source/src/physics/orbit/frame.hpp

/*
 * Copyright (C) 2021  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef ANTKEEPER_PHYSICS_ORBIT_FRAME_HPP
#define ANTKEEPER_PHYSICS_ORBIT_FRAME_HPP

#include "math/se3.hpp"
#include <cmath>

namespace physics {
namespace orbit {

/// Orbital reference frames.
namespace frame {

/// Perifocal (PQW) frame.
namespace pqw {
	
	/**
	 * Converts PQW coordinates from Cartesian to spherical.
	 *
	 * @param v PQW Cartesian coordinates.
	 * @return PQW spherical coordinates, in the ISO order of radial distance, inclination (radians), and true anomaly (radians).
	 */
	template <class T>
	math::vector3<T> spherical(const math::vector3<T>& v)
	{
		const T xx_yy = v.x * v.x + v.y * v.y;
		
		return math::vector3<T>
		{
			std::sqrt(xx_yy + v.z * v.z),
			std::atan2(v.z, std::sqrt(xx_yy)),
			std::atan2(v.y, v.x)
		};
	}
	
	/**
	 * Constructs spherical PQW coordinates from Keplerian orbital elements.
	 *
	 * @param ec Eccentricity (e).
	 * @param a Semimajor axis (a).
	 * @param ea Eccentric anomaly (E), in radians.
	 * @param b Semiminor axis (b).
	 * @return PQW spherical coordinates, in the ISO order of radial distance, inclination (radians), and true anomaly (radians).
	 */
	template <class T>
	math::vector3<T> spherical(T ec, T a, T ea, T b)
	{
		const T x = a * (std::cos(ea) - ec);
		const T y = b * std::sin(ea);
		const T d = std::sqrt(x * x + y * y);
		const T ta = std::atan2(y, x);
		
		return math::vector3<T>{d, T(0), ta};
	}
	
	/**
	 * Constructs spherical PQW coordinates from Keplerian orbital elements.
	 *
	 * @param ec Eccentricity (e).
	 * @param a Semimajor axis (a).
	 * @param ea Eccentric anomaly (E), in radians.
	 * @return PQW spherical coordinates, in the ISO order of radial distance, inclination (radians), and true anomaly (radians).
	 */
	template <class T>
	math::vector3<T> spherical(T ec, T a, T ea)
	{
		const T b = a * std::sqrt(T(1) - ec * ec);
		return spherical<T>(ec, a, ea, b);
	}
	
	/**
	 * Converts PQW coordinates from spherical to Cartesian.
	 *
	 * @param PQW spherical coordinates, in the ISO order of radial distance, inclination (radians), and true anomaly (radians).
	 * @return PQW Cartesian coordinates.
	 */
	template <class T>
	math::vector3<T> cartesian(const math::vector3<T>& v)
	{
		const T x = v[0] * std::cos(v[1]);
		
		return math::vector3<T>
		{
			x * std::cos(v[2]),
			x * std::sin(v[2]),
			v[0] * std::sin(v[1]),
		};
	}
	
	/**
	 * Constructs Cartesian PQW coordinates from Keplerian orbital elements.
	 *
	 * @param ec Eccentricity (e).
	 * @param a Semimajor axis (a).
	 * @param ea Eccentric anomaly (E), in radians.
	 * @param b Semiminor axis (b).
	 * @return PQW Cartesian coordinates.
	 */
	template <class T>
	math::vector3<T> cartesian(T ec, T a, T ea, T b)
	{
		return cartesian<T>(spherical<T>(ec, a, ea, b));
	}
	
	/**
	 * Constructs Cartesian PQW coordinates from Keplerian orbital elements.
	 *
	 * @param ec Eccentricity (e).
	 * @param a Semimajor axis (a).
	 * @param ea Eccentric anomaly (E), in radians.
	 * @return PQW Cartesian coordinates.
	 */
	template <class T>
	math::vector3<T> cartesian(T ec, T a, T ea)
	{
		return cartesian<T>(spherical<T>(ec, a, ea));
	}

	/**
	 * Constructs an SE(3) transformation from a PQW frame to a BCI frame.
	 *
	 * @param om Right ascension of the ascending node (OMEGA), in radians.
	 * @param in Orbital inclination (i), in radians.
	 * @param w Argument of periapsis (omega), in radians.
	 * @return PQW to BCI transformation.
	 */
	template <typename T>
	math::transformation::se3<T> to_bci(T om, T in, T w)
	{
		const math::quaternion<T> r = math::normalize
		(
			math::quaternion<T>::rotate_z(om) *
				math::quaternion<T>::rotate_x(in) *
				math::quaternion<T>::rotate_z(w)
		);
		
		return math::transformation::se3<T>{{T(0), T(0), T(0)}, r};
	}

} // namespace pqw

/// Body-centered inertial (BCI) frame.
namespace bci {
	
	/**
	 * Converts BCI coordinates from spherical to Cartesian.
	 *
	 * @param v BCI spherical coordinates, in the ISO order of radial distance, declination (radians), and right ascension (radians).
	 * @return BCI Cartesian coordinates.
	 */
	template <class T>
	math::vector3<T> cartesian(const math::vector3<T>& v)
	{
		const T x = v[0] * std::cos(v[1]);
		
		return math::vector3<T>
		{
			x * std::cos(v[2]),
			x * std::sin(v[2]),
			v[0] * std::sin(v[1]),
		};
	}
	
	/**
	 * Converts BCI coordinates from Cartesian to spherical.
	 *
	 * @param v BCI Cartesian coordinates.
	 * @return BCI spherical coordinates, in the ISO order of radial distance, declination (radians), and right ascension (radians).
	 */
	template <class T>
	math::vector3<T> spherical(const math::vector3<T>& v)
	{
		const T xx_yy = v.x * v.x + v.y * v.y;
		
		return math::vector3<T>
		{
			std::sqrt(xx_yy + v.z * v.z),
			std::atan2(v.z, std::sqrt(xx_yy)),
			std::atan2(v.y, v.x)
		};
	}
	
	/**
	 * Constructs an SE(3) transformation from a BCI frame to a BCBF frame.
	 *
	 * @param ra Right ascension of the north pole, in radians.
	 * @param dec Declination of the north pole, in radians.
	 * @param w Location of the prime meridian, as a rotation about the north pole, in radians.
	 * @return BCI to BCBF transformation.
	 */
	template <typename T>
	math::transformation::se3<T> to_bcbf(T ra, T dec, T w)
	{
		const math::quaternion<T> r = math::normalize
		(
			math::quaternion<T>::rotate_z(-math::half_pi<T> - ra) *
				math::quaternion<T>::rotate_x(-math::half_pi<T> + dec) *
				math::quaternion<T>::rotate_z(-w)
		);
		
		return math::transformation::se3<T>{{T(0), T(0), T(0)}, r};
	}
	
	/**
	 * Constructs an SE(3) transformation from a BCI frame to a PQW frame.
	 *
	 * @param om Right ascension of the ascending node (OMEGA), in radians.
	 * @param in Orbital inclination (i), in radians.
	 * @param w Argument of periapsis (omega), in radians.
	 * @return BCI to PQW transformation.
	 */
	template <typename T>
	math::transformation::se3<T> to_pqw(T om, T in, T w)
	{
		const math::quaternion<T> r = math::normalize
		(
			math::quaternion<T>::rotate_z(-w) *
				math::quaternion<T>::rotate_x(-in) *
				math::quaternion<T>::rotate_z(-om)
		);
		
		return math::transformation::se3<T>{{T(0), T(0), T(0)}, r};
	}
	
} // namespace bci

/// Body-centered, body-fixed (BCBF) frame.
namespace bcbf {
	
	/**
	 * Converts BCBF coordinates from spherical to Cartesian.
	 *
	 * @param v BCBF spherical coordinates, in the ISO order of radial distance, latitude (radians), and longitude (radians).
	 * @return BCBF Cartesian coordinates.
	 */
	template <class T>
	math::vector3<T> cartesian(const math::vector3<T>& v)
	{
		const T x = v[0] * std::cos(v[1]);
		
		return math::vector3<T>
		{
			x * std::cos(v[2]),
			x * std::sin(v[2]),
			v[0] * std::sin(v[1]),
		};
	}
	
	/**
	 * Converts BCBF coordinates from Cartesian to spherical.
	 *
	 * @param v BCBF Cartesian coordinates.
	 * @return BCBF spherical coordinates, in the ISO order of radial distance, latitude (radians), and longitude (radians).
	 */
	template <class T>
	math::vector3<T> spherical(const math::vector3<T>& v)
	{
		const T xx_yy = v.x * v.x + v.y * v.y;
		
		return math::vector3<T>
		{
			std::sqrt(xx_yy + v.z * v.z),
			std::atan2(v.z, std::sqrt(xx_yy)),
			std::atan2(v.y, v.x)
		};
	}
	
	/**
	 * Constructs an SE(3) transformation from a BCBF frame to a BCI frame.
	 *
	 * @param ra Right ascension of the north pole, in radians.
	 * @param dec Declination of the north pole, in radians.
	 * @param w Location of the prime meridian, as a rotation about the north pole, in radians.
	 * @return BCBF to BCI transformation.
	 */
	template <typename T>
	math::transformation::se3<T> to_bci(T ra, T dec, T w)
	{
		const math::quaternion<T> r = math::normalize
		(
			math::quaternion<T>::rotate_z(w) *
				math::quaternion<T>::rotate_x(math::half_pi<T> - dec) *
				math::quaternion<T>::rotate_z(math::half_pi<T> + ra)

		);
		
		return math::transformation::se3<T>{{T(0), T(0), T(0)}, r};
	}
	
	/**
	 * Constructs an SE(3) transformation from a BCBF frame to an ENU frame.
	 *
	 * @param distance Radial distance of the observer from the center of the body.
	 * @param latitude Latitude of the observer, in radians.
	 * @param longitude Longitude of the observer, in radians.
	 * @return BCBF to ENU transformation.
	 */
	template <typename T>
	math::transformation::se3<T> to_enu(T distance, T latitude, T longitude)
	{
		const math::vector3<T> t = {T(0), T(0), -distance};
		const math::quaternion<T> r = math::normalize
		(
			math::quaternion<T>::rotate_x(-math::half_pi<T> + latitude) *
				math::quaternion<T>::rotate_z(-longitude - math::half_pi<T>)
		);
		
		return math::transformation::se3<T>{t, r};
	}

} // namespace bcbf

/// East, North, Up (ENU) horizontal frame.
namespace enu {
	
	/**
	 * Converts ENU coordinates from spherical to Cartesian.
	 *
	 * @param v ENU spherical coordinates, in the ISO order of radial distance, elevation (radians), and azimuth (radians).
	 * @return ENU Cartesian coordinates.
	 */
	template <class T>
	math::vector3<T> cartesian(const math::vector3<T>& v)
	{
		const T x = v[0] * std::cos(v[1]);
		const T y = math::half_pi<T> - v[2];
		
		return math::vector3<T>
		{
			x * std::cos(y),
			x * std::sin(y),
			v[0] * std::sin(v[1]),
		};
	}
	
	/**
	 * Converts ENU coordinates from Cartesian to spherical.
	 *
	 * @param v ENU Cartesian coordinates.
	 * @return ENU spherical coordinates, in the ISO order of radial distance, elevation (radians), and azimuth (radians).
	 */
	template <class T>
	math::vector3<T> spherical(const math::vector3<T>& v)
	{
		const T xx_yy = v.x * v.x + v.y * v.y;
		
		return math::vector3<T>
		{
			std::sqrt(xx_yy + v.z * v.z),
			std::atan2(v.z, std::sqrt(xx_yy)),
			math::half_pi<T> - std::atan2(v.y, v.x)
		};
	}
	
	/**
	 * Constructs an SE(3) transformation from an ENU frame to a BCBF frame.
	 *
	 * @param distance Radial distance of the observer from the center of the body.
	 * @param latitude Latitude of the observer, in radians.
	 * @param longitude Longitude of the observer, in radians.
	 * @return ENU to BCBF transformation.
	 */
	template <typename T>
	math::transformation::se3<T> to_bcbf(T distance, T latitude, T longitude)
	{
		const math::vector3<T> t = {T(0), T(0), distance};
		const math::quaternion<T> r = math::normalize
		(
			math::quaternion<T>::rotate_z(longitude + math::half_pi<T>) *
				math::quaternion<T>::rotate_x(math::half_pi<T> - latitude)
		);
		
		return math::transformation::se3<T>{r * t, r};
	}
	
} // namespace enu

} // namespace frame
} // namespace orbit
} // namespace physics

#endif // ANTKEEPER_PHYSICS_ORBIT_FRAME_HPP