, ypoints, affine)
-    bands = [band] * len(values)
+    if len(xpoints):
+        values = _extract_values(data, mask)
+        points = [Point(x, y) for x, y in zip(xpoints, ypoints)]
+        rows, cols = xy_to_rowcol(xpoints, ypoints, affine)
+        bands = [band] * len(values)
+    else:
+        values = []
+        points = []
+        bands = []
+        rows = []
+        cols = []
     df = gpd.GeoDataFrame(
         {
             "value": values,

tests/test_raster.py

@@ -861,8 +861,6 @@ def test_burn_mask():
     assert rs.null_value == 999
     true_state = data > 15
     true_state = np.where(data >= 20, False, true_state)
-    print(rs.burn_mask()._values)
-    print(true_state)
     assert np.allclose(rs.burn_mask(), true_state)
 
 
@@ -965,6 +963,27 @@ def test_to_vector():
     assert np.all(ddf.columns == ["value", "band", "row", "col", "geometry"])
     _compare_raster_to_vectorized(rs, df)
 
+    # make sure that empty (all-null) chunks are handled
+    data = np.array(
+        [
+            [
+                [0, 0, 1, 2],
+                [0, 0, 2, 2],
+                [0, 0, 1, 0],
+                [0, 1, 3, 0],
+            ]
+        ]
+    )
+    count = np.sum(data > 0)
+    rs = Raster(data).set_null_value(0)
+    rs.xrs.data = dask.array.rechunk(rs.xrs.data, (1, 2, 2))
+    rs._mask = dask.array.rechunk(rs._mask, (1, 2, 2))
+    ddf = rs.to_vector()
+    df = ddf.compute()
+
+    assert len(df) == count
+    _compare_raster_to_vectorized(rs, df)
+
 
 if __name__ == "__main__":
     unittest.main()