Source code for

#!/usr/bin/env python
# Copyright (c) 2011-2023, wradlib developers.
# Distributed under the MIT License. See LICENSE.txt for more info.

NetCDF Data I/O
Former available xarray based code has been ported to `xradar <>`__-package.

.. autosummary::
   :toctree: generated/

__all__ = [

__doc__ = __doc__.format("\n   ".join(__all__))

import collections
import contextlib
import datetime as dt

import numpy as np

from wradlib.util import import_optional

nc = import_optional("netCDF4")

def _open_netcdf(filename):
    if isinstance(filename, str):
        yield nc.Dataset(filename)
        yield nc.Dataset("name", mode="r",

[docs]def read_edge_netcdf(filename, *, enforce_equidist=False): """Data reader for netCDF files exported by the EDGE radar software The corresponding NetCDF files from the EDGE software typically contain only one variable (e.g. reflectivity) for one elevation angle (sweep). The elevation angle is specified in the attributes keyword "Elevation". Please note that the radar might not return data with equidistant azimuth angles. In case you need equidistant azimuth angles, please set enforce_equidist to True. Parameters ---------- filename : str or file-like path of the netCDF file or file-like object enforce_equidist : bool Set True if the values of the azimuth angles should be forced to be equidistant; default value is False Returns ------- output : tuple Array of image data (dBZ), dictionary of attributes """ with _open_netcdf(filename) as dset: data = dset.variables[dset.TypeName][:] # Check azimuth angles and rotate image az = dset.variables["Azimuth"][:] # These are the indices of the minimum and maximum azimuth angle ix_minaz = np.argmin(az) ix_maxaz = np.argmax(az) if enforce_equidist: az = np.linspace( np.round(az[ix_minaz], 2), np.round(az[ix_maxaz], 2), len(az) ) else: az = np.roll(az, -ix_minaz) # rotate accordingly data = np.roll(data, -ix_minaz, axis=0) data = np.where(data == dset.getncattr("MissingData"), np.nan, data) # Ranges binwidth = (dset.getncattr("MaximumRange-value") * 1000.0) / len( dset.dimensions["Gate"] ) r = np.arange( binwidth, (dset.getncattr("MaximumRange-value") * 1000.0) + binwidth, binwidth, ) # collect attributes attrs = {} for attrname in dset.ncattrs(): attrs[attrname] = dset.getncattr(attrname) # Set additional metadata attributes attrs["az"] = az attrs["r"] = r attrs["site"] = (attrs["Longitude"], attrs["Latitude"], attrs["Height"]) attrs["time"] = dt.datetime.utcfromtimestamp(attrs.pop("Time")) attrs["max_range"] = data.shape[1] * binwidth return data, attrs
def read_netcdf_group(ncid): """Reads netcdf (nested) groups into python dictionary with corresponding structure. Note ---- The returned dictionary could be quite big, depending on the content of the file. Parameters ---------- ncid : object nc/group id from netcdf file Returns ------- out : dict an ordered dictionary that contains both data and metadata according to the original netcdf file structure """ out = collections.OrderedDict() # attributes for k, v in ncid.__dict__.items(): out[k] = v # groups if ncid.groups: for k, v in ncid.groups.items(): out[k] = read_netcdf_group(v) # dimensions dimids = np.array([]) if ncid.dimensions: dim = collections.OrderedDict() for k, v in ncid.dimensions.items(): tmp = collections.OrderedDict() try: tmp["data_model"] = v._data_model except AttributeError: pass try: tmp["size"] = v.__len__() except AttributeError: pass tmp["dimid"] = v._dimid dimids = np.append(dimids, v._dimid) tmp["grpid"] = v._grpid tmp["isunlimited"] = v.isunlimited() dim[k] = tmp # Usually, the dimensions should be ordered by dimid automatically # in case netcdf used OrderedDict. However, we should doublecheck if np.array_equal(dimids, np.sort(dimids)): # is already sorted out["dimensions"] = dim else: # need to sort dim2 = collections.OrderedDict() keys = dim.keys() for dimid in np.sort(dimids): dim2[keys[dimid]] = dim[keys[dimid]] out["dimensions"] = dim2 # variables if ncid.variables: var = collections.OrderedDict() for k, v in ncid.variables.items(): tmp = collections.OrderedDict() for k1 in v.ncattrs(): tmp[k1] = v.getncattr(k1) if v[:].dtype.kind == "S": try: tmp["data"] = nc.chartostring(v[:]) except Exception: tmp["data"] = v[:] else: tmp["data"] = v[:] var[k] = tmp out["variables"] = var return out
[docs]def read_generic_netcdf(fname): """Reads netcdf files and returns a dictionary with corresponding structure. In contrast to other file readers under :mod:``, this function will *not* return a two item tuple with (data, metadata). Instead, this function returns ONE dictionary that contains all the file contents - both data and metadata. The keys of the output dictionary conform to the Group/Subgroup directory branches of the original file. Please see the examples below on how to browse through a return object. The most important keys are the "dimensions" which define the shape of the data arrays, and the "variables" which contain the actual data and typically also the data that define the dimensions (e.g. sweeps, azimuths, ranges). These keys should be present in any netcdf file. Note ---- The returned dictionary could be quite big, depending on the content of the file. Parameters ---------- fname : str or file-like a netcdf file path or file-like object Returns ------- out : dict an ordered dictionary that contains both data and metadata according to the original netcdf file structure Examples -------- See :ref:`/notebooks/fileio/legacy/read_netcdf.ipynb`. """ with _open_netcdf(fname) as ncid: out = read_netcdf_group(ncid) return out