Masking: incorporate 'missing_value' meta data

src/finam/adapters/masking.py

@@ -28,10 +28,15 @@ class Masking(Adapter):
     Parameters
     ----------
     nodata : numeric, optional
-        Value to set at masked positions. Default: np.nan
+        Value to set at masked positions. Default: None
+        If None, will be determined from outputs "missing_value"
+        meta data or, if that is missing, from the inputs meta data.
+        In- and output "missing_value" can be different but if a
+        nodata value is given and output has a "missing_value", they
+        need to match (will not be overwritten).
     """
 
-    def __init__(self, nodata=np.nan):
+    def __init__(self, nodata=None):
         super().__init__()
         self.nodata = nodata
         self._canonical_mask = None
@@ -57,8 +62,11 @@ class Masking(Adapter):
 
     def _get_info(self, info):
         # info coming from output, set grid None to get the input grid
-        request = info.copy_with(grid=None)
+        request = info.copy_with(grid=None, missing_value=None)
         in_info = self.exchange_info(request)
+        # get missing value from cf-convention meta data (in/out can differ here)
+        out_nodata = info.meta.get("missing_value", None)
+        in_nodata = in_info.meta.get("missing_value", None)
 
         if info.grid is None:
             with ErrorLogger(self.logger):
@@ -81,11 +89,17 @@ class Masking(Adapter):
         # create_selection
         if self._sub_grid.mask is not None:
             self._canonical_mask = self._sub_grid.to_canonical(self._sub_grid.mask)
+            # check no-data value
+            if self.nodata is None:
+                self.nodata = out_nodata if out_nodata is not None else in_nodata
+            if self.nodata is None:
+                with ErrorLogger(self.logger):
+                    raise FinamMetaDataError("Couldn't determine no-data value.")
         else:
             self._canonical_mask = None
 
         # return output info
-        return in_info.copy_with(grid=info.grid)
+        return in_info.copy_with(grid=info.grid, missing_value=self.nodata)
 
     def _masks_compatible(self, sup_grid, sub_grid):
         if sup_grid.mask is None:

tests/adapters/test_masking.py

@@ -25,7 +25,8 @@ class TestMasking(unittest.TestCase):
         in_grid = EsriGrid(ncols=3, nrows=4, order="F")
         out_grid = EsriGrid(ncols=3, nrows=4, mask=mask, order="F")
 
-        in_info = Info(time=time, grid=in_grid, units="m")
+        # missing_value to indicate no-data value in masking adapter
+        in_info = Info(time=time, grid=in_grid, units="m", missing_value=-9999)
 
         in_data = np.zeros(shape=in_info.grid.data_shape, order=in_info.grid.order)
         in_data.data[0, 0] = 1.0
@@ -46,7 +47,8 @@ class TestMasking(unittest.TestCase):
         composition = Composition([source, sink], log_level="DEBUG")
         composition.initialize()
 
-        source.outputs["Output"] >> Masking(nodata=-9999) >> sink.inputs["Input"]
+        # no-data value from missing-value (from source)
+        source.outputs["Output"] >> Masking(nodata=None) >> sink.inputs["Input"]
 
         composition.connect()