public GCEquatorialCoords getTopocentricEquatorial(GCEarthData obs, double jdate)
{
double u, h, delta_alpha;
double rho_sin, rho_cos;
const double b_a = 0.99664719;
GCEquatorialCoords tec = new GCEquatorialCoords();
double altitude = 0;
// geocentric position of observer on the earth surface
// 10.1 - 10.3
u = GCMath.arcTanDeg(b_a * b_a * GCMath.tanDeg(obs.latitudeDeg));
rho_sin = b_a * GCMath.sinDeg(u) + altitude / 6378140.0 * GCMath.sinDeg(obs.latitudeDeg);
rho_cos = GCMath.cosDeg(u) + altitude / 6378140.0 * GCMath.cosDeg(obs.latitudeDeg);
// equatorial horizontal paralax
// 39.1
double parallax = GCMath.arcSinDeg(GCMath.sinDeg(8.794 / 3600) / (radius / GCMath.AU));
// geocentric hour angle of the body
h = GCEarthData.SiderealTimeGreenwich(jdate) + obs.longitudeDeg - rightAscension;
// 39.2
delta_alpha = GCMath.arcTanDeg(
(-rho_cos * GCMath.sinDeg(parallax) * GCMath.sinDeg(h)) /
(GCMath.cosDeg(this.declination) - rho_cos * GCMath.sinDeg(parallax) * GCMath.cosDeg(h)));
tec.rightAscension = rightAscension + delta_alpha;
tec.declination = declination + GCMath.arcTanDeg(
((GCMath.sinDeg(declination) - rho_sin * GCMath.sinDeg(parallax)) * GCMath.cosDeg(delta_alpha)) /
(GCMath.cosDeg(declination) - rho_cos * GCMath.sinDeg(parallax) * GCMath.cosDeg(h)));
return(tec);
}
public static GCHorizontalCoords equatorialToHorizontalCoords(GCEquatorialCoords eqc, GCEarthData obs, double date)
{
double localHourAngle;
GCHorizontalCoords hc;
localHourAngle = GCMath.putIn360(GCEarthData.SiderealTimeGreenwich(date) - eqc.rightAscension + obs.longitudeDeg);
hc.azimut = GCMath.rad2deg(Math.Atan2(GCMath.sinDeg(localHourAngle),
GCMath.cosDeg(localHourAngle) * GCMath.sinDeg(obs.latitudeDeg) -
GCMath.tanDeg(eqc.declination) * GCMath.cosDeg(obs.latitudeDeg)));
hc.elevation = GCMath.rad2deg(Math.Asin(GCMath.sinDeg(obs.latitudeDeg) * GCMath.sinDeg(eqc.declination) +
GCMath.cosDeg(obs.latitudeDeg) * GCMath.cosDeg(eqc.declination) * GCMath.cosDeg(localHourAngle)));
return(hc);
}
