Normalize wind direction angles

Correctly find the differences between measured angles

camille/core.cpp

@@ -218,8 +218,15 @@ double veer(double dir_upr,
             double dir_lwr,
             double hgt_upr,
             double hgt_lwr) noexcept {
+    using std::atan2;
+    using std::sin;
+    using std::cos;
+    double a = dir_upr - dir_lwr;
+
+    // Normalize angular difference
+    double n = atan2(sin(a), cos(a));
 
-    return (dir_upr - dir_lwr) / (hgt_upr - hgt_lwr);
+    return n / (hgt_upr - hgt_lwr);
 }
 
 static const auto planar_windspeed_docstring = R"(

camille/lidar.py

@@ -64,8 +64,10 @@ def extrapolate_winddirection(df, height):
     pandas.Series
         Wind direction at target height
     """
-    hwd = df.dir + df.veer * (height - df.height)
-    return hwd
+
+    hwd = df.dir.values + df.veer.values * (height - df.height.values)
+    hwd = np.arcsin(np.sin(hwd))  # Normalize direction
+    return pd.Series(hwd, index=df.index)
 
 
 def windfield_desc(df, dist, hub_height, lidar_height_offset):

tests/process/test_lidar.py

@@ -209,9 +209,9 @@ def test(args):
         p = np.array([dist, 0, lidar_hgt])
         for _, row in processed.iterrows():
             assert row.hws == ref_speed(windfield, p)
-            assert row.hwd == ref_direction(windfield)
             assert row.shear == ref_shear(windfield)
             assert row.veer == ref_veer(windfield)
+            assert row.hwd == ref_direction(windfield)
     return test