04_all_center_conversions.cpp

Standard center shifts, identity shifts, and bodycentric conversions.

// SPDX-License-Identifier: AGPL-3.0-or-later
// Copyright (C) 2026 Vallés Puig, Ramon
 
 
#include <siderust/siderust.hpp>
 
#include <iomanip>
#include <iostream>
 
using namespace siderust;
using namespace siderust::frames;
using namespace siderust::centers;
using namespace qtty::literals;
 
using F = EclipticMeanJ2000;
using U = qtty::AstronomicalUnit;
 
// ─── Standard center shifts ──────────────────────────────────────────────────
 
template <typename C1, typename C2>
void show_center_conversion(const Time<TT, JD> &jd, const cartesian::Position<C1, F, U> &src) {
  auto out = src.template to_center<C2>(jd);
  auto back = out.template to_center<C1>(jd);
  auto err = (src - back).magnitude();
 
  std::cout << std::left << std::setw(12) << CenterTraits<C1>::name() << " -> " << std::setw(12)
            << CenterTraits<C2>::name() << " out=(" << std::showpos << std::fixed
            << std::setprecision(9) << out << std::noshowpos << ")  roundtrip=" << std::scientific
            << std::setprecision(3) << err << std::fixed << std::endl;
}
 
// ─── Bodycentric ─────────────────────────────────────────────────────────────
 
template <typename C>
void show_bodycentric_conversion(const char *label, const Time<TT, JD> &jd,
                                 const cartesian::Position<C, F, U> &src,
                                 const BodycentricParams &params) {
  auto bary = to_bodycentric(src, params, jd);
  auto recovered_geo = bary.to_geocentric(jd);
  auto recovered = recovered_geo.template to_center<C>(jd);
  auto err = (src - recovered).magnitude();
 
  std::cout << std::left << std::setw(12) << label << " -> " << std::setw(12) << "Bodycentric";
  std::cout << " dist=" << std::fixed << std::setprecision(6) << bary.distance();
  std::cout << "  roundtrip=" << std::scientific << std::setprecision(3) << err << std::fixed
            << std::endl;
}
 
// ─── main
// ─────────────────────────────────────────────────────────────────────
 
int main() {
  Time<TT, JD> jd(2460000.5);
  std::cout << "Center conversion demo at JD(TT) = " << std::fixed << std::setprecision(1) << jd
            << "\n"
            << std::endl;
 
  cartesian::Position<Barycentric, F, U> p_bary(0.40, -0.10, 1.20);
  auto p_helio = p_bary.to_center<Heliocentric>(jd);
  auto p_geo = p_bary.to_center<Geocentric>(jd);
 
  // ── Standard center shifts ────────────────────────────────────────────────
  std::cout << "── Standard center shifts "
               "─────────────────────────────────────────────\n";
 
  // Barycentric source
  show_center_conversion<Barycentric, Barycentric>(jd, p_bary);
  show_center_conversion<Barycentric, Heliocentric>(jd, p_bary);
  show_center_conversion<Barycentric, Geocentric>(jd, p_bary);
 
  // Heliocentric source
  show_center_conversion<Heliocentric, Heliocentric>(jd, p_helio);
  show_center_conversion<Heliocentric, Barycentric>(jd, p_helio);
  show_center_conversion<Heliocentric, Geocentric>(jd, p_helio);
 
  // Geocentric source
  show_center_conversion<Geocentric, Geocentric>(jd, p_geo);
  show_center_conversion<Geocentric, Barycentric>(jd, p_geo);
  show_center_conversion<Geocentric, Heliocentric>(jd, p_geo);
 
  // ── Bodycentric: Mars-like orbit (heliocentric reference) ──────────────────
  std::cout << "\n── Bodycentric – Mars-like orbit (heliocentric ref) "
               "───────────────────\n";
  KeplerianOrbit mars_orbit{1.524_au,             // semi_major_axis
                            Eccentricity{0.0934}, // eccentricity
                            1.85_deg,             // inclination
                            49.56_deg,            // lon_ascending_node
                            286.5_deg,            // arg_periapsis
                            19.41_deg,            // mean_anomaly
                            jd};
  auto mars_params = BodycentricParams::heliocentric(mars_orbit);
 
  show_bodycentric_conversion("Heliocentric", jd, p_helio, mars_params);
  show_bodycentric_conversion("Barycentric", jd, p_bary, mars_params);
  show_bodycentric_conversion("Geocentric", jd, p_geo, mars_params);
 
  // ── Bodycentric: ISS-like orbit (geocentric reference) ────────────────────
  std::cout << "\n── Bodycentric – ISS-like orbit (geocentric ref) "
               "──────────────────────\n";
  KeplerianOrbit iss_orbit{0.0000426_au,        // ~6 378 km in AU
                           Eccentricity{0.001}, // eccentricity
                           51.6_deg,            // inclination
                           0.0_deg,             // lon_ascending_node
                           0.0_deg,             // arg_periapsis
                           0.0_deg,             // mean_anomaly
                           jd};
  auto iss_params = BodycentricParams::geocentric(iss_orbit);
 
  show_bodycentric_conversion("Heliocentric", jd, p_helio, iss_params);
  show_bodycentric_conversion("Barycentric", jd, p_bary, iss_params);
  show_bodycentric_conversion("Geocentric", jd, p_geo, iss_params);
 
  // ── Topocentric ───────────────────────────────────────────────────────────
  // NOTE: Topocentric position transforms are not yet available in the C FFI;
  // Topocentric phase/altitude/azimuth queries are available via the altitude
  // and lunar_phase modules.  This section will be enabled once
  // siderust_to_topocentric / siderust_from_topocentric FFI functions are
  // added.
 
  return 0;
}