Accessors#

To extend xarray.DataArray and xarray.Dataset xradar aims to provide accessors which downstream libraries can hook into.

Those accessors are yet to be defined. For starters we could implement purpose-based accessors (like .vis, .kdp or .trafo) on xarray.DataArray level.

To not have to import downstream packages a similar approach to xarray.backends using importlib.metadata.entry_points could be facilitated.

In this notebook the creation of such an accessor is showcased.

[1]:

import numpy as np
import xarray as xr
from open_radar_data import DATASETS

import xradar as xd

Import Data#

Fetch data from open-radar-data repository.

[2]:

filename = DATASETS.fetch("71_20181220_060628.pvol.h5")

Downloading file '71_20181220_060628.pvol.h5' from 'https://github.com/openradar/open-radar-data/raw/main/data/71_20181220_060628.pvol.h5' to '/home/docs/.cache/open-radar-data'.

Open data#

[3]:

ds = xr.open_dataset(filename, group="sweep_0", engine="odim")
display(ds.DBZH.values)

array([[ nan,  0. , 13. , ...,  nan,  nan,  nan],
       [ nan,  1.5, 13.5, ...,  nan,  nan,  nan],
       [ nan,  1.5, 11.5, ...,  nan,  nan,  nan],
       ...,
       [ nan,  1.5, 11.5, ...,  nan,  nan,  nan],
       [ nan,  1.5,  6. , ...,  nan,  nan,  nan],
       [ nan,  6. , 12.5, ...,  nan,  nan,  nan]], shape=(360, 1200))

Plot DBZH#

[4]:

ds.DBZH.plot()

Matplotlib is building the font cache; this may take a moment.

[4]:

<matplotlib.collections.QuadMesh at 0x7fd7aa83fa10>

Define two example functions#

Functions copied verbatim from wradlib.

[5]:

def _decibel(x):
    """Calculates the decibel representation of the input values

    :math:`dBZ=10 \\cdot \\log_{10} z`

    Parameters
    ----------
    x : float or :class:`numpy:numpy.ndarray`
        (must not be <= 0.)

    Examples
    --------
    >>> from wradlib.trafo import decibel
    >>> print(decibel(100.))
    20.0
    """
    return 10.0 * np.log10(x)


def _idecibel(x):
    """Calculates the inverse of input decibel values

    :math:`z=10^{x \\over 10}`

    Parameters
    ----------
    x : float or :class:`numpy:numpy.ndarray`

    Examples
    --------
    >>> from wradlib.trafo import idecibel
    >>> print(idecibel(10.))
    10.0

    """
    return 10.0 ** (x / 10.0)

Function dictionaries#

To show the import of the functions, we put them in different dictionaries as we would get them via entry_points.

This is what the downstream libraries would have to provide.

[6]:

package_1_func = {"trafo": {"decibel": _decibel}}
package_2_func = {"trafo": {"idecibel": _idecibel}}

xradar internal functionality#

This is how xradar would need to treat that input data.

[7]:

downstream_functions = [package_1_func, package_2_func]
xradar_accessors = ["trafo"]

[8]:

package_functions = {}
for accessor in xradar_accessors:
    package_functions[accessor] = {}
    for dfuncs in downstream_functions:
        package_functions[accessor].update(dfuncs[accessor])
print(package_functions)

{'trafo': {'decibel': <function _decibel at 0x7fd7a957cd60>, 'idecibel': <function _idecibel at 0x7fd7a957ce00>}}

Create and register accessor#

We bundle the different steps into one function, create_xradar_dataarray_accessor.

[9]:

for accessor in xradar_accessors:
    xd.accessors.create_xradar_dataarray_accessor(accessor, package_functions[accessor])

Convert DBZH to linear and plot#

[10]:

z = ds.DBZH.trafo.idecibel()
z.plot()

[10]:

<matplotlib.collections.QuadMesh at 0x7fd7a95044d0>