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No latitudes/longitudes provided by ecCodes for gridType #28

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alexamici opened this Issue Nov 7, 2018 · 1 comment

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alexamici commented Nov 7, 2018

cfgrib relies on the ECMWF ecCodes C-library for encoding and decoding the GRIB format, including everything related to the coordinate systems. GRIB files encoded in a gridType not supported by the installed ecCodes version will print the warning: No latitudes/longitudes provided by ecCodes for gridType.

The GRIB file will be opened but the geographic portion of the data will be represented by as single dimension without coordinate named values.

For example:

>>> cfgrib.open_dataset('../ST4.2018080204.01h')
No latitudes/longitudes provided by ecCodes for gridType = 'polar_stereographic'
<xarray.Dataset>
Dimensions:     (values: 987601)
Coordinates:
    time        datetime64[ns] ...
    step        timedelta64[ns] ...
    surface     int64 ...
    valid_time  datetime64[ns] ...
Dimensions without coordinates: values
Data variables:
    tp          (values) float32 ...
Attributes:
    GRIB_edition:            1
    GRIB_centre:             kwbc
    GRIB_centreDescription:  US National Weather Service - NCEP 
    GRIB_subCentre:          4
    history:                 GRIB to CDM+CF via cfgrib-0.9.../ecCodes-2.8...

The list of known supported gridTypes is:

  • latitude and longitude as dimension coordinates
    • regular_ll
    • regular_gg
  • xand y as dimensions and latitude and longitude as non-dimension coordinates
    • rotated_ll
    • rotated_gg
    • lambert
    • polar_stereographic (ecCodes > 2.9.0)
  • values as dimension and latitude and longitude as non-dimension coordinates
    • reduced_ll
    • reduced_gg
    • unstructured_grid

see http://xarray.pydata.org/en/stable/data-structures.html#coordinates for details on xarray naming conventions.

Initially noted in #27.

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alexamici commented Nov 7, 2018

The reason the issue is labeled wontfix is that cfgrib is not designed to handle coordinate systems and we can just wait for ecCodes to add support for new gridTypes.

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