def eci2ecef (x, y, z, gmst=None):
  """Converts the given ECI coordinates to ECEF at the given Greenwich
  Mean Sidereal Time (GMST) (defaults to now).
  
  This code was adapted from
  `shashwatak/satellite-js <https://github.com/shashwatak/satellite-js/blob/master/src/coordinate-transforms.js>`_
  and http://ccar.colorado.edu/ASEN5070/handouts/coordsys.doc

  """
  if gmst is None:
    gmst = dmc.toGMST()

  X = (x * math.cos(gmst))    + (y * math.sin(gmst))
  Y = (x * (-math.sin(gmst))) + (y * math.cos(gmst))
  Z = z

  return X, Y, Z
def eci2ecef ( x , y , z , gmst = None ) : if gmst is None : gmst = dmc . toGMST ( ) X = ( x * math . cos ( gmst ) ) + ( y * math . sin ( gmst ) ) Y = ( x * ( - math . sin ( gmst ) ) ) + ( y * math . cos ( gmst ) ) Z = z return X , Y , Z
Converts the given ECI coordinates to ECEF at the given Greenwich
  Mean Sidereal Time (GMST) (defaults to now).
  
  This code was adapted from
  `shashwatak/satellite-js <https://github.com/shashwatak/satellite-js/blob/master/src/coordinate-transforms.js>`_
  and http://ccar.colorado.edu/ASEN5070/handouts/coordsys.doc