NAME:
	GCIRC1  
based on GCIRC
 PURPOSE:
	Computes rigorous great circle arc distances.
 CALLING SEQUENCE:
	GCIRC1, U, RA1, DC1, RA2, DC2, DIS, dra, ddec
 INPUTS:
	U    -- Describes units of inputs and output:
		0:  everything radians
		1:  RAx in decimal hours, DCx in decimal
			degrees, DIS in arc seconds 
	RA1  -- Right ascension of point 1
	DC1  -- Declination of point 1
	RA2  -- Right ascension of point 2
	DC2  -- Declination of point 2
   OUTPUTS:
	DIS  -- Angular distance on the sky between points 1 and 2
		See U above for units;  double scalar  
       DRA  -- Angular distance in RA
       DDEC -- Aungular distance in DEC
   PROCEDURE:
	Ordinary spherical trig formula.
   NOTES:
	Either RA1,DC1 or RA2,DC2 (but not both coordinates) can be vectors.
	In this case DIS is a vector giving the angular distance between
	each of the vector coordinates to the scalar coordinate
   MODIFICATION HISTORY:
	Written in Fortran by R. Hill -- SASC Technologies -- January 3, 1986
	Translated from FORTRAN to IDL, RSH, STX, 2/6/87
	Vector arguments allowed    W. Landsman    April 1989
       
       return value for Delta RA (dra) and Delta DEC (ddec) 
       See U above for units;  -------- Paolo Ciliegi June 1997

(See /home/xmmssc/soft/idl/pro/match/gcirc1.pro)