NAME:
	HammerAitoff
 PURPOSE:
	Transforms latitude and longitude to X and Y coordinates in the
	Hammer-Aitoff map projection.
 CALLING SEQUENCE:
	FUNCTION HammerAitoff, Pos  , $
	    degrees	= degrees   , $
	    dabg	= dabg	    , $
	    zero_phase	= zero_phase
 INPUTS:
	Pos	    array[2,n]; type: float
			n locations in the sky
			Pos[0,n]    longitudes
			Pos[1,n]    latitudes in [-90.,90.]
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set then all angles are in degrees (default: radians)

	dabg	    array[3]; type: float; default: none
			Euler angles for a rotation to be applied to
			'Pos' prior to the Hammer-Aitoff projection.
			(see FishEye)
	zero_phase  scalar; type: float; default: none
			Additional offset applied to phase angle
			(see FishEye)
 OUTPUTS:
	Pos	    array[2,n]; type: float
			X,Y Cartesian coordinates (same structure as input array)
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	AngleRange, EulerRotate, IsType, SyncDims, ToRadians
 CALLED BY:
	ColorSkybox, PlotEarthSkymap, PlotEloTimeMap, PlotPolarSkymap
 RESTRICTIONS:
 PROCEDURE:
	The Hammer-Aitoff projection is the format used at NOAA SEL; for
	details, see the book Introduction to Map Projections by Porter W.
	McDonnell Jr.

	Pos[0,*] > 0 has X > 0	Pos[1,*] > 0 has Y > 0
	Pos[0,*] < 0 has X < 0	Pos[1,*] < 0 has Y < 0

	The returned coordinates will be in the range -sqrt(2),+sqrt(2) in the vertical
	(latitudinal) direction and -2*sqrt(2),+2*sqrt(2) in the horizontal (longitudinal
	direction).
 MODIFICATION HISTORY:
	NOV-1992, Tom Davidson (UCSD)
	MAR-1999, Paul Hick (UCSD/CASS); added /degrees keyword)
	JAN-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Added 'dabg' keyword