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Python interface to map GRIB files to the NetCDF Common Data Model following the CF Convention using ecCodes.

Project description

Python interface to map GRIB files to the NetCDF Common Data Model following the CF Conventions. The high level API is designed to support a GRIB backend for xarray and it is inspired by NetCDF-python and h5netcdf. Low level access and decoding is performed via the ECMWF ecCodes library.

Features:

  • map a GRIB file to a set of N-dimensional variables following the NetCDF Common Data Model,
  • map CF Conventions attributes coordinate and data variables,
  • access data variable values from disk efficiently,
  • provisional xarray GRIB driver,
  • no write support yet.

Installation

The package is installed from PyPI with:

$ pip install cfgrib

System dependencies

The python module depends on the ECMWF ecCodes library that must be installed on the system and accessible as a shared library. Some Linux distributions ship a binary version of ecCodes that may be installed with the standard package manager. On Ubuntu 18.04 use the command:

$ sudo apt-get install libeccodes0

On a MacOS with HomeBrew use:

$ brew install eccodes

As an alternative you may install the official source distribution by following the ecCodes instructions at https://software.ecmwf.int/wiki/display/ECC/ecCodes+installation

Note that ecCodes support for the Windows operating system is experimental.

You may run a simple self-check command to ensure that your system is set up correctly:

$ python -m cfgrib --selfcheck
Found: ecCodes v2.7.0.
Your system is ready.

Usage

First, you need a well-formed GRIB file, if you don’t have one at hand you can download our ERA5 on pressure levels sample:

$ wget http://download.ecmwf.int/test-data/cfgrib/era5-levels-members.grib

Dataset / Variable API

You may try out the high level API in a python interpreter:

>>> import cfgrib
>>> ds = cfgrib.Dataset.frompath('era5-levels-members.grib')
>>> ds.attributes['GRIB_edition']
1
>>> ds.dimensions.items()
[('number', 10), ('forecast_reference_time', 4), ('air_pressure', 2), ('latitude', 61), ('longitude', 120)]
>>> sorted(ds.variables)
['air_pressure', 'forecast_period', 'forecast_reference_time', 'latitude', 'longitude', 'number', 't', 'time', 'z']
>>> var = ds.variables['t']
>>> var.dimensions
('number', 'forecast_reference_time', 'air_pressure', 'latitude', 'longitude')
>>> var.data[:, :, :, :, :].mean()
262.92133

Provisional xarray GRIB driver

If you have xarray installed cfgrib can open a GRIB file as a xarray.Dataset:

$ pip install xarray

In a Python interpreter try:

>>> from cfgrib import xarray_store
>>> ds = xarray_store.open_dataset('era5-levels-members.grib')
>>> ds
<xarray.Dataset>
Dimensions:     (latitude: 61, level: 2, longitude: 120, number: 10, time: 4)
Coordinates:
  * number      (number) int64 0 1 2 3 4 5 6 7 8 9
  * time        (time) datetime64[ns] 2017-01-01 2017-01-01T12:00:00 ...
    step        timedelta64[ns] ...
  * level       (level) float64 8.5e+04 5e+04
  * latitude    (latitude) float64 90.0 87.0 84.0 81.0 78.0 75.0 72.0 69.0 ...
  * longitude   (longitude) float64 0.0 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0 ...
    valid_time  (time) datetime64[ns] ...
Data variables:
    z           (number, time, level, latitude, longitude) float32 ...
    t           (number, time, level, latitude, longitude) float32 ...
Attributes:
    GRIB_edition:            1
    GRIB_centre:             ecmf
    GRIB_centreDescription:  European Centre for Medium-Range Weather Forecasts
    GRIB_subCentre:          0
    GRIB_table2Version:      128
    history:                 GRIB to CDM+CF via cfgrib-0.8.0/ecCodes-2.7.0

Lower level APIs

Lower level APIs are not stable and should not be considered public yet. In particular the internal Python 3 ecCodes bindings are not compatible with the standard ecCodes python module.

Contributing

Contributions are very welcome. Please see the CONTRIBUTING.rst document for the best way to help. If you encounter any problems, please file an issue along with a detailed description.

Lead developer:

Main contributors:

See also the list of contributors who participated in this project.

License

Copyright 2017-2018 European Centre for Medium-Range Weather Forecasts (ECMWF).

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0. Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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