/// <summary>
/// 由测站地心地固大地坐标计算在天球空间直角坐标的位置和速度。
/// </summary>
/// <param name="geo">大地坐标</param>
/// <param name="date">时间</param>
/// <param name="ellipsoid">参考椭球</param>
/// <param name="isKm">是否是千米</param>
/// <returns></returns>
public static MotionState GetMovingState(
GeoCoord geo,
Julian date,
Geo.Referencing.Ellipsoid ellipsoid = null,
bool isKm = true
)
{
double lat = geo.Lat;
double lon = geo.Lon;
double alt = geo.Altitude;
if (geo.Unit == AngleUnit.Degree)
{
lat = AngularConvert.DegToRad(lat);
lon = AngularConvert.DegToRad(lon);
}
if (ellipsoid == null)
{
ellipsoid = Geo.Referencing.Ellipsoid.WGS84;
}
double f = ellipsoid.Flattening;
double a = ellipsoid.SemiMajorAxis;
if (isKm)
{
a = ellipsoid.SemiMajorAxis / 1000.0;
}
// Calculate Local Mean Sidereal Time (theta)
double theta = date.GetLocalMeanSiderealTime(lon);
double c = 1.0 / Math.Sqrt(1.0 + f * (f - 2.0) * GeoMath.Sqr(Math.Sin(lat)));
double s = GeoMath.Sqr(1.0 - f) * c;
double achcp = (a * c + alt) * Math.Cos(lat);
XYZ pos = new XYZ();
pos.X = achcp * Math.Cos(theta);
pos.Y = achcp * Math.Sin(theta);
pos.Z = (a * s + alt) * Math.Sin(lat);
XYZ vel = GetVelocityInCelestialSphere(pos);
return(new MotionState(pos, vel));
}
/// <summary>
/// 根据卫星位置和测站位置计算其在站星坐标系中的位置。
/// Returns the topo-centric (azimuth, elevation, etc.) coordinates for
/// a target object described by the given ECI coordinates.
/// </summary>
/// <param name="satPos">The ECI coordinates of the target object.</param>
/// <param name="siteCoord">The ECI coordinates of the 观测站</param>
/// <returns>The look angle to the target object.</returns>
public static TopoCoord GetSatTopoCoord(TimedMotionState satPos, GeoCoord siteCoord)
{
// Calculate the ECI coordinates for this Site object at the time of interest.
Julian date = satPos.Date;
MotionState sitePos = OrbitUtils.GetMovingState(siteCoord, date);
XYZ vecV = satPos.Velocity - sitePos.Velocity;
XYZ vecP = satPos.Position - sitePos.Position;
// The site's Local Mean Sidereal Time at the time of interest.
double thetaRad = date.GetLocalMeanSiderealTime(siteCoord.Lon, false);
double sinLat = Math.Sin(siteCoord.Lat);
double cosLat = Math.Cos(siteCoord.Lat);
double sinTheta = Math.Sin(thetaRad);
double cosTheta = Math.Cos(thetaRad);
double top_s = sinLat * cosTheta * vecP.X +
sinLat * sinTheta * vecP.Y -
cosLat * vecP.Z;
double top_e = -sinTheta * vecP.X +
cosTheta * vecP.Y;
double top_z = cosLat * cosTheta * vecP.X +
cosLat * sinTheta * vecP.Y +
sinLat * vecP.Z;
double az = Math.Atan(-top_e / top_s);
if (top_s > 0.0)
{
az += OrbitConsts.PI;
}
if (az < 0.0)
{
az += 2.0 * OrbitConsts.PI;
}
double el = Math.Asin(top_z / vecP.Radius());
double rate = vecP.Dot(vecV) / vecP.Radius();
TopoCoord topo = new TopoCoord(
az, // azimuth, radians
el, // elevation, radians
vecP.Radius(), // range
rate // rate, per sec
);
#if WANT_ATMOSPHERIC_CORRECTION
// Elevation correction for atmospheric refraction.
// Reference: Astronomical Algorithms by Jean Meeus, pp. 101-104
// Note: Correction is meaningless when apparent elevation is below horizon
topo.Elevation += AngularConvert.DegToRad((1.02 /
Math.Tan(AngularConvert.DegToRad(AngularConvert.RadToDeg(el) + 10.3 /
(AngularConvert.RadToDeg(el) + 5.11)))) / 60.0);
if (topo.Elevation < 0.0)
{
topo.Elevation = el; // Reset to true elevation
}
if (topo.Elevation > (Consts.PI / 2.0))
{
topo.Elevation = (Consts.PI / 2.0);
}
#endif
return(topo);
}
