Concatenated cubes lose their derived coordinate

[pelson]

I'm pretty deep into some code, and it looks like cube.concatenate is throwing away my derived coordinates. Apologies I can't provide a SSCCE currently (happy for this issue to simply be recorded until I get a chance to look into it).

[duncanwp]

I've hit this too, do you have an easy workaround?

[duncanwp]

Just adding one of the original aux factories to the concatenated Cube seems to work.

[bjlittle]

I'll take a peek ...

[bjlittle]

Yup, it's a known TODO, ever since concatenate was first written, see https://github.com/SciTools/iris/blob/v1.12.x/lib/iris/_concatenate.py#L40

[schlunma]

I just encountered the same problem in the latest version. Here is a working example:

import iris
print(iris.__version__)
print("")


# Load sample data
path = iris.sample_data_path('hybrid_height.nc')
cube_0 = iris.load(path)[0]

# Copy cube
cube_0.remove_coord('time')
cube_0 = iris.util.new_axis(cube_0)
cube_1 = cube_0.copy()
time_coord_0 = iris.coords.DimCoord([1],
                                    bounds=[0, 2],
                                    var_name='time',
                                    standard_name='time',
                                    long_name='time',
                                    units='days since 2000-01-01')
time_coord_1 = time_coord_0.copy([3], bounds=[2, 4])
cube_0.add_dim_coord(time_coord_0, 0)
cube_1.add_dim_coord(time_coord_1, 0)

print("Cubes have derived coordinate:")
print(cube_0)
print(cube_1)
print("")

# Concatenate
cubes = iris.cube.CubeList([cube_0, cube_1])
new_cube = cubes.concatenate_cube()
print("Cube does not have derived coordinate:")
print(new_cube)

which gives

2.3.0
Cubes have derived coordinate:
air_potential_temperature                    (time: 1; model_level_number: 15; grid_latitude: 100; grid_longitude: 100)
     Dimension coordinates:
          time                                    x                      -                  -                    -
          model_level_number                      -                      x                  -                    -
          grid_latitude                           -                      -                  x                    -
          grid_longitude                          -                      -                  -                    x
     Auxiliary coordinates:
          atmosphere_hybrid_height_coordinate     -                      x                  -                    -
          sigma                                   -                      x                  -                    -
          surface_altitude                        -                      -                  x                    x
     Derived coordinates:
          altitude                                -                      x                  x                    x
     Scalar coordinates:
          forecast_period: 0.0 hours
          forecast_reference_time: 2009-09-09 17:10:00
     Attributes:
          Conventions: CF-1.5
          STASH: m01s00i004
          source: Data from Met Office Unified Model 7.04
air_potential_temperature                    (time: 1; model_level_number: 15; grid_latitude: 100; grid_longitude: 100)
     Dimension coordinates:
          time                                    x                      -                  -                    -
          model_level_number                      -                      x                  -                    -
          grid_latitude                           -                      -                  x                    -
          grid_longitude                          -                      -                  -                    x
     Auxiliary coordinates:
          atmosphere_hybrid_height_coordinate     -                      x                  -                    -
          sigma                                   -                      x                  -                    -
          surface_altitude                        -                      -                  x                    x
     Derived coordinates:
          altitude                                -                      x                  x                    x
     Scalar coordinates:
          forecast_period: 0.0 hours
          forecast_reference_time: 2009-09-09 17:10:00
     Attributes:
          Conventions: CF-1.5
          STASH: m01s00i004
          source: Data from Met Office Unified Model 7.04

Cube does not have derived coordinate:
air_potential_temperature                    (time: 2; model_level_number: 15; grid_latitude: 100; grid_longitude: 100)
     Dimension coordinates:
          time                                    x                      -                  -                    -
          model_level_number                      -                      x                  -                    -
          grid_latitude                           -                      -                  x                    -
          grid_longitude                          -                      -                  -                    x
     Auxiliary coordinates:
          atmosphere_hybrid_height_coordinate     -                      x                  -                    -
          sigma                                   -                      x                  -                    -
          surface_altitude                        -                      -                  x                    x
     Scalar coordinates:
          forecast_period: 0.0 hours
          forecast_reference_time: 2009-09-09 17:10:00
     Attributes:
          Conventions: CF-1.5
          STASH: m01s00i004
          source: Data from Met Office Unified Model 7.04

I would be really nice of someone could take a look at this. Thanks! @bjlittle

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[schlunma]

Still an important issue for me (and ESMValTool development team).

[schlunma]

Just opened a PR that fixes this: #5096