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Fix epoch naming #38

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Fix epoch naming #38

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12 changes: 11 additions & 1 deletion libsgp4/DateTime.h
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Original file line number Diff line number Diff line change
Expand Up @@ -626,14 +626,24 @@ class DateTime
return Util::WrapTwoPI(Util::DegreesToRadians(gt / 240.0));
}

/**
* Return the modified julian date since the j1900 epoch
* January 1, 1900, at 12:00 TT
* @returns the modified julian date
*/
double ToJ1900() const
{
return ToJulian() - 2415020.0;
}

/**
* 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;
return ToJulian() - 2451545.0;
}

/**
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2 changes: 1 addition & 1 deletion libsgp4/SGP4.cc
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Expand Up @@ -721,7 +721,7 @@ void SGP4::DeepSpaceInitialise(
/*
* initialize lunar / solar terms
*/
const double jday = elements_.Epoch().ToJ2000();
const double jday = elements_.Epoch().ToJ1900();

const double xnodce = Util::WrapTwoPI(4.5236020 - 9.2422029e-4 * jday);
const double stem = sin(xnodce);
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2 changes: 1 addition & 1 deletion libsgp4/SolarPosition.cc
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Expand Up @@ -27,7 +27,7 @@ namespace libsgp4

Eci SolarPosition::FindPosition(const DateTime& dt)
{
const double mjd = dt.ToJ2000();
const double mjd = dt.ToJ1900();
const double year = 1900 + mjd / 365.25;
const double T = (mjd + Delta_ET(year) / kSECONDS_PER_DAY) / 36525.0;
const double M = Util::DegreesToRadians(Util::Wrap360(358.47583
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