Removing applyConversion in VectorField API

src/parcels/_core/field.py

@@ -316,20 +316,18 @@ def eval(self, time: datetime, z, y, x, particles=None, applyConversion=True):
                 w = self.W._interp_method(self.W, ti, position, tau, time, z, y, x)
             else:
                 w = 0.0
-
-            if applyConversion:
-                u = self.U.units.to_target(u, z, y, x)
-                v = self.V.units.to_target(v, z, y, x)
-
         else:
-            (u, v, w) = self._vector_interp_method(self, ti, position, tau, time, z, y, x, applyConversion)
+            (u, v, w) = self._vector_interp_method(self, ti, position, tau, time, z, y, x)
+
+        if applyConversion:
+            u = self.U.units.to_target(u, z, y, x)
+            v = self.V.units.to_target(v, z, y, x)
+            if "3D" in self.vector_type:
+                w = self.W.units.to_target(w, z, y, x)
 
         for vel in (u, v, w):
             _update_particle_states_interp_value(particles, vel)
 
-        if applyConversion and ("3D" in self.vector_type):
-            w = self.W.units.to_target(w, z, y, x) if self.W else 0.0
-
         if "3D" in self.vector_type:
             return (u, v, w)
         else:

src/parcels/interpolators.py

@@ -52,7 +52,6 @@ def ZeroInterpolator_Vector(
     z: np.float32 | np.float64,
     y: np.float32 | np.float64,
     x: np.float32 | np.float64,
-    applyConversion: bool,
 ) -> np.float32 | np.float64:
     """Template function used for the signature check of the interpolation methods for velocity fields."""
     return 0.0
@@ -158,7 +157,6 @@ def CGrid_Velocity(
     z: np.float32 | np.float64,
     y: np.float32 | np.float64,
     x: np.float32 | np.float64,
-    applyConversion: bool,
 ):
     """
     Interpolation kernel for velocity fields on a C-Grid.
@@ -276,11 +274,7 @@ def CGrid_Velocity(
     U = (1 - xsi) * U0 + xsi * U1
     V = (1 - eta) * V0 + eta * V1
 
-    deg2m = 1852 * 60.0
-    if applyConversion:
-        meshJac = (deg2m * deg2m * np.cos(np.deg2rad(y))) if grid._mesh == "spherical" else 1
-    else:
-        meshJac = deg2m if grid._mesh == "spherical" else 1
+    meshJac = 1852 * 60.0 if grid._mesh == "spherical" else 1
 
     jac = i_u._compute_jacobian_determinant(py, px, eta, xsi) * meshJac
 
@@ -533,7 +527,6 @@ def XFreeslip(
     z: np.float32 | np.float64,
     y: np.float32 | np.float64,
     x: np.float32 | np.float64,
-    applyConversion: bool,
 ):
     """Free-slip boundary condition interpolation for velocity fields."""
     return _Spatialslip(vectorfield, ti, position, tau, t, z, y, x, a=1.0, b=0.0)
@@ -548,7 +541,6 @@ def XPartialslip(
     z: np.float32 | np.float64,
     y: np.float32 | np.float64,
     x: np.float32 | np.float64,
-    applyConversion: bool,
 ):
     """Partial-slip boundary condition interpolation for velocity fields."""
     return _Spatialslip(vectorfield, ti, position, tau, t, z, y, x, a=0.5, b=0.5)

tests/test_advection.py

@@ -457,7 +457,7 @@ def test_nemo_curvilinear_fieldset():
     U = parcels.Field("U", ds["U"], grid)
     V = parcels.Field("V", ds["V"], grid)
     U.units = parcels.GeographicPolar()
-    V.units = parcels.Geographic()
+    V.units = parcels.GeographicPolar()  # U and V need GoegraphicPolar for  C-Grid interpolation to work correctly
     UV = parcels.VectorField("UV", U, V, vector_interp_method=CGrid_Velocity)
     fieldset = parcels.FieldSet([U, V, UV])
 
@@ -543,7 +543,7 @@ def test_nemo_3D_curvilinear_fieldset(method):
     V = parcels.Field("V", ds["V"], grid)
     W = parcels.Field("W", ds["W"], grid)
     U.units = parcels.GeographicPolar()
-    V.units = parcels.Geographic()
+    V.units = parcels.GeographicPolar()  # U and V need GoegraphicPolar for C-Grid interpolation to work correctly
     UV = parcels.VectorField("UV", U, V, vector_interp_method=CGrid_Velocity)
     UVW = parcels.VectorField("UVW", U, V, W, vector_interp_method=CGrid_Velocity)
     fieldset = parcels.FieldSet([U, V, W, UV, UVW])

tests/test_field.py

@@ -159,7 +159,7 @@ def test_vectorfield_invalid_interpolator():
     ds = datasets_structured["ds_2d_left"]
     grid = XGrid.from_dataset(ds)
 
-    def invalid_interpolator_wrong_signature(self, ti, position, tau, t, z, y, applyConversion, invalid):
+    def invalid_interpolator_wrong_signature(self, ti, position, tau, t, z, y, invalid):
         return 0.0
 
     # Create component fields