location.h

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#pragma once
 
#include "Math/TVector2.h"
#include "Math/constant.h"
#include "Math/time.h"
 
#include <cmath>
 
namespace ph::math
{
 
template<typename T>
inline TVector2<T> sun_sky_phi_theta(
    const T solarTime24H,
    const T julianDate,
    const T siteLatitudeRadians)
{
    using namespace ph::math::constant;
 
    // Approximated solar declination in radians
    const T delta = 
        static_cast<T>(0.4093) * std::sin(two_pi<T> * (julianDate - static_cast<T>(81)) / static_cast<T>(368));
 
    const T sinDelta    = std::sin(delta);
    const T cosDelta    = std::cos(delta);
    const T sinLatitude = std::sin(siteLatitudeRadians);
    const T cosLatitude = std::cos(siteLatitudeRadians);
 
    const T angleTerm    = pi<T> * solarTime24H / static_cast<T>(12);
    const T sinAngleTerm = std::sin(angleTerm);
    const T cosAngleTerm = std::cos(angleTerm);
 
    const T sunPhiPreetham = std::atan((-cosDelta * sinAngleTerm) / (cosLatitude * sinDelta - sinLatitude * cosDelta * cosAngleTerm));
    const T sunTheta       = pi<T> / static_cast<T>(2) - std::asin(sinLatitude * sinDelta - cosLatitude * cosDelta * cosAngleTerm);
 
    // Note that <sunPhiPreetham> here has (CW order)
    // 0 = south, pi/2 = west, pi = north and -pi/2 = east; 
    // convert it to engine order here.
    T sunPhi = -sunPhiPreetham + static_cast<T>(3 / 2) * pi<T>;
    sunPhi = sunPhi > two_pi<T> ? sunPhi - two_pi<T> : sunPhi;
 
    return {sunPhi, sunTheta};
}
 
}// end namespace ph::math