Orbit.h

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// Copyright © 2008-2024 Pioneer Developers. See AUTHORS.txt for details
// Licensed under the terms of the GPL v3. See licenses/GPL-3.txt
 
#ifndef ORBIT_H
#define ORBIT_H
 
#include "matrix3x3.h"
#include "vector3.h"
 
#include <cassert>
#include <cmath>
 
class Orbit {
public:
    // utility functions for simple calculations
    static double OrbitalPeriod(double semiMajorAxis, double centralMass);
    static double OrbitalPeriodTwoBody(double semiMajorAxis, double totalMass, double bodyMass);
 
    // note: the resulting Orbit is at the given position at t=0
    static Orbit FromBodyState(const vector3d &position, const vector3d &velocity, double central_mass);
    static Orbit ForStaticBody(const vector3d &position);
 
    Orbit() :
        m_eccentricity(0.0),
        m_semiMajorAxis(0.0),
        m_orbitalPhaseAtStart(0.0),
        m_velocityAreaPerSecond(0.0),
        m_orient(matrix3x3d::Identity())
    {}
 
    void SetShapeAroundBarycentre(double semiMajorAxis, double totalMass, double bodyMass, double eccentricity);
    void SetShapeAroundPrimary(double semiMajorAxis, double totalMass, double eccentricity);
    void SetPlane(const matrix3x3d &orient)
    {
        m_orient = orient;
        assert(!std::isnan(m_orient[0]) && !std::isnan(m_orient[1]) && !std::isnan(m_orient[2]));
        assert(!std::isnan(m_orient[3]) && !std::isnan(m_orient[4]) && !std::isnan(m_orient[5]));
        assert(!std::isnan(m_orient[6]) && !std::isnan(m_orient[7]) && !std::isnan(m_orient[8]));
    }
    void SetPhase(double orbitalPhaseAtStart) { m_orbitalPhaseAtStart = orbitalPhaseAtStart; }
 
    vector3d OrbitalPosAtTime(double t) const;
    double OrbitalTimeAtPos(const vector3d &pos, double centralMass) const;
    vector3d OrbitalVelocityAtTime(double totalMass, double t) const;
 
    // 0.0 <= t <= 1.0. Not for finding orbital pos
    vector3d EvenSpacedPosTrajectory(double t, double timeOffset = 0) const;
 
    double Period() const;
    vector3d Apogeum() const;
    vector3d Perigeum() const;
 
    // basic accessors
    double GetEccentricity() const { return m_eccentricity; }
    double GetSemiMajorAxis() const { return m_semiMajorAxis; }
    double GetOrbitalPhaseAtStart() const { return m_orbitalPhaseAtStart; }
    const matrix3x3d &GetPlane() const { return m_orient; }
 
private:
    double TrueAnomalyFromMeanAnomaly(double MeanAnomaly) const;
    double MeanAnomalyFromTrueAnomaly(double trueAnomaly) const;
    double MeanAnomalyAtTime(double time) const;
 
    vector3d m_positionForStaticBody;
    double m_eccentricity;
    double m_semiMajorAxis;
    double m_orbitalPhaseAtStart; // 0 to 2 pi radians
    /* dup " " --------------------------------------- */
    double m_velocityAreaPerSecond; // seconds
    matrix3x3d m_orient;
};
 
#endif