Temporal subsets of stratigraphy
--------------------------------

This example creates straigraphy for a temporal subset of the dataset.
This allows for a view of *time evolution of stratigraphy itself*, for example, the changing stack of an experiment through time.

In this example, we make the subsets into a movie, but the relevant lines for creating a subset are:

.. code::

    vol, elev = spl.strat.compute_boxy_stratigraphy_volume(
        aeolian_eta[:i],
        aeolian_time[:i],
        z=zs,
        sigma_dist=subsidence_rate,
    )

where the `:i` indicates the slice of all of the times to be used in the calculations. See :obj:`~sandplover.strat.compute_boxy_stratigraphy_volume`.

.. plot::
    :include-source:
    :context: reset
    :nofigs:

    import numpy as np
    import matplotlib.pyplot as plt
    from matplotlib import animation

    import sandplover as spl

    # set up to use constant z for stratigraphy, so all frames line up over time
    zs = np.arange(-10, 10, 0.25)

    # load the sample data and define indices to use in the plotting
    aeolian = spl.sample_data.aeolian()
    time_idxs = np.arange(100, 300, step=10)

    aeolian_eta = aeolian["eta"].copy()
    aeolian_time = aeolian["time"].copy()

    subsidence_rate = 0.01
    cross_section_idx = 10


    def update_field(i):
        vol, elev = spl.strat.compute_boxy_stratigraphy_volume(
            aeolian_eta[:i],
            aeolian_time[:i],
            z=zs,
            sigma_dist=subsidence_rate,
        )
        im.set_data(vol[:, :, cross_section_idx])


    # make one strat for the initial, to have the full shape of the image
    vol, elev = spl.strat.compute_boxy_stratigraphy_volume(
        aeolian_eta[: time_idxs[0]],
        aeolian_time[: time_idxs[0]],
        z=zs,
        sigma_dist=subsidence_rate,
    )

    # make the first frame
    fig, ax = plt.subplots(figsize=(6, 3))
    im = plt.imshow(
        vol[:, :, cross_section_idx],
        extent=[0, aeolian.dim1_coords[-1], elev.min(), elev.max()],
        aspect="auto",
        origin="lower",
        vmin=0,
        vmax=time_idxs[-1],
    )

Then, make the animation.


.. plot::
    :context:
    :nofigs:

    import os

    os.makedirs("../../../../build/plot_directive/guides/examples/plot/", exist_ok=True)

    anim = animation.FuncAnimation(fig, update_field, frames=time_idxs, interval=5)
    anim.save('../../../../build/plot_directive/guides/examples/plot/strat_movie.gif', fps=5)

    anim = animation.FuncAnimation(
        fig, update_field,
        frames=time_idxs,
        interval=5,
        blit=False)
    anim.save('../../../../build/plot_directive/guides/examples/plot/simple_movie.gif', fps=5)

    plt.show()


.. code::

    anim = animation.FuncAnimation(fig, update_field, frames=time_idxs, interval=5)
    anim.save("strat_movie.gif", fps=5)

    plt.show()


And view the gif:

.. image:: ../../../../build/plot_directive/guides/examples/plot/strat_movie.gif