C+
C NAME:
C	ThomsonMidpoint
C PURPOSE:
C	Calculate position along line of sight where the integrated
C	intensity is half of the intensity integrated along the
C	entire line of sight
C CALLING SEQUENCE:
	function ThomsonMidpoint(ScSun,Elo,U)
C INPUTS:
C	ScSun		real	distance of spacecraft from Sun (solar radii)
C	Elo		real	elongation of s/c line of sight (l.o.s.) in degrees.
C				Elo=0 is the direction to the Sun
C OUTPUTS:
C	ThomsonMidpoint	real	point on l.o.s. where intensity is half the total
C				integrated intensity
C INCLUDE:
	include		'math.h'
C EXTERNAL:
	external	ThomsonMid
C CALLS:
C	nrZbrac, nrZBrent, ThomsonSetupMid, BadR4
C RESTRICTIONS:
C PROCEDURE:
C MODIFICATION HISTORY:
C	JAN-1997, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
C-
	    real	ScSun
	    real	Elo
	    real	U

	real		nrZBrent
	logical		nrZbrac

	ThomsonMidpoint = BadR4()

	SHi = ThomsonSetupMid(ScSun,Elo,U)

	SHi = ScSun*max(0.1,cosd(Elo))		! Distance to plane of sky
	if (nrZbrac(ThomsonMid,0.,SHi,1)) ThomsonMidpoint = nrZBrent(ThomsonMid,0.,SHi,MATH__TINY)

	return
	end