Add regrid filter

src/anemoi/transform/fields.py

@@ -71,7 +71,6 @@ def __init__(self, field, **kwargs):
     def metadata(self, *args, **kwargs):
 
         if kwargs.get("namespace"):
-            assert kwargs.get("namespace") == "mars", kwargs
             assert len(args) == 0, (args, kwargs)
             mars = self._field.metadata(**kwargs).copy()
             for k in list(mars.keys()):

src/anemoi/transform/filters/regrid.py

@@ -0,0 +1,53 @@
+# (C) Copyright 2024 Anemoi contributors.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+
+
+import logging
+
+from ..fields import new_field_from_numpy
+from ..fields import new_fieldlist_from_list
+from ..filter import Filter
+from . import filter_registry
+
+LOG = logging.getLogger(__name__)
+
+
+@filter_registry.register("regrid")
+class RegridFilter(Filter):
+    """A filter to regrid fields using earthkit-regrid."""
+
+    def __init__(self, *, in_grid=None, out_grid=None, method="linear"):
+        self.in_grid = in_grid
+        self.out_grid = out_grid
+        self.method = method
+
+    def forward(self, data):
+        return self._interpolate(data, self.in_grid, self.out_grid, self.method)
+
+    def backward(self, data):
+        return self._interpolate(data, self.out_grid, self.in_grid, self.method)
+
+    def _interpolate(self, data, in_grid, out_grid, method):
+        from earthkit.regrid import interpolate
+
+        result = []
+        for field in data:
+            result.append(
+                new_field_from_numpy(
+                    interpolate(
+                        field.to_numpy(flatten=True),
+                        in_grid={"grid": in_grid},
+                        out_grid={"grid": out_grid},
+                        method=method,
+                    ),
+                    template=field,
+                )
+            )
+
+        return new_fieldlist_from_list(result)