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.

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.

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

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

ds.DBZH.plot()

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

<matplotlib.collections.QuadMesh at 0x7c7e83aa6510>

Define two example functions

Functions copied verbatim from wradlib.

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.

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.

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

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 0x7c7e828dcd60>, 'idecibel': <function _idecibel at 0x7c7e828dce00>}}

Create and register accessor

We bundle the different steps into one function, create_xradar_dataarray_accessor.

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

Convert DBZH to linear and plot

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

<matplotlib.collections.QuadMesh at 0x7c7e828f6710>

Convert z to decibel and plot()

dbz = z.trafo.decibel()
display(dbz)

<xarray.DataArray 'DBZH' (azimuth: 360, range: 1200)> Size: 3MB
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))
Coordinates:
  * azimuth    (azimuth) float32 1kB 0.5 1.5 2.5 3.5 ... 356.5 357.5 358.5 359.5
    elevation  (azimuth) float64 3kB ...
    time       (azimuth) datetime64[ns] 3kB ...
  * range      (range) float32 5kB 125.0 375.0 625.0 ... 2.996e+05 2.999e+05
    longitude  float64 8B ...
    latitude   float64 8B ...
    altitude   float64 8B ...
Attributes:
    _Undetect:      0.0
    standard_name:  radar_equivalent_reflectivity_factor_h
    long_name:      Equivalent reflectivity factor H
    units:          dBZ

xarray.DataArray

'DBZH'

• azimuth: 360
• range: 1200

• nan 0.0 13.0 16.0 18.5 28.5 25.0 22.0 ... nan nan nan nan nan nan nan

  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))

• Coordinates: (7)
  • azimuth
    (azimuth)
    float32
    0.5 1.5 2.5 ... 357.5 358.5 359.5

    standard_name :

    ray_azimuth_angle

    long_name :

    azimuth_angle_from_true_north

    units :

    degrees

    axis :

    radial_azimuth_coordinate

    array([  0.5,   1.5,   2.5, ..., 357.5, 358.5, 359.5],
          shape=(360,), dtype=float32)

  • elevation
    (azimuth)
    float64
    ...

    standard_name :

    ray_elevation_angle

    long_name :

    elevation_angle_from_horizontal_plane

    units :

    degrees

    axis :

    radial_elevation_coordinate

    [360 values with dtype=float64]

  • time
    (azimuth)
    datetime64[ns]
    ...

    standard_name :

    time

    [360 values with dtype=datetime64[ns]]

  • range
    (range)
    float32
    125.0 375.0 ... 2.996e+05 2.999e+05

    units :

    meters

    standard_name :

    projection_range_coordinate

    long_name :

    range_to_measurement_volume

    axis :

    radial_range_coordinate

    meters_between_gates :

    250.0

    spacing_is_constant :

    true

    meters_to_center_of_first_gate :

    125.0

    array([1.25000e+02, 3.75000e+02, 6.25000e+02, ..., 2.99375e+05, 2.99625e+05,
           2.99875e+05], shape=(1200,), dtype=float32)

  • longitude
    ()
    float64
    ...

    long_name :

    longitude

    units :

    degrees_east

    standard_name :

    longitude

    [1 values with dtype=float64]

  • latitude
    ()
    float64
    ...

    long_name :

    latitude

    units :

    degrees_north

    positive :

    up

    standard_name :

    latitude

    [1 values with dtype=float64]

  • altitude
    ()
    float64
    ...

    long_name :

    altitude

    units :

    meters

    standard_name :

    altitude

    [1 values with dtype=float64]

• Attributes: (4)

  _Undetect :

  0.0

  standard_name :

  radar_equivalent_reflectivity_factor_h

  long_name :

  Equivalent reflectivity factor H

  units :

  dBZ

dbz.plot()

<matplotlib.collections.QuadMesh at 0x7c7e82e14b90>