Class: VORuby::CoordinateSystems::Equatorial::RADecPosition

Inherits:
SpaceTime::SpatialPosition show all
Defined in:
lib/voruby/spacetime/spacetime.rb

Instance Attribute Summary collapse

Attributes inherited from SpaceTime::SpatialPosition

#axis1, #axis2, #axis3

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(ra, dec, distance = nil, equinox = 2000.0, system = :fk5) ⇒ RADecPosition

Create a Position object. ra and dec may be:

1) RightAscension or Declination objects
2) Sexigesimal strings in standard format
3) Strings that looks like decimals
4) Degrees in decimal format.



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# File 'lib/voruby/spacetime/spacetime.rb', line 508

def initialize(ra, dec, distance=nil, equinox=2000.0, system=:fk5)
  self.ra = ra
  self.dec = dec
  self.distance = distance
  self.equinox = equinox
  self.system = system

  super(self.ra, self.dec, self.distance)
end

Instance Attribute Details

#dec ⇒ Object

Returns the value of attribute dec.



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# File 'lib/voruby/spacetime/spacetime.rb', line 500

def dec
  @dec
end

#distance ⇒ Object

Returns the value of attribute distance.



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# File 'lib/voruby/spacetime/spacetime.rb', line 500

def distance
  @distance
end

#equinox ⇒ Object

Returns the value of attribute equinox.



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# File 'lib/voruby/spacetime/spacetime.rb', line 501

def equinox
  @equinox
end

#ra ⇒ Object

Returns the value of attribute ra.



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# File 'lib/voruby/spacetime/spacetime.rb', line 500

def ra
  @ra
end

#system ⇒ Object

Returns the value of attribute system.



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# File 'lib/voruby/spacetime/spacetime.rb', line 501

def system
  @system
end

Class Method Details

.equatorial_to_rectangular(ra, dec) ⇒ Object

Convert RA and Dec in decimal degrees to rectangular coordinates.



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# File 'lib/voruby/spacetime/spacetime.rb', line 581

def self.equatorial_to_rectangular(ra, dec)
  deg_to_rad = Math::PI / 180.0

  x = Math.cos(ra * deg_to_rad) * Math.cos(dec * deg_to_rad)
  y = Math.sin(ra * deg_to_rad) * Math.cos(dec * deg_to_rad)
  z = Math.sin(dec * deg_to_rad)

  return [x, y, z]
end

.rectangular_to_equatorial(x, y, z) ⇒ Object

Convert rectangular coordinates to equatorial coordinates in degrees.



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# File 'lib/voruby/spacetime/spacetime.rb', line 592

def self.rectangular_to_equatorial(x, y, z)
  rad_to_deg = 180.0 / Math::PI

  ra_rad = Math.atan(y/x)
  dec_rad = Math.asin(z)

  ra_rad = ra_rad + 2 * Math::PI if ra_rad < 0.0

  [ra_rad * rad_to_deg, dec_rad * rad_to_deg]
end

Instance Method Details

#==(position) ⇒ Object 



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# File 'lib/voruby/spacetime/spacetime.rb', line 548

def ==(position)
    # Precess the new position object into the same equinox as the receiver.
    position = position.precess(self.equinox, self.system) if position.equinox != self.equinox and position.system != self.system
    self.ra == position.ra && self.dec == position.dec && self.distance == position.distance
end

#angular_separation(position) ⇒ Object

Returns the angular separation between two positions in degrees.



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# File 'lib/voruby/spacetime/spacetime.rb', line 531

def angular_separation(position)
  # Convert to radians
  ra1 = self.ra.value * (Math::PI / 180.0)
  dec1 = self.dec.value * (Math::PI / 180.0)
  ra2 = position.ra.value * (Math::PI / 180.0)
  dec2 = position.dec.value * (Math::PI / 180.0)

  ninety = 90.0 * (Math::PI / 180) # One quarter of a circle (90 degrees) in radians

  sep = Math.acos(
    Math.cos(ninety - dec1) * Math.cos(ninety - dec2) +
    Math.sin(ninety - dec1) * Math.sin(ninety - dec2) * Math.cos(ra1 - ra2)
  )

  return sep * (180.0 / Math::PI)
end

#precess(to_equinox = 2000.0, system = :fk5) ⇒ Object

Precess the position to the specified equinox. The constants for the precession matrix and general algorithm are taken from the IDL astro routines PREMAT and PRECESS. Notes: Accuracy of precession decreases for declination values near 90 degrees. Should not be used more than 2.5 centuries from 2000 on the FK5 system (1950.0 on the FK4 system).



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# File 'lib/voruby/spacetime/spacetime.rb', line 558

def precess(to_equinox=2000.0, system=:fk5)
  if self.equinox != to_equinox or self.system != system
    deg_to_rad = Math::PI / 180.0

    from_components = Matrix.row_vector(RADecPosition::equatorial_to_rectangular(self.ra.value, self.dec.value))
    precession_matrix = Equatorial::precession_matrix(self.equinox, to_equinox, system)
    to_components = from_components * precession_matrix
    ra, dec = RADecPosition::rectangular_to_equatorial(to_components[0, 0], to_components[0, 1], to_components[0, 2])

    return RADecPosition.new(ra, dec, self.distance, to_equinox, system)
  else
    return self
  end
end

#to_s ⇒ Object 



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# File 'lib/voruby/spacetime/spacetime.rb', line 573

def to_s
  coords = "#{self.ra}, #{self.dec}"
  coords << ", #{self.distance}" if self.distance

  coords
end