chore: Convert xarray variables to numpy arrays for consistent operat…

…ions in kinematics.velocity_from_position and kinematics.position_from_velocity (Cloud-Drift#443)

clouddrift/kinematics.py

@@ -659,6 +659,15 @@ def velocity_from_position(
     y_ = np.swapaxes(y, time_axis, -1)
     time_ = np.swapaxes(time, time_axis, -1)
 
+    # Convert to numpy arrays to insure consistent operations
+    if isinstance(x_, xr.DataArray):
+        x_ = x_.to_numpy()
+    if isinstance(y_, xr.DataArray):
+        y_ = y_.to_numpy()
+    if isinstance(time_, xr.DataArray):
+        time_ = time_.to_numpy()
+
+    # Initialize arrays for dx, dy, and dt
     dx = np.empty(x_.shape)
     dy = np.empty(y_.shape)
     dt = np.empty(time_.shape)

tests/kinematics_tests.py

@@ -275,7 +275,7 @@ def test_velocity_position_roundtrip_centered(self):
         self.assertTrue(np.allclose(lon, self.lon, atol=1e-2))
         self.assertTrue(np.allclose(lat, self.lat, atol=1e-2))
 
-    def test_works_with_xarray(self):
+    def test_works_with_xarray_forward(self):
         lon, lat = position_from_velocity(
             xr.DataArray(data=self.uf),
             xr.DataArray(data=self.vf),
@@ -287,6 +287,30 @@ def test_works_with_xarray(self):
         self.assertTrue(np.allclose(lon, self.lon))
         self.assertTrue(np.allclose(lat, self.lat))
 
+    def test_works_with_xarray_backward(self):
+        lon, lat = position_from_velocity(
+            xr.DataArray(data=self.ub),
+            xr.DataArray(data=self.vb),
+            xr.DataArray(data=self.time),
+            self.lon[0],
+            self.lat[0],
+            integration_scheme="backward",
+        )
+        self.assertTrue(np.allclose(lon, self.lon))
+        self.assertTrue(np.allclose(lat, self.lat))
+
+    def test_works_with_xarray_centered(self):
+        lon, lat = position_from_velocity(
+            xr.DataArray(data=self.uc),
+            xr.DataArray(data=self.vc),
+            xr.DataArray(data=self.time),
+            self.lon[0],
+            self.lat[0],
+            integration_scheme="centered",
+        )
+        self.assertTrue(np.allclose(lon, self.lon, atol=1e-2))
+        self.assertTrue(np.allclose(lat, self.lat, atol=1e-2))
+
     def test_works_with_2d_array(self):
         uf = np.reshape(np.tile(self.uf, 4), (4, self.uf.size))
         vf = np.reshape(np.tile(self.vf, 4), (4, self.vf.size))
@@ -388,14 +412,30 @@ def test_result_value(self):
         self.assertTrue(np.all(np.isclose(self.ub, u_expected)))
         self.assertTrue(np.all(np.isclose(self.uc, u_expected)))
 
-    def test_works_with_xarray(self):
+    def test_works_with_xarray_forward(self):
         lon = xr.DataArray(data=self.lon, coords={"time": self.time})
         lat = xr.DataArray(data=self.lat, coords={"time": self.time})
         time = xr.DataArray(data=self.time, coords={"time": self.time})
-        uf, vf = velocity_from_position(lon, lat, time)
+        uf, vf = velocity_from_position(lon, lat, time, difference_scheme="forward")
         self.assertTrue(np.all(uf == self.uf))
         self.assertTrue(np.all(vf == self.vf))
 
+    def test_works_with_xarray_backward(self):
+        lon = xr.DataArray(data=self.lon, coords={"time": self.time})
+        lat = xr.DataArray(data=self.lat, coords={"time": self.time})
+        time = xr.DataArray(data=self.time, coords={"time": self.time})
+        ub, vb = velocity_from_position(lon, lat, time, difference_scheme="backward")
+        self.assertTrue(np.all(ub == self.ub))
+        self.assertTrue(np.all(vb == self.vb))
+
+    def test_works_with_xarray_centered(self):
+        lon = xr.DataArray(data=self.lon, coords={"time": self.time})
+        lat = xr.DataArray(data=self.lat, coords={"time": self.time})
+        time = xr.DataArray(data=self.time, coords={"time": self.time})
+        uc, vc = velocity_from_position(lon, lat, time, difference_scheme="centered")
+        self.assertTrue(np.all(uc == self.uc))
+        self.assertTrue(np.all(vc == self.vc))
+
     def test_works_with_2d_array(self):
         lon = np.reshape(np.tile(self.lon, 4), (4, self.lon.size))
         lat = np.reshape(np.tile(self.lat, 4), (4, self.lat.size))