Iris does not recognise x and y coordinates of netCDF files with rotated mercator projection #4830
Description
🐛 Bug Report
When loading a model that uses the rotated mercator projection, iris does not recognise the co-ordinate system and the resulting x and y coordinates of the iris cube are anonymous. No warnings or errors are printed.
How To Reproduce
Steps to reproduce the behaviour:
Load this file for example: /project/champ/data/cordex/output/SAM-44/ICTP/MOHC-HadGEM2-ES/historical/r1i1p1/RegCM4-3/v4/day/pr/v20151029/pr_SAM-44_MOHC-HadGEM2-ES_historical_r1i1p1_ICTP-RegCM4-3_v4_day_1970010112-1975123012.nc
> c = iris.load_cube('/project/champ/data/cordex/output/SAM-44/ICTP/MOHC-HadGEM2-ES/historical/r1i1p1/R
...: egCM4-3/v4/day/pr/v20151029/pr_SAM-44_MOHC-HadGEM2-ES_historical_r1i1p1_ICTP-RegCM4-3_v4_day_197601011
...: 2-1980123012.nc')
> print(c)
precipitation_flux / (kg m-2 s-1) (time: 1800; -- : 199; -- : 189)
Dimension coordinates:
time x - -
Auxiliary coordinates:
latitude - x x
longitude - x x
Expected behaviour
The x and y co-ordinates of the cube should be recognised as the projection x and y coordinates and have the associated coordinate system metadata associated with them.
Environment
- OS & Version: RHEL7
- Iris Version: 3.1.0
Additional context
For info:
$ ncdump -h /project/champ/data/cordex/output/SAM-44/ICTP/MOHC-HadGEM2-ES/historical/r1i1p1/RegCM4-3/v4/day/pr/v20151029/pr_SAM-44_MOHC-HadGEM2-ES_historical_r1i1p1_ICTP-RegCM4-3_v4_day_1970010112-1975123012.nc
netcdf pr_SAM-44_MOHC-HadGEM2-ES_historical_r1i1p1_ICTP-RegCM4-3_v4_day_1970010112-1975123012 {
dimensions:
time = UNLIMITED ; // (2160 currently)
time_bnds = 2 ;
y = 199 ;
x = 189 ;
variables:
double time_bnds(time, time_bnds) ;
time_bnds:units = "days since 1949-12-01 00:00:00 UTC" ;
time_bnds:calendar = "360_day" ;
double lat(y, x) ;
lat:standard_name = "latitude" ;
lat:long_name = "Latitude at cross points" ;
lat:units = "degrees_north" ;
double lon(y, x) ;
lon:standard_name = "longitude" ;
lon:long_name = "Longitude at cross points" ;
lon:units = "degrees_east" ;
double x(x) ;
x:standard_name = "projection_x_coordinate" ;
x:long_name = "x-coordinate in Cartesian system" ;
x:units = "m" ;
x:axis = "X" ;
double y(y) ;
y:standard_name = "projection_y_coordinate" ;
y:long_name = "y-coordinate in Cartesian system" ;
y:units = "m" ;
y:axis = "Y" ;
int crs ;
crs:grid_mapping_name = "rotated_mercator" ;
crs:latitude_of_projection_origin = -22. ;
crs:longitude_of_projection_origin = -59. ;
crs:scale_factor_at_projection_origin = 1. ;
crs:semi_major_axis = 6371229. ;
crs:inverse_flattening = 0. ;
crs:_CoordinateTransformType = "Projection" ;
crs:_CoordinateAxisTypes = "GeoX GeoY" ;
crs:false_easting = -25000. ;
crs:false_northing = -25000. ;
double time(time) ;
time:standard_name = "time" ;
time:long_name = "time" ;
time:calendar = "360_day" ;
time:units = "days since 1949-12-01 00:00:00 UTC" ;
time:bounds = "time_bnds" ;
float pr(time, y, x) ;
pr:cell_methods = "time: mean" ;
pr:standard_name = "precipitation_flux" ;
pr:long_name = "Precipitation" ;
pr:units = "kg m-2 s-1" ;
pr:coordinates = "lat lon" ;
pr:grid_mapping = "crs" ;
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