cast to float64

cfgrib/dataset.py

@@ -314,11 +314,11 @@ class OnDiskArray:
     ] = attr.attrib(repr=False)
     missing_value: float
     geo_ndim: int = attr.attrib(default=1, repr=False)
-    dtype = np.dtype("float32")
+    dtype = np.dtype("float64")
 
     def build_array(self) -> np.ndarray:
         """Helper method used to test __getitem__"""
-        array = np.full(self.shape, fill_value=np.nan, dtype="float32")
+        array = np.full(self.shape, fill_value=np.nan, dtype="float64")
         for header_indexes, message_ids in self.field_id_index.items():
             # NOTE: fill a single field as found in the message
             message = self.index.get_field(message_ids[0])  # type: ignore
@@ -332,7 +332,7 @@ def __getitem__(self, item):
         header_item_list = expand_item(item[: -self.geo_ndim], self.shape)
         header_item = [{ix: i for i, ix in enumerate(it)} for it in header_item_list]
         array_field_shape = tuple(len(i) for i in header_item_list) + self.shape[-self.geo_ndim :]
-        array_field = np.full(array_field_shape, fill_value=np.nan, dtype="float32")
+        array_field = np.full(array_field_shape, fill_value=np.nan, dtype="float64")
         for header_indexes, message_ids in self.field_id_index.items():
             try:
                 array_field_indexes = [it[ix] for it, ix in zip(header_item, header_indexes)]