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orbit_animation

Author
importostar
Published
2020/05/07
Updated
2020/06/20
Article Outline

Example Python program orbit_animation.py Python version 3.x or newer. To check the Python version use:

python --version

Modules

  • import matplotlib
  • import matplotlib.pyplot as plt
  • import matplotlib.widgets as mwidgets
  • from datetime import datetime, timedelta
  • import numpy as np
  • import astropy.units as u
  • import astropy.constants as const
  • from astropy.visualization import quantity_support
  • import matplotlib.gridspec as gridspec
  • import matplotlib.ticker as mticker
  • from matplotlib.animation import FFMpegWriter
  • import heliopy.spice as spice
  • import heliopy.data.spice as spicedata
  • import spiceypy

Classes

  • class Body:

Methods

  • def dist_elev_azimuth(x, y, z):
  • def parker_spiral_phi(phi_0):
  • def plot_timeseries(bodies, times, coords):
  • def setup_animation_axes(ax):
  • def run_animation(bodies, times, coords, fig, axs, ax, vlines, fname):
  • def date2ndays(d):
  • def ndays2date(n):
  • def update(dtime):
  • def animate(bodies, times, coords, fname):
  • def init(self, name, plot_tseries, color, stime=None):
  • def generate_trajectory(self, times, coords):
  • def generate_times(start, end, delta):

Code

Python example

import matplotlib
matplotlib.use('qt5agg')
import matplotlib.pyplot as plt
import matplotlib.widgets as mwidgets

from datetime import datetime, timedelta
import numpy as np
import astropy.units as u
import astropy.constants as const
from astropy.visualization import quantity_support
import matplotlib.gridspec as gridspec
import matplotlib.ticker as mticker
from matplotlib.animation import FFMpegWriter

import heliopy.spice as spice
import heliopy.data.spice as spicedata
import spiceypy


def dist_elev_azimuth(x, y, z):
    dist = np.sqrt(x**2 + y**2 + z**2)
    elev = np.rad2deg(np.arcsin(z / dist))
    az = np.rad2deg(np.arctan2(y, x))
    return dist, elev, az


omega_sun = 405 * u.km * u.rad / u.s / const.au
vsw = 500 * u.km / u.s
spiral_rs_au = np.linspace(0, 2, 100) * const.au
spiral_rs = (spiral_rs_au / const.au).value


def parker_spiral_phi(phi_0):
    return phi_0 + omega_sun * spiral_rs_au / vsw


def plot_timeseries(bodies, times, coords):
    quantity_support()

    gs = gridspec.GridSpec(7, 1)
    fig = plt.figure(figsize=(10, 10))
    ax1 = plt.subplot(gs[0, 0])
    ax2 = plt.subplot(gs[1, 0], sharex=ax1)
    ax3 = plt.subplot(gs[2, 0], sharex=ax1)
    ax_orbit = plt.subplot(gs[4:, 0])
    fig.subplots_adjust(hspace=0)
    axs = [ax1, ax2, ax3]
    for ax in axs[:-1]:
        ax.xaxis.set_visible(False)

    for body in bodies:
        traj = body.trajectory
        dist, elev, az = dist_elev_azimuth(traj.x, traj.y, traj.z)
        axs[0].plot(traj.times, traj.r, lw=1, color=body.color)
        axs[1].plot(traj.times, elev, lw=1, color=body.color)
        axs[2].scatter(traj.times, az, s=0.5, color=body.color)

    axs[0].set_ylim(0, 1.1)
    axs[0].set_ylabel('r (AU)')

    axs[1].set_ylabel('Elevation')
    axs[1].set_ylim(-16, 16)
    axs[1].axhline(0, color='k', lw=1, linestyle='--')

    axs[2].set_ylabel('Azimuth')
    for val in [-90, 0, 90]:
        axs[2].axhline(val, color='k', lw=1, linestyle='--')
    axs[2].set_ylim(-180, 180)
    axs[2].yaxis.set_major_locator(mticker.FixedLocator([-90, 0, 90]))

    vlines = []
    for a in axs:
        line = a.axvline(starttime, color='k', lw=1)
        vlines.append(line)
        a.set_xlim(times[0], times[-1])

    return fig, axs, ax_orbit, vlines


def setup_animation_axes(ax):
    ax.scatter(0, 0, s=70, color='#feb24c', edgecolors='k', label='Sun')
    ax.set_xlim(-1.1, 1.1)
    ax.set_ylim(-1.1, 1.1)
    ax.set_xlabel('x (AU)')
    ax.set_ylabel('y (AU)')
    ax.set_aspect('equal', adjustable='box')


def run_animation(bodies, times, coords, fig, axs, ax, vlines, fname):
    # Use this as a reference date
    base_date = datetime(1974, 1, 1)

    def date2ndays(d):
        # Return number of days since base_date
        return (d - base_date).total_seconds() / (60 * 60 * 24)

    def ndays2date(n):
        # Return date given number of days since base_date
        return base_date + timedelta(days=n)

    # Scatter initial positions
    scatter_kwargs = {'marker': 'o', 'ms': 10, 'mec': 'k', 'zorder': 1}
    circles = {}
    lines = {}
    spirals = []

    # List of all the artists
    artists = []

    # Create initial body artists
    for body in bodies:
        circle, = ax.plot([], [],
                          label=body.name,
                          color=body.color,
                          **scatter_kwargs)
        line, = ax.plot([], [], color=body.color, zorder=-1)
        circles[body] = circle
        lines[body] = line
        artists.append(circle)
        artists.append(line)

    # Create initial spiral artists
    spirals = []
    for phi_0 in np.linspace(0, 2 * np.pi, 5)[:-1] * u.rad:
        phi = parker_spiral_phi(phi_0)
        line, = ax.plot(spiral_rs * np.sin(phi),
                        spiral_rs * np.cos(phi),
                        color='black', lw=1, zorder=-2, alpha=0.5)
        spirals.append([line, phi_0])
        artists.append(line)

    ax.legend(loc='upper left', bbox_to_anchor=(1, 1))
    dt = times[1] - times[0]

    def update(dtime):
        print(dtime)
        for body in bodies:
            # Get index of datetime
            index = np.where(body.times == dtime)[0]
            if index.size == 0:
                continue
            elif index.size == 1:
                index = index[0]
            else:
                raise RuntimeError('Index bigger than 1')

            index_current = index
            if coords == 'IAU_SUN':
                rewind = 7
            else:
                rewind = 14
            index_rewind = index - int(timedelta(days=rewind) / dt)
            if index_rewind < 0:
                index_rewind = 0

            if index_current >= 0:
                x = body.trajectory.x.value
                y = body.trajectory.y.value
                xdata = x[index_current]
                ydata = y[index_current]
                lines[body].set_xdata(x[index_rewind:index_current + 1])
                lines[body].set_ydata(y[index_rewind:index_current + 1])
                circles[body].set_xdata(xdata)
                circles[body].set_ydata(ydata)

        if coords != 'IAU_SUN':
            delta_t = (dtime - times[0]).total_seconds() * u.s
            delta_phi_0 = omega_sun * delta_t
            for line, phi_0 in spirals:
                phi = parker_spiral_phi(phi_0 - delta_phi_0)
                line.set_xdata(spiral_rs * np.sin(phi))
                line.set_ydata(spiral_rs * np.cos(phi))

        # Set date title
        ax.set_title(dtime.strftime('%d-%m-%Y'))

        # Change vlines
        for line in vlines:
            line.set_xdata(dtime)

        return artists

    # frames = range(len(times))
    moviewriter = FFMpegWriter(fps=24)
    with moviewriter.saving(fig, fname, dpi=100):
        for t in times:
            update(t)
            moviewriter.grab_frame()


def animate(bodies, times, coords, fname):
    '''
    bodies : list of string
        List of bodies to add to animation.
    times : list of datetimes
        List of datetimes to generate positions for for each body.
    coords : str
        Coordinates
    '''
    tseries_kernels = [b for b in bodies if b.plot_tseries]
    fig, axs, ax_anim, vlines = plot_timeseries(tseries_kernels, times, coords)
    setup_animation_axes(ax_anim)
    run_animation(bodies, times, coords, fig, axs, ax_anim, vlines, fname)


class Body:
    def __init__(self, name, plot_tseries, color, stime=None):
        self.name = name
        self.plot_tseries = plot_tseries
        self.color = color
        self.stime = stime

    def generate_trajectory(self, times, coords):
        traj = spice.Trajectory(self.name)
        if self.stime is None:
            gen_times = np.array(times)
        else:
            gen_times = np.array(times)
            gen_times = gen_times[gen_times > self.stime]

        traj.generate_positions(gen_times, 'Sun', coords)
        traj.change_units(u.au)
        self.times = gen_times
        self.trajectory = traj


def generate_times(start, end, delta):
    times = []
    while start < end:
        times.append(start)
        start += delta
    return times


if __name__ == '__main__':
    psp_kernels = spicedata.get_kernel('psp_pred')
    spice.furnish(psp_kernels)

    orbiter_kernel = spicedata.get_kernel('solo_2020')
    spice.furnish(orbiter_kernel)

    stereo_kernel = spicedata.get_kernel('stereo_a_pred')
    spice.furnish(stereo_kernel)
    coords = 'ECLIPJ2000'

    starttime = datetime(2018, 8, 13)
    endtime = datetime(2021, 6, 1)
    delta = timedelta(hours=12)
    times = generate_times(starttime, endtime, delta)

    spiceypy.spiceypy.boddef('PSP', -96)
    spiceypy.spiceypy.boddef('STEREO-A', -234)
    bodies = [Body('Solar Orbiter', True, 'C3', stime=datetime(2020, 2, 10)),
              Body('PSP', True, 'C0'),
              Body('STEREO-A', False, 'C4'),
              Body('Earth', False, 'C2'),
              ]

    for body in bodies:
        body.generate_trajectory(times, coords)

    fname = f'Movies/website/{coords}.mp4'
    animate(bodies, times, coords, fname)
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