Allow dataset to be rectified with decreasing x_coords

CHANGES.md

@@ -10,6 +10,8 @@
   `xcube_resampling.gridmapping.GridMapping`. These methods were only used by
   `xcube_resampling.rectify_dataset`; their updated implementations now live in
   `xcube_resampling.rectify._compute_source_tile_indexing`.
+- Added support for rectifying datasets with decreasing x-coordinate in 
+  `xcube_resampling.rectify_dataset`.
 
 
 ## Changes in 0.2.4

tests/test_rectify.py

@@ -89,6 +89,33 @@ def test_rectify_2x2_to_default(self):
             ),
         )
 
+    def test_rectify_2x2_decreasing_x_coords(self):
+        source_ds = create_2x2_dataset_with_irregular_coords()
+        source_ds = source_ds.isel({"x": slice(None, None, -1)})
+
+        target_gm = GridMapping.regular(
+            size=(4, 4), xy_min=(0, 50), xy_res=2, crs=CRS_WGS84
+        )
+        target_ds = rectify_dataset(
+            source_ds,
+            target_gm=target_gm,
+            interp_methods=0,
+            output_indices_names=("indices_lon", "indices_lat"),
+        )
+
+        np.testing.assert_almost_equal(
+            target_ds.rad.values,
+            np.array(
+                [
+                    [nan, nan, nan, nan],
+                    [nan, 1.0, 2.0, nan],
+                    [3.0, 3.0, 2.0, nan],
+                    [nan, 4.0, nan, nan],
+                ],
+                dtype=target_ds.rad.dtype,
+            ),
+        )
+
     def test_rectify_2x2_to_regular(self):
         source_ds = create_2x2_dataset_with_irregular_coords()
         target_ds = rectify_dataset(source_ds, interp_methods=0)

xcube_resampling/rectify.py

@@ -39,6 +39,8 @@
     SpatialInterpMethodStr,
 )
 from .gridmapping import GridMapping
+from .gridmapping.cfconv import get_dataset_grid_mapping_proxies
+from .gridmapping.helpers import from_lon_360
 from .utils import (
     SourceTileIndexing,
     _clip_if_needed,
@@ -128,6 +130,7 @@ def rectify_dataset(
         coordinate variables are ignored in the output.
     """
     source_ds = _select_variables(source_ds, variables)
+    source_ds = _ensure_increasing_x(source_ds)
 
     source_gm = source_gm or GridMapping.from_dataset(source_ds)
     source_ds = normalize_grid_mapping(source_ds, source_gm)
@@ -200,9 +203,11 @@ def _assemble_rectified_dataset(
     coords = source_ds.coords.to_dataset()
     coords = coords.drop_vars((src_x_name, src_y_name), errors="ignore")
 
-    target_coords = target_gm.to_coords()
-    coords[tgt_x_name] = target_coords[tgt_x_name]
-    coords[tgt_y_name] = target_coords[tgt_y_name]
+    tgt_x = target_gm.x_coords
+    if target_gm.is_lon_360:
+        tgt_x = from_lon_360(tgt_x)
+    coords[tgt_x_name] = tgt_x
+    coords[tgt_y_name] = target_gm.y_coords
     coords["spatial_ref"] = xr.DataArray(0, attrs=target_gm.crs.to_cf())
     target_ds = xr.Dataset(coords=coords, attrs=source_ds.attrs)
 
@@ -721,3 +726,13 @@ def _rectify_block(
     sampled = _sample_array_at_indices(data_array, ix[valid], iy[valid], interp_method)
     data_rectified[:, valid] = sampled
     return data_rectified
+
+
+def _ensure_increasing_x(ds: xr.Dataset) -> xr.Dataset:
+    gm_proxy = next(iter(get_dataset_grid_mapping_proxies(ds).values()))
+    x_coords = gm_proxy.coords.x
+    x_diff = x_coords[0, 1] - x_coords[0, 0]
+    if -180 < x_diff < 0:
+        x_dim = x_coords.dims[1]
+        ds = ds.isel({x_dim: slice(None, None, -1)})
+    return ds

xcube_resampling/reproject.py

@@ -37,6 +37,7 @@
     SpatialInterpMethodStr,
 )
 from .gridmapping import GridMapping
+from .gridmapping.helpers import from_lon_360
 from .utils import (
     SourceTileIndexing,
     _clip_if_needed,
@@ -187,12 +188,17 @@ def _assemble_reprojected_dataset(
     interp_methods: SpatialInterpMethods | None = None,
     fill_values: FillValues | None = None,
 ):
-    x_name, y_name = source_gm.xy_var_names
+    src_x_name, src_y_name = source_gm.xy_var_names
+    tgt_x_name, tgt_y_name = target_gm.xy_var_names
+
     coords = source_ds.coords.to_dataset()
-    coords = coords.drop_vars((x_name, y_name), errors="ignore")
-    x_name, y_name = target_gm.xy_var_names
-    coords[x_name] = target_gm.x_coords
-    coords[y_name] = target_gm.y_coords
+    coords = coords.drop_vars((src_x_name, src_y_name), errors="ignore")
+
+    tgt_x = target_gm.x_coords
+    if target_gm.is_lon_360:
+        tgt_x = from_lon_360(tgt_x)
+    coords[tgt_x_name] = tgt_x
+    coords[tgt_y_name] = target_gm.y_coords
     coords["spatial_ref"] = xr.DataArray(0, attrs=target_gm.crs.to_cf())
     target_ds = xr.Dataset(coords=coords, attrs=source_ds.attrs)