MNT: Avoid some unit stripped warnings from cross-section

src/metpy/calc/cross_sections.py

@@ -123,8 +123,8 @@ def unit_vectors_from_cross_section(cross, index='index'):
 
     """
     x, y = distances_from_cross_section(cross)
-    dx_di = first_derivative(x, axis=index).values
-    dy_di = first_derivative(y, axis=index).values
+    dx_di = first_derivative(x, axis=index).data
+    dy_di = first_derivative(y, axis=index).data
     tangent_vector_mag = np.hypot(dx_di, dy_di)
     unit_tangent_vector = np.vstack([dx_di / tangent_vector_mag, dy_di / tangent_vector_mag])
     unit_normal_vector = np.vstack([-dy_di / tangent_vector_mag, dx_di / tangent_vector_mag])

src/metpy/interpolate/slices.py

@@ -7,7 +7,6 @@
 import xarray as xr
 
 from ..package_tools import Exporter
-from ..units import is_quantity, units
 from ..xarray import check_axis
 
 exporter = Exporter(globals())
@@ -50,17 +49,14 @@ def interpolate_to_slice(data, points, interp_type='linear'):
                          'your data has been parsed by MetPy with proper x and y '
                          'dimension coordinates.') from None
 
+    data = data.metpy.dequantify()
     data_sliced = data.interp({
         x.name: xr.DataArray(points[:, 0], dims='index', attrs=x.attrs),
         y.name: xr.DataArray(points[:, 1], dims='index', attrs=y.attrs)
     }, method=interp_type)
     data_sliced.coords['index'] = range(len(points))
 
-    # Bug in xarray: interp strips units
-    if is_quantity(data.data) and not is_quantity(data_sliced.data):
-        data_sliced.data = units.Quantity(data_sliced.data, data.data.units)
-
-    return data_sliced
+    return data_sliced.metpy.quantify()
 
 
 @exporter.export

tests/calc/test_indices.py

@@ -158,7 +158,7 @@ def test_weighted_continuous_average_elevated():
 def test_precipitable_water_xarray():
     """Test precipitable water with xarray input."""
     data = get_upper_air_data(datetime(2016, 5, 22, 0), 'DDC')
-    press = xr.DataArray(data['pressure'], attrs={'units': str(data['pressure'].units)})
+    press = xr.DataArray(data['pressure'].m, attrs={'units': str(data['pressure'].units)})
     dewp = xr.DataArray(data['dewpoint'], dims=('press',), coords=(press,))
     pw = precipitable_water(press, dewp, top=400 * units.hPa)
     truth = 22.60430651 * units.millimeters