Exemple #1
0
      /// <summary>
      /// Returns the topo-centric (azimuth, elevation, etc.) coordinates for
      /// a target object described by the given ECI coordinates.
      /// </summary>
      /// <param name="eci">The ECI coordinates of the target object.</param>
      /// <returns>The look angle to the target object.</returns>
      public TopoTime GetLookAngle(EciTime eci)
      {
         // Calculate the ECI coordinates for this Site object at the time
         // of interest.
         Julian  date     = eci.Date;
         EciTime eciSite  = GetPosition(date);
         Vector vecRgRate = new Vector(eci.Velocity.X - eciSite.Velocity.X,
                                       eci.Velocity.Y - eciSite.Velocity.Y,
                                       eci.Velocity.Z - eciSite.Velocity.Z);

         double x = eci.Position.X - eciSite.Position.X;
         double y = eci.Position.Y - eciSite.Position.Y;
         double z = eci.Position.Z - eciSite.Position.Z;
         double w = Math.Sqrt(Globals.Sqr(x) + Globals.Sqr(y) + Globals.Sqr(z));

         Vector vecRange = new Vector(x, y, z, w);

         // The site's Local Mean Sidereal Time at the time of interest.
         double theta = date.ToLmst(LongitudeRad);

         double sin_lat   = Math.Sin(LatitudeRad);
         double cos_lat   = Math.Cos(LatitudeRad);
         double sin_theta = Math.Sin(theta);
         double cos_theta = Math.Cos(theta);

         double top_s = sin_lat * cos_theta * vecRange.X + 
                        sin_lat * sin_theta * vecRange.Y - 
                        cos_lat * vecRange.Z;
         double top_e = -sin_theta * vecRange.X + 
                         cos_theta * vecRange.Y;
         double top_z = cos_lat * cos_theta * vecRange.X + 
                        cos_lat * sin_theta * vecRange.Y + 
                        sin_lat * vecRange.Z;
         double az    = Math.Atan(-top_e / top_s);

         if (top_s > 0.0)
         {
            az += Globals.Pi;
         }

         if (az < 0.0)
         {
            az += 2.0 * Globals.Pi;
         }

         double el   = Math.Asin(top_z / vecRange.W);
         double rate = (vecRange.X * vecRgRate.X + 
                        vecRange.Y * vecRgRate.Y + 
                        vecRange.Z * vecRgRate.Z) / vecRange.W;

         TopoTime topo = new TopoTime(az,         // azimuth, radians
                                      el,         // elevation, radians
                                      vecRange.W, // range, km
                                      rate,       // rate, km / sec
                                      eci.Date);

#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.m_El += Globals.ToRadians((1.02 / 
                                    Math.Tan(Globals.ToRadians(Globals.ToDegrees(el) + 10.3 / 
                                    (Globals.ToDegrees(el) + 5.11)))) / 60.0);
      if (topo.m_El < 0.0)
      {
         topo.m_El = el;    // Reset to true elevation
      }

      if (topo.m_El > (Globals.PI / 2))
      {
         topo.m_El = (Globals.PI / 2);
      }
#endif
         return topo;
      }
Exemple #2
0
        /// <summary>
        /// Returns the topo-centric (azimuth, elevation, etc.) coordinates for
        /// a target object described by the given ECI coordinates.
        /// </summary>
        /// <param name="eci">The ECI coordinates of the target object.</param>
        /// <returns>The look angle to the target object.</returns>
        public TopoTime GetLookAngle(EciTime eci)
        {
            // Calculate the ECI coordinates for this Site object at the time
            // of interest.
            Julian  date      = eci.Date;
            EciTime eciSite   = PositionEci(date);
            Vector  vecRgRate = new Vector(eci.Velocity.X - eciSite.Velocity.X,
                                           eci.Velocity.Y - eciSite.Velocity.Y,
                                           eci.Velocity.Z - eciSite.Velocity.Z);

            double x = eci.Position.X - eciSite.Position.X;
            double y = eci.Position.Y - eciSite.Position.Y;
            double z = eci.Position.Z - eciSite.Position.Z;
            double w = Math.Sqrt(Globals.Sqr(x) + Globals.Sqr(y) + Globals.Sqr(z));

            Vector vecRange = new Vector(x, y, z, w);

            // The site's Local Mean Sidereal Time at the time of interest.
            double theta = date.ToLmst(LongitudeRad);

            double sin_lat   = Math.Sin(LatitudeRad);
            double cos_lat   = Math.Cos(LatitudeRad);
            double sin_theta = Math.Sin(theta);
            double cos_theta = Math.Cos(theta);

            double top_s = sin_lat * cos_theta * vecRange.X +
                           sin_lat * sin_theta * vecRange.Y -
                           cos_lat * vecRange.Z;
            double top_e = -sin_theta * vecRange.X +
                           cos_theta * vecRange.Y;
            double top_z = cos_lat * cos_theta * vecRange.X +
                           cos_lat * sin_theta * vecRange.Y +
                           sin_lat * vecRange.Z;
            double az = Math.Atan(-top_e / top_s);

            if (top_s > 0.0)
            {
                az += Globals.Pi;
            }

            if (az < 0.0)
            {
                az += 2.0 * Globals.Pi;
            }

            double el   = Math.Asin(top_z / vecRange.W);
            double rate = (vecRange.X * vecRgRate.X +
                           vecRange.Y * vecRgRate.Y +
                           vecRange.Z * vecRgRate.Z) / vecRange.W;

            TopoTime topo = new TopoTime(az,         // azimuth, radians
                                         el,         // elevation, radians
                                         vecRange.W, // range, km
                                         rate,       // rate, km / sec
                                         eci.Date);

#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.ElevationRad += Globals.ToRadians((1.02 /
                                                    Math.Tan(Globals.ToRadians(Globals.ToDegrees(el) + 10.3 /
                                                                               (Globals.ToDegrees(el) + 5.11)))) / 60.0);
            if (topo.ElevationRad < 0.0)
            {
                topo.ElevationRad = el; // Reset to true elevation
            }

            if (topo.ElevationRad > (Math.PI / 2.0))
            {
                topo.ElevationRad = (Math.PI / 2.0);
            }
#endif
            return(topo);
        }