Creating a CDF File

This module provides an example for creating a CDF File using the HermesData class. This class is an abstraction of underlying data structures to make the handling of measurement data easier when reading and writing CDF data.

>>> from collections import OrderedDict
>>> import numpy as np
>>> import astropy.units as u
>>> from astropy.timeseries import TimeSeries
>>> from astropy.nddata import NDData
>>> from astropy.wcs import WCS
>>> from ndcube import NDCube, NDCollection
>>> import tempfile
>>>
>>> # Import the `hermes_core` Package
>>> from hermes_core.timedata import HermesData
>>> from hermes_core.util.validation import validate
>>>
>>> # Create a np.ndarray of example measurement data
>>> bx = np.random.choice(a=[-1, 0, 1], size=1000).cumsum(0)
>>> by = np.random.choice(a=[-1, 0, 1], size=1000).cumsum(0)
>>>
>>> # Create a TimeSeries with the example measurement and a Time column
>>> ts = TimeSeries(
...     time_start="2016-03-22T12:30:31",
...     time_delta=3 * u.s,
...     data={"Bx GSE": u.Quantity(value=bx, unit="nanoTesla", dtype=np.int16)},
... )
>>>
>>> # You can also add new measurements to the TimeSeries directly
>>> ts.add_column(col=u.Quantity(value=by, unit="nanoTesla", dtype=np.int16),
...     name="By GSE"
... )
>>>
>>> # Create support data or non-time-varying (time invariant) data
>>> support_data = {
...     "data_mask": NDData(data=np.eye(100, 100, dtype=np.uint16))
... }
>>>
>>> # Create high-dimensional data leveraging the API of NDCube
>>> spectra = NDCollection(
...     [
...         (
...             "example_spectra",
...             NDCube(
...                 data=np.random.random(size=(4, 10)),
...                 wcs=WCS(naxis=2),
...                 meta={"CATDESC": "Example Spectra Variable"},
...                 unit="eV",
...             ),
...         )
...     ]
... )
>>>
>>> # To make the creation of global metadata easier you can use the static
>>> # `HermesData.global_attribute_template()` function.
>>> global_attrs_template = HermesData.global_attribute_template()
>>>
>>> global_attrs_template["DOI"] = "https://doi.org/<PREFIX>/<SUFFIX>"
>>> global_attrs_template["Data_level"] = "L1>Level 2"
>>> global_attrs_template["Data_version"] = "0.0.1"
>>> global_attrs_template[
...     "Descriptor"
... ] = "nemisis>Noise Eliminating Magnetometer Instrument in a Small Integrated System"
>>> global_attrs_template["Instrument_mode"] = "default"
>>> global_attrs_template["Instrument_type"] = "Magnetic Fields (space)"
>>> global_attrs_template["Data_product_descriptor"] = "odpd"
>>>
>>> global_attrs_template["HTTP_LINK"] = [
...     "https://science.nasa.gov/missions/hermes",
...     "https://github.com/HERMES-SOC",
...     "https://github.com/HERMES-SOC/hermes_nemisis",
... ]
>>> global_attrs_template["LINK_TEXT"] = ["HERMES homepage",
...     "HERMES SOC Github", "NEMISIS Analysis Tools"]
>>> global_attrs_template["LINK_TITLE"] = ["HERMES homepage",
...     "HERMES SOC Github", "NEMISIS Analysis Tools"]
>>>
>>> global_attrs_template["MODS"] = ["v0.0.1 - Original version."]
>>> global_attrs_template["PI_affiliation"] = "NASA Goddard Space Flight Center"
>>> global_attrs_template["PI_name"] = "Dr. Eftyhia Zesta"
>>> global_attrs_template["TEXT"] = "Sample HERMES NEMISIS CDF File"
>>>
>>> example_data = HermesData(
...     timeseries=ts,
...     support=support_data,
...     spectra=spectra,
...     meta=global_attrs_template
... )
>>>
>>> # To make the creation of variable metadata easier you can use the static
>>> # `HermesData.measurement_attribute_template()` function.
>>> template = HermesData.measurement_attribute_template()
>>>
>>> # Update the Metadata for each of the Measurements
>>> example_data.timeseries["Bx GSE"].meta.update(
...     OrderedDict({"CATDESC": "X component of magnetic Field GSE"}))
>>> example_data.timeseries["By GSE"].meta.update(
...     OrderedDict({"CATDESC": "Y component of magnetic Field GSE"}))
>>>
>>> # You can add new scalar time-variant measurements to the HermesData container
>>> bz = np.random.choice(a=[-1, 0, 1], size=1000).cumsum(0)
>>> example_data.add_measurement(
...     measure_name="Bz GSE",
...     data=u.Quantity(value=bz, unit="nanoTesla", dtype=np.int16),
...     meta={
...         "VAR_TYPE": "data",
...         "CATDESC": "Z component of magnetic Field GSE",
...     },
... )
>>>
>>> # You can add new time-invariant data to the HermesData container
>>> example_data.add_support(
...     name="calibration_const",
...     data=NDData(data=[1e-1]),
...     meta={
...         "CATDESC": "Calibration Factor",
...         "VAR_TYPE": "metadata"
...     },
... )
>>>
>>> # You can ass new spectral or high-dimensional data to the HermesData container
>>> data = NDCube(
...     data=np.random.random(size=(1000, 10)),
...     wcs=WCS(naxis=2),
...     meta={"CATDESC": "Example Spectra Variable"},
...     unit="eV",
... )
>>> example_data.add_spectra(
...     name="added_spectra",
...     data=data,
...     meta={"VAR_TYPE": "data"},
... )
>>>
>>> # create the CDF File
>>> DRYRUN=True
>>> if DRYRUN:
...     with tempfile.TemporaryDirectory() as tmpdirname:
...         cdf_file_path = example_data.save(output_path=tmpdirname)
... else:
...     cdf_file_path = example_data.save(output_path="./", overwrite=True)

The file that this code generates is made available as a sample file in this repository in hermes_core/data/sample/hermes_nms_default_l1_20160322T123031_v0.0.1.cdf.