// ///////////////////////////////////////////////////////////////////
// Calculate the ECI coordinates of the location "geo" at time "date".
// Assumes geo coordinates are km-based.
// Assumes the earth is an oblate spheroid as defined in WGS '72.
// Reference: The 1992 Astronomical Almanac, page K11
// Reference: www.celestrak.com (Dr. TS Kelso)
public Eci(CoordGeo geo, Julian date)
{
m_VectorUnits = VectorUnits.Km;
double mfactor = Globals.TWOPI * (Globals.OMEGA_E / Globals.SEC_PER_DAY);
double lat = geo.Latitude;
double lon = geo.Longitude;
double alt = geo.Altitude;
// Calculate Local Mean Sidereal Time (theta)
double theta = date.toLMST(lon);
double c = 1.0 / Math.Sqrt(1.0 + Globals.F * (Globals.F - 2.0) * Globals.Sqr(Math.Sin(lat)));
double s = Globals.Sqr(1.0 - Globals.F) * c;
double achcp = (Globals.XKMPER * c + alt) * Math.Cos(lat);
m_Date = date;
m_Position = new Vector();
m_Position.X = achcp * Math.Cos(theta); // km
m_Position.Y = achcp * Math.Sin(theta); // km
m_Position.Z = (Globals.XKMPER * s + alt) * Math.Sin(lat); // km
m_Position.W = Math.Sqrt(Globals.Sqr(m_Position.X) +
Globals.Sqr(m_Position.Y) +
Globals.Sqr(m_Position.Z)); // range, km
m_Velocity = new Vector();
m_Velocity.X = -mfactor * m_Position.Y; // km / sec
m_Velocity.Y = mfactor * m_Position.X;
m_Velocity.Z = 0.0;
m_Velocity.W = Math.Sqrt(Globals.Sqr(m_Velocity.X) + // range rate km/sec^2
Globals.Sqr(m_Velocity.Y));
}
private CoordGeo m_geo; // lat, lon, alt of earth site
#region Construction
// //////////////////////////////////////////////////////////////////////////
public Site(CoordGeo geo)
{
m_geo = geo;
}
// ///////////////////////////////////////////////////////////////////////////
// c'tor accepting:
// Latitude in degress (negative south)
// Longitude in degress (negative west)
// Altitude in km
public Site(double degLat, double degLon, double kmAlt)
{
m_geo =
new CoordGeo(Globals.Deg2Rad(degLat), Globals.Deg2Rad(degLon), kmAlt);
}
public CoordGeo ToGeo()
{
double num;
double num1;
//this.Ae2Km();
double num2 = Globals.AcTan(Position.Y, Position.X);
double gmst = (num2 - jDate.ToGmst()) % 6.28318530717959;
if (gmst < 0)
{
gmst = gmst + 6.28318530717959;
}
double num3 = Math.Sqrt(Globals.Sqr(Position.X) + Globals.Sqr(Position.Y));
double num4 = 0.00669431777826672;
double num5 = Globals.AcTan(Position.Z, num3);
do
{
num = num5;
num1 = 1 / Math.Sqrt(1 - num4 * Globals.Sqr(Math.Sin(num)));
num5 = Globals.AcTan(Position.Z + 6378.135 * num1 * num4 * Math.Sin(num), num3);
}
while (Math.Abs(num5 - num) > 1E-07);
double num6 = num3 / Math.Cos(num5) - 6378.135 * num1;
CoordGeo coordGeo = new CoordGeo(num5, gmst, num6);
return coordGeo;
}
