do not apply scale/offset in datamet reader, leave it to xarray inste…

…ad (#209)
openradar · Sep 19, 2024 · 71ebcc6 · 71ebcc6
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diff --git a/docs/history.md b/docs/history.md
@@ -1,5 +1,9 @@
 # History
 
+## development version
+
+FIX: do not apply scale/offset in datamet reader, leave it to xarray instead ({pull}`209`) by [@kmuehlbauer](https://github.com/kmuehlbauer).
+
 ## 0.6.4 (2024-08-30)
 
 FIX: Notebooks are now conforming to ruff's style checks by [@rcjackson](https://github.com/rcjackson), ({pull}`199`) by [@rcjackson](https://github.com/rcjackson).

diff --git a/tests/io/test_datamet.py b/tests/io/test_datamet.py
@@ -44,14 +44,14 @@ def test_moment_metadata(data):
 @pytest.mark.parametrize(
     "moment, expected_value",
     [
-        ("UZ", -3.5),
-        ("CZ", -3.5),
-        ("V", 2.3344999999999985),
-        ("W", 16.0),
-        ("ZDR", 0.6859999999999999),
-        ("PHIDP", 94.06648),
-        ("RHOHV", 1.9243000000000001),
-        ("KDP", 0.5190000000000001),
+        ("UZ", 56),
+        ("CZ", 56),
+        ("V", 139),
+        ("W", 30),
+        ("ZDR", 137),
+        ("PHIDP", 16952),
+        ("RHOHV", 237),
+        ("KDP", 67),
     ],
 )
 def test_moment_data(data, moment, expected_value):

diff --git a/xradar/io/backends/datamet.py b/xradar/io/backends/datamet.py
@@ -163,24 +163,13 @@ def get_moment(self, mom, sweep):
         mom_path = os.path.join(".", mom, str(sweep + 1))
         mom_medata = self.get_mom_metadata(mom, sweep)
 
-        offset = float(mom_medata.get("offset") or 1.0)
-        slope = float(mom_medata.get("slope") or 1.0)
-        maxval = mom_medata.get("maxval")
-
-        if maxval:
-            maxval = float(maxval)
-            top = 255
-            bottom = float(mom_medata["bottom"])
-            slope = (maxval - offset) / (top - bottom)
-
         bitplanes = 16 if mom == "PHIDP" else int(mom_medata["bitplanes"] or 8)
         nazim = int(mom_medata.get("nlines"))
         nrange = int(mom_medata.get("ncols"))
 
         dtype = np.uint16 if bitplanes == 16 else np.uint8
         data = self.extract_data(mom_path, dtype)
-        data = slope * np.reshape(data, (nazim, nrange)) + offset
-        data[data < offset + 1e-5] = np.nan
+        data = np.reshape(data, (nazim, nrange))
 
         return data
 
@@ -272,8 +261,15 @@ def open_store_variable(self, mom):
         encoding = {"group": self._group, "source": self._filename}
 
         mom_metadata = self.root.get_mom_metadata(mom, self._group)
-        add_offset = mom_metadata.get("offset")
-        scale_factor = mom_metadata.get("slope")
+        add_offset = float(mom_metadata.get("offset") or 0.0)
+        scale_factor = float(mom_metadata.get("slope") or 1.0)
+        maxval = mom_metadata.get("maxval", None)
+
+        if maxval is not None:
+            maxval = float(maxval)
+            top = 255
+            bottom = float(mom_metadata["bottom"])
+            scale_factor = (maxval + add_offset) / (top - bottom)
 
         mname = datamet_mapping.get(mom, mom)
         mapping = sweep_vars_mapping.get(mname, {})