Removing UnitConverters from v4 (attempt 2)

docs/user_guide/examples/explanation_kernelloop.md

@@ -43,6 +43,7 @@ Besides having commutable Kernels, the main advantage of this implementation is
 Below is a simple example of some particles at the surface of the ocean. We create an idealised zonal wind flow that will "push" a particle that is already affected by the surface currents. The Kernel loop ensures that these two forces act at the same time and location.
 
 ```{code-cell}
+:tags: [hide-output]
 import matplotlib.pyplot as plt
 import numpy as np
 import xarray as xr
@@ -69,21 +70,18 @@ ds_fields["VWind"] = xr.DataArray(
 
 fieldset = parcels.FieldSet.from_copernicusmarine(ds_fields)
 
-# Set unit converters for custom wind fields
-fieldset.UWind.units = parcels.GeographicPolar()
-fieldset.VWind.units = parcels.Geographic()
+# Create a vecorfield for the wind
+windvector = parcels.VectorField("Wind", fieldset.UWind, fieldset.VWind)
+fieldset.add_field(windvector)
 ```
 
 Now we define a wind kernel that uses a forward Euler method to apply the wind forcing. Note that we update the `particles.dlon` and `particles.dlat` variables, rather than `particles.lon` and `particles.lat` directly.
 
 ```{code-cell}
 def wind_kernel(particles, fieldset):
-    particles.dlon += (
-        fieldset.UWind[particles] * particles.dt
-    )
-    particles.dlat += (
-        fieldset.VWind[particles] * particles.dt
-    )
+    uwind, vwind = fieldset.Wind[particles]
+    particles.dlon += uwind * particles.dt
+    particles.dlat += vwind * particles.dt
 ```
 
 First run a simulation where we apply kernels as `[AdvectionRK4, wind_kernel]`

docs/user_guide/examples/tutorial_dt_integrators.ipynb

@@ -123,8 +123,8 @@
     "U_max_surface = np.nanmax(np.hypot(ds_fields.uo, ds_fields.vo))\n",
     "print(f\"U_max = {str(np.round(U_max_surface, 2))} m s-1\")\n",
     "\n",
-    "# convert to degrees s-1 (at lat = 30 deg S, lon = 31 deg E)\n",
-    "U_max_surface_deg = parcels.GeographicPolar().to_target(U_max_surface, 0, -30, 31)\n",
+    "# convert to degrees s-1 (at lat = 30 deg S)\n",
+    "U_max_surface_deg = U_max_surface / (1852 * 60 * np.cos(np.deg2rad(-30)))\n",
     "print(f\"      == {str(np.round(U_max_surface_deg * 1e5, 2))}e-5 degrees s-1\")"
    ]
   },
@@ -135,7 +135,7 @@
    "source": [
     "```{admonition} 🖥️ Spherical grids and unit converters\n",
     ":class: seealso\n",
-    "Our displacement occurs in units of longitude and latitde, but our velocity field is in m/s. Read the [UnitConversion guide](./tutorial_unitconverters.ipynb) to see how Parcels uses `parcels.GeographicPolar()` under the hood to convert from m s<sup>-1</sup> to degrees s<sup>-1</sup>.\n",
+    "Our displacement occurs in units of longitude and latitde, but our velocity field is in m/s. That's why we have to convert the units of velocity from m/s to degrees/s. In Parcels, this is done automatically for `VectorFields` when using a `spherical` grid. See the [UnitConversion guide](./tutorial_unitconverters.ipynb) guide for more information.\n",
     "```"
    ]
   },
@@ -822,7 +822,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "test-notebooks",
+   "display_name": "docs",
    "language": "python",
    "name": "python3"
   },
@@ -836,7 +836,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.13.9"
+   "version": "3.14.2"
   }
  },
  "nbformat": 4,

docs/user_guide/examples/tutorial_nemo_curvilinear.ipynb

@@ -97,10 +97,6 @@
     "V = parcels.Field(\n",
     "    \"V\", ds_fields[\"V\"], grid, interp_method=parcels.interpolators.XLinear\n",
     ")\n",
-    "U.units = parcels.GeographicPolar()\n",
-    "V.units = (\n",
-    "    parcels.GeographicPolar()\n",
-    ")  # U and V need GeographicPolar for  C-Grid interpolation to work correctly\n",
     "UV = parcels.VectorField(\n",
     "    \"UV\", U, V, vector_interp_method=parcels.interpolators.CGrid_Velocity\n",
     ")\n",