NetCDF meteo variable must be last in file structure, otherwise cryptic error

[moritzshore]

Hi, I was busy trying to convert Meteo data from MetNordic to a CWatM compatible format, and I found a quirk in the CWatM code that could be perhaps adjusted to make it more clear whats going wrong:

Essentally, I used R package terra and functions project() and writeCDF() to reproject the MetNordic provided .nc file. This function writeCDF() function appends a "crs" variable onto the file.

     2 variables (excluding dimension variables):
        float precipitation_amount_sum[easting,northing,time]   (Contiguous storage)  
            units: kg/m^2
            _FillValue: -1.17549402418441e+38
            grid_mapping: crs
        int crs[]   (Contiguous storage)  

I then edited the file to replace the "easting" and "northing" with "x" and "y" (otherwise the CWatM code would break, due to line 982 perhaps?:

CWatM/cwatm/management_modules/data_handling.py

Line 982 in 31ed493

if value in ["X", "Y", "x", "y", "lon", "lat", "time"]:

After that I figured I was ready to feed the file to CWatM, but got a cryptic error message:

File "C:\Users\mosh\Documents\GIT\CWatM\cwatm\management_modules\data_handling.py", line 989, in multinetdf
    shapey = nf1.variables[value].shape[1]
             ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^
IndexError: tuple index out of range

The reason for the error turns out to be that it takes the last variable from the netCDF file:

CWatM/cwatm/management_modules/data_handling.py

Line 981 in 31ed493

value = list(nf1.variables.items())[-1][0] # get the last variable name

...which in my case was crs and does not have x and y definitions in .shape[1]. Reversing the order of the variables to have crs first and precipitation_amount_sum last fixed the issue.

This could be improved by dropping dimensionless variables, or perhaps an error message explaning the issue?

Its also totally possible that I just totally missed some sort of documentation specifying these requirements....

Anyway, just thought I'd mention it, in case it interests you..