Problem with cross section

[oki36]

Hiii..
I'm new using python and want to make a cross section of my radar data. I'm not sure why my script is not working:

fn="2v-mlitradar_2022-06-03_0450utc.nc"
datapath="./"

time = fn[13:28]
data = xr.open_dataset(datapath+fn)
data = data.metpy.parse_cf().squeeze()

print(data)

colorscale = "pyart_NWSRef"

start = (139.5, 35.8)
end = (139.5, 36.3)

cross = cross_section(data, start, end)
print(cross)

cross.set_coords(('lat','lon'),True)
print(cross)

#Define the figure object and primary axes
fig = plt.figure(1, figsize=(16., 9.))
ax = plt.axes()

#plot 
re_contour = ax.contourf( cross['lon'],cross['REF'],
                         levels=np.arange(-10, 60, .05), cmap=colorscale)
re_colorbar = fig.colorbar(re_contour)

plt.show()

I'm getting:

  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\metpy\interpolate\slices.py", line 162, in cross_section
    x = data.metpy.x
  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\metpy\xarray.py", line 502, in x
    return self._axis('x')
  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\metpy\xarray.py", line 419, in _axis
    raise AttributeError(axis + ' attribute is not available.')
AttributeError: x attribute is not available.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "pruebita.py", line 32, in <module>
    cross = cross_section(data, start, end)
  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\metpy\interpolate\slices.py", line 151, in cross_section
    return data.map(cross_section, True, (start, end), steps=steps,
  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\xarray\core\dataset.py", line 5934, in map
    variables = {
  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\xarray\core\dataset.py", line 5935, in <dictcomp>
    k: maybe_wrap_array(v, func(v, *args, **kwargs))
  File "C:\Users\anaconda3\envs\pyart_env\lib\site-packages\metpy\interpolate\slices.py", line 164, in cross_section
    raise ValueError('Data missing required coordinate information. Verify that '
ValueError: Data missing required coordinate information. Verify that your data have been parsed by MetPy with proper x and y dimension coordinates and added crs coordinate of the correct projection for each variable.

[DanielAdriaansen]

Thank you for sharing your code and your full error message. In the error message, it looks like this is the main problem with the current error:
AttributeError: x attribute is not available.

From the documentation for cross_section:

must have been parsed by MetPy and include both an x and y coordinate dimension and the added crs coordinate.

It would seem that your cross variable does not include x and y coordinate dimensions based on the error but I can't be sure without seeing the output from your print statements.

Could you share the output of the three print statements in your above code?

[oki36]

Is there a way to say that my x and y coordinate are lat and lon? because they're the same.

I only have the first print, because then it has error.

First print :

**<xarray.Dataset>
Dimensions: (ALT: 41, LAT: 571, LON: 457)
Coordinates:

• ALT (ALT) float64 0.0 250.0 500.0 ... 9.5e+03 9.75e+03 1e+04
  TIME datetime64[ns] 2022-06-03T06:00:00
• LAT (LAT) float64 34.6 34.6 34.61 34.61 ... 37.16 37.16 37.16
• LON (LON) float64 138.4 138.4 138.4 138.4 ... 140.9 140.9 140.9
  metpy_crs object Projection: latitude_longitude
  Data variables:
  U (ALT) float32 ...
  V (ALT) float32 ...
  REF (ALT, LAT, LON) float32 ...
  ZDR (ALT, LAT, LON) float32 ...
  RHOHV (ALT, LAT, LON) float32 ...
  KDP (ALT, LAT, LON) float32 ...
  RR (ALT, LAT, LON) float32 ...
  QUALITY_FLAGS (ALT, LAT, LON) int16 ...
  Attributes:
  Conventions: COARDS
  institution: National Research Institute..
  xnet_product: 2v-mlitradar
  creator: radar3d version 0.8
  history: Fri Jun 3 15:04:21 2022**

[DanielAdriaansen]

Based on this #949 (comment):

Try including the specific variable you'd like to make the cross-section for. If you are trying to make a reflectivity cross section, then change this line:
cross = cross_section(data, start, end)
to be:
cross = cross_section(data['REF'], start, end)

And see if that works.

The trouble I think is that variables U and V do not have LAT and LON coordinate variables, and so cross_section fails when passing the whole dataset.

If you want multiple variables, you can do:
cross = cross_section(data[['REF','ZDR','RHOHV','KDP','RR','QUALITY_FLAGS']], start, end)

Just make sure any variable you're passing to cross_section has LAT and LON coordinates.