83 lines
2.2 KiB
C++
83 lines
2.2 KiB
C++
#include "Eci.h"
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#include "Util.h"
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void Eci::ToEci(const Julian& date, const CoordGeodetic &g)
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{
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/*
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* set date
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*/
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date_ = date;
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static const double mfactor = kTWOPI * (kOMEGA_E / kSECONDS_PER_DAY);
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/*
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* Calculate Local Mean Sidereal Time for observers longitude
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*/
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const double theta = date_.ToLocalMeanSiderealTime(g.longitude);
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/*
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* take into account earth flattening
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*/
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const double c = 1.0
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/ sqrt(1.0 + kF * (kF - 2.0) * pow(sin(g.latitude), 2.0));
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const double s = pow(1.0 - kF, 2.0) * c;
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const double achcp = (kXKMPER * c + g.altitude) * cos(g.latitude);
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/*
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* X position in km
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* Y position in km
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* Z position in km
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* W magnitude in km
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*/
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position_.x = achcp * cos(theta);
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position_.y = achcp * sin(theta);
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position_.z = (kXKMPER * s + g.altitude) * sin(g.latitude);
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position_.w = position_.GetMagnitude();
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/*
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* X velocity in km/s
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* Y velocity in km/s
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* Z velocity in km/s
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* W magnitude in km/s
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*/
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velocity_.x = -mfactor * position_.y;
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velocity_.y = mfactor * position_.x;
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velocity_.z = 0.0;
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velocity_.w = velocity_.GetMagnitude();
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}
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CoordGeodetic Eci::ToGeodetic() const
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{
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const double theta = Util::AcTan(position_.y, position_.x);
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// 0 >= lon < 360
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// const double lon = Fmod2p(theta - date_.ToGreenwichSiderealTime());
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// 180 >= lon < 180
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const double lon = fmod(theta - date_.ToGreenwichSiderealTime(), kPI);
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const double r = sqrt((position_.x * position_.x)
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+ (position_.y * position_.y));
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static const double e2 = kF * (2.0 - kF);
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double lat = Util::AcTan(position_.z, r);
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double phi = 0.0;
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double c = 0.0;
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int cnt = 0;
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do
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{
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phi = lat;
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const double sinphi = sin(phi);
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c = 1.0 / sqrt(1.0 - e2 * sinphi * sinphi);
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lat = Util::AcTan(position_.z + kXKMPER * c * e2 * sinphi, r);
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cnt++;
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}
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while (fabs(lat - phi) >= 1e-10 && cnt < 10);
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const double alt = r / cos(lat) - kXKMPER * c;
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return CoordGeodetic(lat, lon, alt, true);
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}
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