Class: Orbit::Site

Inherits:
Object
  • Object
show all
Defined in:
lib/orbit/site.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(lat, lon, alt) ⇒ Site

Returns a new instance of Site.



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# File 'lib/orbit/site.rb', line 7

def initialize( lat, lon, alt )
  alt = alt / 1000 #km
  @geo = GeocentricCoordinates.new( OrbitGlobals.deg_to_rad( lat ), OrbitGlobals.deg_to_rad( lon ), alt )
end

Instance Attribute Details

#geo ⇒ Object

Returns the value of attribute geo.



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# File 'lib/orbit/site.rb', line 5

def geo
  @geo
end

Instance Method Details

#altitude ⇒ Object 



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# File 'lib/orbit/site.rb', line 28

def altitude
  @geo.altitude
end

#get_look_angle(eci) ⇒ Object 



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# File 'lib/orbit/site.rb', line 41

def get_look_angle(eci)
       # Calculate the ECI coordinates for this Site object at the time
       # of interest.
       date      = eci.date
       eciSite   = Eci.new(@geo, date)
       vecRgRate = Vector.new(eci.velocity.m_x - eciSite.velocity.m_x,
                                     eci.velocity.m_y - eciSite.velocity.m_y,
                                     eci.velocity.m_z - eciSite.velocity.m_z)

       x = eci.position.m_x - eciSite.position.m_x
       y = eci.position.m_y - eciSite.position.m_y
       z = eci.position.m_z - eciSite.position.m_z
       w = Math.sqrt(OrbitGlobals::sqr(x) + OrbitGlobals::sqr(y) + OrbitGlobals::sqr(z))

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

       # The site's Local Mean Sidereal Time at the time of interest.
       theta = OrbitGlobals.time_to_lmst( date, longitude_rad)

       sin_lat   = Math.sin(latitude_rad)
       cos_lat   = Math.cos(latitude_rad)
       sin_theta = Math.sin(theta)
       cos_theta = Math.cos(theta)

       top_s = sin_lat * cos_theta * vecRange.m_x +
                      sin_lat * sin_theta * vecRange.m_y -
                      cos_lat * vecRange.m_z
       top_e = -sin_theta * vecRange.m_x +
                       cos_theta * vecRange.m_y
       top_z = cos_lat * cos_theta * vecRange.m_x +
                      cos_lat * sin_theta * vecRange.m_y +
                      sin_lat * vecRange.m_z
       az    = Math.atan(-top_e / top_s)

       if (top_s > 0.0)
          az += OrbitGlobals::PI
        end

       if (az < 0.0)
          az += 2.0 * OrbitGlobals::PI
        end

       el   = Math.asin(top_z / vecRange.m_w)
       rate = (vecRange.m_x * vecRgRate.m_x +
                      vecRange.m_y * vecRgRate.m_y +
                      vecRange.m_z * vecRgRate.m_z) / vecRange.m_w

       topo = TopocentricHorizonCoordinates.new(az,         # azimuth, radians
                                      el,         # elevation, radians
                                      vecRange.m_w, # range, km
                                      rate)      # rate, km / 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 += OrbitGlobals::deg_to_rad((1.02 /
                                  Math.tan(OrbitGlobals::deg_to_rad(OrbitGlobals::rad_to_deg(el) + 10.3 /
                                  (OrbitGlobals::rad_to_deg(el) + 5.11)))) / 60.0)
    if (topo.elevation < 0.0)
       topo.elevation = el    # Reset to true elevation
     end

    if (topo.elevation > (OrbitGlobals::PI / 2))
       topo.elevation = (OrbitGlobals::PI / 2)
     end
  #endif
       return topo

end

#get_position(date) ⇒ Object 



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# File 'lib/orbit/site.rb', line 32

def get_position(date)
  return Eci.new(@geo, date)
end

#latitude_deg ⇒ Object 



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# File 'lib/orbit/site.rb', line 20

def latitude_deg
  OrbitGlobals::rad_to_deg( latitude_rad )
end

#latitude_rad ⇒ Object 



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# File 'lib/orbit/site.rb', line 12

def latitude_rad
  @geo.latitude_rad
end

#longitude_deg ⇒ Object 



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# File 'lib/orbit/site.rb', line 24

def longitude_deg
  OrbitGlobals::rad_to_deg( longitude_rad )
end

#longitude_rad ⇒ Object 



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# File 'lib/orbit/site.rb', line 16

def longitude_rad
  @geo.longitude_rad
end

#view_angle_to_satellite_at_time(sat, time) ⇒ Object 



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# File 'lib/orbit/site.rb', line 36

def view_angle_to_satellite_at_time( sat, time )
  sat_position = sat.eci_position_at_time( time )
  topoLook = get_look_angle( sat_position )
end