Error reading NetCDF file dimensions with units degrees #4460
Description
🐛 Bug Report
(Edited to show the error is associated with the coordinates having units 'degrees' rather than no units.)
I can create a NetCDF file of a field with 'longitude' and 'latitude' coordinates with units 'degrees' using the netCDF4 module version 1.5.8. Its metadata appears correct according to ncdump and the data it contains looks correct according to ncview. When I read the file using iris 3.1.0, however, it assigns the name 'grid_latitude' to both coordinates.
How To Reproduce
Steps to reproduce the behaviour:
Creating the file, reading it in with iris and printing the cube:
import numpy as np
import iris
import netCDF4
lat_vals=np.arange(-90,90)
lon_vals=np.arange(360)
data_out=np.random.normal(0,1,(len(lat_vals),len(lon_vals)))
fname='test.nc'
f = netCDF4.Dataset(fname, 'w')
lat_dim=f.createDimension('latitude', len(lat_vals))
lats=f.createVariable('latitude', 'f4', ('latitude',))
lats[:]=lat_vals
lon_dim=f.createDimension('longitude', len(lon_vals))
lons=f.createVariable('longitude', 'f4', ('longitude',))
lons[:]=lon_vals
data=f.createVariable('data', 'f4', ('latitude','longitude'))
data[:]=data_out
#Commenting these next two lines makes iris read the file correctly
lats.units='degrees'
lons.units='degrees'
f.close()
cube=iris.load_cube(fname)
print(cube)
This gives the result
data / (unknown) (grid_latitude: 180; grid_latitude: 360)
Dimension coordinates:
grid_latitude x -
grid_latitude - x
Expected behaviour
That iris would name the coordinates "latitude" and "longitude".
Environment
- OS & Version: CentOS Linux 7
- Iris Version: 3.1.0