Solar System Animation

In this tutorial, we will create an animation of the solar system using textured spheres. We will also show how to manipulate the position of these sphere actors in a timer_callback function to simulate orbital motion.

import itertools

import numpy as np

import fury

Create a scene to start.

scene = fury.window.Scene()

# Create a panel and the start/pause buttons

panel = fury.ui.Panel2D(size=(300, 100), color=(1, 1, 1), align="right")
panel.center = (400, 50)

pause_button = fury.ui.Button2D(
    icon_fnames=[("square", fury.data.read_viz_icons(fname="pause2.png"))]
)
start_button = fury.ui.Button2D(
    icon_fnames=[("square", fury.data.read_viz_icons(fname="play3.png"))]
)

# Add the buttons on the panel

panel.add_element(pause_button, (0.25, 0.33))
panel.add_element(start_button, (0.66, 0.33))

Define information relevant for each planet actor including its texture name, relative position, and scale.

planets_data = [
    {
        "filename": "8k_mercury.jpg",
        "position": 7,
        "earth_days": 58,
        "scale": (0.4, 0.4, 0.4),
    },
    {
        "filename": "8k_venus_surface.jpg",
        "position": 9,
        "earth_days": 243,
        "scale": (0.6, 0.6, 0.6),
    },
    {
        "filename": "1_earth_8k.jpg",
        "position": 11,
        "earth_days": 1,
        "scale": (0.4, 0.4, 0.4),
    },
    {
        "filename": "8k_mars.jpg",
        "position": 13,
        "earth_days": 1,
        "scale": (0.8, 0.8, 0.8),
    },
    {"filename": "jupiter.jpg", "position": 16, "earth_days": 0.41, "scale": (2, 2, 2)},
    {
        "filename": "8k_saturn.jpg",
        "position": 19,
        "earth_days": 0.45,
        "scale": (2, 2, 2),
    },
    {
        "filename": "8k_saturn_ring_alpha.png",
        "position": 19,
        "earth_days": 0.45,
        "scale": (3, 0.5, 3),
    },
    {
        "filename": "2k_uranus.jpg",
        "position": 22,
        "earth_days": 0.70,
        "scale": (1, 1, 1),
    },
    {
        "filename": "2k_neptune.jpg",
        "position": 25,
        "earth_days": 0.70,
        "scale": (1, 1, 1),
    },
    {"filename": "8k_sun.jpg", "position": 0, "earth_days": 27, "scale": (5, 5, 5)},
]
fury.data.fetch_viz_textures()

To take advantage of the previously defined data structure we are going to create an auxiliary function that will load and apply the respective texture, set its respective properties (relative position and scale), and add the actor to a previously created scene.

def init_planet(planet_data):
    """Initialize a planet actor.

    Parameters
    ----------
    planet_data : dict
        The planet_data is a dictionary, and the keys are filename(texture),
        position and scale.

    Returns
    -------
    planet_actor: actor
        The corresponding sphere actor with texture applied.
    """
    planet_file = fury.data.read_viz_textures(planet_data["filename"])
    planet_image = fury.io.load_image(planet_file)
    planet_actor = fury.actor.texture_on_sphere(planet_image)
    planet_actor.SetPosition(planet_data["position"], 0, 0)
    if planet_data["filename"] != "8k_saturn_ring_alpha.png":
        fury.utils.rotate(planet_actor, rotation=(90, 1, 0, 0))
    planet_actor.SetScale(planet_data["scale"])
    scene.add(planet_actor)
    return planet_actor

Use the map function to create actors for each of the texture files in the planet_files list. Then, assign each actor to its corresponding actor in the list.

planet_actor_list = list(map(init_planet, planets_data))

mercury_actor = planet_actor_list[0]
venus_actor = planet_actor_list[1]
earth_actor = planet_actor_list[2]
mars_actor = planet_actor_list[3]
jupiter_actor = planet_actor_list[4]
saturn_actor = planet_actor_list[5]
saturn_rings_actor = planet_actor_list[6]
uranus_actor = planet_actor_list[7]
neptune_actor = planet_actor_list[8]
sun_actor = planet_actor_list[9]

Define the gravitational constant G, the orbital radii of each of the planets, and the central mass of the sun. The gravity and mass will be used to calculate the orbital position, so multiply these two together to create a new constant, which we will call miu.

g_exponent = np.float_power(10, -11)
g_constant = 6.673 * g_exponent

m_exponent = 1073741824  # np.power(10, 30)
m_constant = 1.989 * m_exponent

miu = m_constant * g_constant

Let’s define two functions that will help us calculate the position of each planet as it orbits around the sun: get_orbit_period and get_orbital_position, using the constant miu and the orbital radii of each planet.

def get_orbit_period(radius):
    return 2 * np.pi * np.sqrt(np.power(radius, 3) / miu)


def get_orbital_position(radius, time):
    orbit_period = get_orbit_period(radius)
    x = radius * np.cos((-2 * np.pi * time) / orbit_period)
    y = radius * np.sin((-2 * np.pi * time) / orbit_period)
    return x, y

Let’s define a function to rotate the planet actor axially, we’ll be defining axis of each planet and angle by which it should be rotated using rotate_axial funtction

def rotate_axial(actor, time, radius):
    axis = (0, radius, 0)
    angle = 50 / time
    fury.utils.rotate(actor, rotation=(angle, axis[0], axis[1], axis[2]))
    return angle

Let’s change the camera position to visualize the planets better.

scene.set_camera(position=(-20, 60, 100))

Next, create a ShowManager object. The ShowManager class is the interface between the scene, the window and the interactor.

showm = fury.window.ShowManager(
    scene=scene, size=(900, 768), reset_camera=False, order_transparent=True
)
scene.add(panel)

Next, let’s focus on creating the animation. We can determine the duration of animation with using the counter. Use itertools to avoid global variables.

counter = itertools.count()

Define one new function to use in timer_callback to update the planet positions update_planet_position.

def update_planet_position(r_planet, planet_actor, cnt):
    pos_planet = get_orbital_position(r_planet, cnt)
    planet_actor.SetPosition(pos_planet[0], 0, pos_planet[1])
    return pos_planet

calculate_path function is for calculating the path/orbit of every planet.

def calculate_path(r_planet, c):
    planet_track = [
        [get_orbital_position(r_planet, i)[0], 0, get_orbital_position(r_planet, i)[1]]
        for i in range(c)
    ]
    return planet_track

First we are making a list that will contain radius from planets_data. Here we are not taking the radius of orbit/path for sun and saturn ring. planet_actors will contain all the planet actors. r_times will contain time taken (in days) by the planets to rotate around itself.

r_planets = [
    p_data["position"]
    for p_data in planets_data
    if "sun" not in p_data["filename"]
    if "saturn_ring" not in p_data["filename"]
]

planet_actors = [
    mercury_actor,
    venus_actor,
    earth_actor,
    mars_actor,
    jupiter_actor,
    saturn_actor,
    uranus_actor,
    neptune_actor,
]


sun_data = {
    "actor": sun_actor,
    "position": planets_data[9]["position"],
    "earth_days": planets_data[9]["earth_days"],
}

r_times = [p_data["earth_days"] for p_data in planets_data]

Here we are calculating and updating the path/orbit before animation starts.

planet_tracks = [calculate_path(rplanet, rplanet * 85) for rplanet in r_planets]

This is for orbit visualization. We are using line actor for orbits. After creating an actor we add it to the scene.

orbit_actor = fury.actor.line(planet_tracks, colors=(1, 1, 1), linewidth=0.1)
scene.add(orbit_actor)

Define the timer_callback function, which controls what events happen at certain times, using the counter. Update the position of each planet actor using update_planet_position, assigning the x and y values of each planet’s position with the newly calculated ones.

def timer_callback(_obj, _event):
    cnt = next(counter)
    showm.render()

    # Rotating the sun actor
    rotate_axial(sun_actor, sun_data["earth_days"], 1)

    for r_planet, p_actor, r_time in zip(r_planets, planet_actors, r_times):
        # if the planet is saturn then we also need to update the position
        # of its rings.
        if p_actor == saturn_actor:
            pos_saturn = update_planet_position(19, saturn_actor, cnt)
            saturn_rings_actor.SetPosition(pos_saturn[0], 0, pos_saturn[1])
        else:
            update_planet_position(r_planet, p_actor, cnt)
        rotate_axial(p_actor, r_time, r_planet)

    if cnt == 2000:
        showm.exit()

We add a callback to each button to perform some action.

def start_animation(i_ren, _obj, _button):
    showm.add_timer_callback(True, 10, timer_callback)


def pause_animation(i_ren, _obj, _button):
    showm.destroy_timers()


start_button.on_left_mouse_button_clicked = start_animation
pause_button.on_left_mouse_button_clicked = pause_animation

Watch the planets orbit the sun in your new animation!

showm.add_timer_callback(True, 10, timer_callback)
showm.start()

fury.window.record(
    scene=showm.scene, size=(900, 768), out_path="viz_solar_system_animation.png"
)