.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "examples/plot_auto_grid.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_examples_plot_auto_grid.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_examples_plot_auto_grid.py:


Automatic SECS grid generation
-------------------------------

Choosing a SECS grid by hand means picking a spacing, a padding margin
around the stations, and checking that no pole lands on top of a
station. :meth:`pysecs.SECS.from_observations` (built on
:func:`pysecs.make_grid`) automates this from the observation network
alone: the spacing defaults to the median nearest-neighbor station
separation and the grid is padded several cells beyond the station
footprint so that currents just outside the network do not alias onto
the grid edges.

.. GENERATED FROM PYTHON SOURCE LINES 14-68



.. image-sg:: /examples/images/sphx_glr_plot_auto_grid_001.png
   :alt: Auto-generated grid: fitted horizontal current density
   :srcset: /examples/images/sphx_glr_plot_auto_grid_001.png
   :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    auto-generated grid: 195 SECs






|

.. code-block:: Python


    import matplotlib.pyplot as plt
    import numpy as np

    from pysecs import SECS, T_df, make_grid


    R_E = 6378e3
    R_I = R_E + 110e3
    rng = np.random.default_rng(7)

    # An irregular ground station network, as one would get from a real
    # observatory list rather than a hand-picked regular layout
    nobs = 14
    obs_lat = rng.uniform(45, 65, nobs)
    obs_lon = rng.uniform(-15, 25, nobs)
    obs_loc = np.column_stack([obs_lat, obs_lon, np.full(nobs, R_E)])

    # A synthetic "true" current system on a fine grid, used to generate
    # synthetic station observations
    truth_grid = make_grid(obs_loc, R_I, spacing=1.0)
    truth_amps = (
        1e4
        * np.exp(-(((truth_grid[:, 0] - 57) / 6) ** 2))
        * np.cos(np.deg2rad(truth_grid[:, 1]) * 3)
    )
    B_obs = np.tensordot(truth_amps, T_df(obs_loc, truth_grid), (0, 2))

    # Automatically generate the fitting grid from the station locations
    # alone -- no manually chosen spacing, bounds, or pole positions
    secs = SECS.from_observations(obs_loc, r_shell=R_I)
    secs.fit(obs_loc, B_obs)
    print(f"auto-generated grid: {secs.nsec} SECs")

    # Predict the current density on a map for plotting
    plat, plon = np.meshgrid(
        np.linspace(42, 68, 60), np.linspace(-18, 28, 60), indexing="ij"
    )
    pred_loc = np.column_stack([plat.ravel(), plon.ravel(), np.full(plat.size, R_I)])
    J_pred = secs.predict_J(pred_loc)
    J_mag = np.linalg.norm(J_pred[:, :2], axis=-1).reshape(plat.shape)

    fig, ax = plt.subplots()
    pcm = ax.pcolormesh(plon, plat, J_mag * 1e3, shading="auto", cmap="viridis")
    ax.scatter(obs_lon, obs_lat, c="w", edgecolor="k", s=40, label="stations")
    ax.scatter(
        secs.sec_df_loc[:, 1], secs.sec_df_loc[:, 0], c="r", s=2, alpha=0.4, label="SECs"
    )
    ax.set_xlabel("longitude (deg)")
    ax.set_ylabel("latitude (deg)")
    ax.set_title("Auto-generated grid: fitted horizontal current density")
    ax.legend(loc="lower right")
    fig.colorbar(pcm, ax=ax, label=r"|J$_h$| (mA/m)")
    plt.show()


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.290 seconds)


.. _sphx_glr_download_examples_plot_auto_grid.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_auto_grid.ipynb <plot_auto_grid.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_auto_grid.py <plot_auto_grid.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_auto_grid.zip <plot_auto_grid.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_