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GCROT

GCROT

Name


  GCROT

Purpose


  This function computes, as a function of galactic coordinates, the
  angle between a vector pointing towards the galactic north pole
  and a vector pointing towards the North Celestial Pole. This can
  be used to orient images aligned to ecliptic and galactic
  coordinate systems.

Category


  coordinate systems

Calling Sequence


  result=GCROT(L,B,/DEGREE)

Inputs


  L: Galactic longitude. Radians are assumed unless /DEGREE is set.
  B: Galactic latitude. Radians are assumed unless /DEGREE is set.

Keyword Parameters


  DEGREE: If set, the input and output are given in degrees.
 

Outputs


  The clockwise rotation that aligns the galactic north pole with
  the NCP (in J2000 coordinates). In radians by default.

Restrictions


  This has not been tested for accuracy higher than roughly .5
  degrees. I wouldn't use this to determine the orientation of spectra
  slits or other high precision tasks without testing first.

Procedure


  Uses a spherical trig identity taken from wikipedia.org/wiki/Great-circle_distance
 

Modification History


  Written by: Chris Beaumont, May 2008.
  June 2008 Added /degree keyword. cnb



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