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/*
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* Copyright (C) 2020 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "game/systems/astronomy-system.hpp"
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#include "game/astronomy/celestial-coordinates.hpp"
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#include "game/astronomy/celestial-mechanics.hpp"
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#include "game/astronomy/celestial-time.hpp"
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#include "game/astronomy/astronomical-constants.hpp"
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#include "game/components/orbit-component.hpp"
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#include "game/components/transform-component.hpp"
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using namespace ecs;
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static constexpr double seconds_per_day = 24.0 * 60.0 * 60.0;
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astronomy_system::astronomy_system(entt::registry& registry):
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entity_system(registry),
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universal_time(0.0),
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days_per_timestep(1.0 / seconds_per_day),
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observer_location{0.0, 0.0, 0.0},
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lst(0.0),
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obliquity(0.0),
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ke_tolerance(1e-6),
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ke_iterations(10)
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{}
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void astronomy_system::update(double t, double dt)
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{
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const double dt_days = dt * days_per_timestep;
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// Add scaled timestep to current time
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set_universal_time(universal_time + dt_days);
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// Update horizontal (topocentric) positions of orbiting bodies
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registry.view<orbit_component, transform_component>().each(
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[&](auto entity, auto& orbit, auto& transform)
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{
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ast::orbital_elements orbital_elements;
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orbital_elements.a = orbit.a + orbit.d_a * universal_time;
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orbital_elements.ec = orbit.ec + orbit.d_ec * universal_time;
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orbital_elements.w = orbit.w + orbit.d_w * universal_time;
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orbital_elements.ma = math::wrap_radians(orbit.ma + orbit.d_ma * universal_time);
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orbital_elements.i = orbit.i + orbit.d_i * universal_time;
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orbital_elements.om = math::wrap_radians(orbit.om + orbit.d_om * universal_time);
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// Calculate ecliptic orbital position
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double3 ecliptic = ast::orbital_elements_to_ecliptic(orbital_elements, ke_tolerance, ke_iterations);
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// Transform orbital position from ecliptic space to horizontal space
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double3 horizontal = ecliptic_to_horizontal * ecliptic;
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// Subtract observer's radial distance (planet radius + observer's altitude)
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horizontal.z -= observer_location[0];
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// Calculate azimuth and elevation
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double3 spherical = ast::rectangular_to_spherical(horizontal);
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double2 az_el = {spherical.z - math::pi<double>, spherical.y};
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// Transform into local right-handed coordinates
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double3 translation = ast::horizontal_to_right_handed * horizontal;
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double3x3 rotation = ast::horizontal_to_right_handed * ecliptic_to_horizontal;
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transform.local.translation = math::type_cast<float>(translation);
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transform.local.rotation = math::type_cast<float>(math::quaternion_cast(rotation));
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});
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}
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void astronomy_system::set_universal_time(double time)
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{
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universal_time = time;
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update_axial_rotation();
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}
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void astronomy_system::set_time_scale(double scale)
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{
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days_per_timestep = scale / seconds_per_day;
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}
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void astronomy_system::set_observer_location(const double3& location)
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{
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observer_location = location;
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update_sidereal_time();
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}
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void astronomy_system::set_obliquity(double angle)
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{
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obliquity = angle;
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update_ecliptic_to_horizontal();
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}
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void astronomy_system::set_axial_rotation_speed(double speed)
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{
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axial_rotation_speed = speed;
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}
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void astronomy_system::set_axial_rotation_at_epoch(double angle)
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{
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axial_rotation_at_epoch = angle;
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update_axial_rotation();
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}
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void astronomy_system::update_axial_rotation()
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{
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axial_rotation = math::wrap_radians<double>(axial_rotation_at_epoch + universal_time * axial_rotation_speed);
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update_sidereal_time();
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}
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void astronomy_system::update_sidereal_time()
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{
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lst = math::wrap_radians<double>(axial_rotation + observer_location[2]);
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update_ecliptic_to_horizontal();
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}
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void astronomy_system::update_ecliptic_to_horizontal()
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{
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ecliptic_to_horizontal = ast::ecliptic_to_horizontal(obliquity, observer_location[1], lst);
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}
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