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Epoch fix (#5) 

Correct modified julian
feature/19
Daniel Warner 2018-08-25 12:50:39 +01:00 committed by GitHub
parent a38a8fdbba
commit c48d723692
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4 changed files with 12 additions and 11 deletions
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10
libsgp4/DateTime.h
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@ -618,6 +618,16 @@ public:
return Util::WrapTwoPI(Util::DegreesToRadians(theta / 240.0)); return Util::WrapTwoPI(Util::DegreesToRadians(theta / 240.0));
} }
/**
* Return the modified julian date since the j2000 epoch
* January 1, 2000, at 12:00 TT
* @returns the modified julian date
*/
double ToJ2000() const
{
return ToJulian() - 2415020.0;
}
/** /**
* Convert to local mean sidereal time (GMST plus the observer's longitude) * Convert to local mean sidereal time (GMST plus the observer's longitude)
* @param[in] lon observers longitude * @param[in] lon observers longitude

9
libsgp4/Globals.h
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@ -70,14 +70,5 @@ const double kSECONDS_PER_DAY = 86400.0;
const double kMINUTES_PER_DAY = 1440.0; const double kMINUTES_PER_DAY = 1440.0;
const double kHOURS_PER_DAY = 24.0; const double kHOURS_PER_DAY = 24.0;
// Jan 1.0 1900 = Jan 1 1900 00h UTC
const double kEPOCH_JAN1_00H_1900 = 2415019.5;
// Jan 1.5 1900 = Jan 1 1900 12h UTC
const double kEPOCH_JAN1_12H_1900 = 2415020.0;
// Jan 1.5 2000 = Jan 1 2000 12h UTC
const double kEPOCH_JAN1_12H_2000 = 2451545.0;
#endif #endif

2
libsgp4/SGP4.cpp
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@ -672,7 +672,7 @@ void SGP4::DeepSpaceInitialise(
/* /*
* initialize lunar / solar terms * initialize lunar / solar terms
*/ */
const double jday = elements_.Epoch().ToJulian() - kEPOCH_JAN1_12H_2000; const double jday = elements_.Epoch().ToJ2000();
const double xnodce = 4.5236020 - 9.2422029e-4 * jday; const double xnodce = 4.5236020 - 9.2422029e-4 * jday;
const double xnodce_temp = fmod(xnodce, kTWOPI); const double xnodce_temp = fmod(xnodce, kTWOPI);

2
libsgp4/SolarPosition.cpp
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@ -24,7 +24,7 @@
Eci SolarPosition::FindPosition(const DateTime& dt) Eci SolarPosition::FindPosition(const DateTime& dt)
{ {
const double mjd = dt.ToJulian() - kEPOCH_JAN1_12H_1900; const double mjd = dt.ToJ2000();
const double year = 1900 + mjd / 365.25; const double year = 1900 + mjd / 365.25;
const double T = (mjd + Delta_ET(year) / kSECONDS_PER_DAY) / 36525.0; const double T = (mjd + Delta_ET(year) / kSECONDS_PER_DAY) / 36525.0;
const double M = Util::DegreesToRadians(Util::Wrap360(358.47583 const double M = Util::DegreesToRadians(Util::Wrap360(358.47583