NAME:
	Distance2Line
 PURPOSE:
	Calculates the distance of a point to a line for points and lines in the x-y plane
 CATEGORY:
	Tricks
 CALLING SEQUENCE:
	d = Distance2Line(line, point, [,/close])
 INPUTS:
	line		array[2,n]; type: any
			    array of points (x,y coordinates) defining line(s)
			    There should be at least 2 points (n>=2)
	pointx		if only pointx is specified:
			    array[2,m1,m2,...]; type: any
			    points to be tested
			if both pointx and pointy are specified:
	pointx		    array[m1]
			    x-coordinates of points to be tested
	pointy		    array[m2]
			    y-coordinates of points to be tested
			    if /grid is not set then m1 MUST be equal to m2
			    if /grid is set then each x-coordinate is combined with
			    each y-coordinate to cover an m1 x m2 grid of points
 OPTIONAL INPUT PARAMETERS:
	/close_area	adds first point of 'line' array to the end of the array
			    (this effectively 'closes' the curve described by the 'line' array).
	/grid		(only used if both pointx and pointy are used)
 OUTPUTS:
	d		array[n',m1,m2,...]
			    n'=n-1 if /close_area not set
			    n'=n   if /close_area set
 OPTIONAL OUTPUT PARAMETERS:
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	SubArray, SuperArray, SyncDims
 RESTRICTIONS:
	If the 'line' array represents a boundary of an area in the x-y plane with a simple
	enough shape then this procedure can be used to find points inside the closed area.
	If 'line' runs in the clockwise/counter-clockwise direction around the area then all
	distances will be positive/negative for points inside the closed area.
	'Simple enough shape' means that the curvature should be in the same sense everywhere.
 PROCEDURE:
 >	Each pair of points line[*,i] and line[*,i+1] (i=0,n-1) defines a line in the
	x-y plane. If /close_area is set then an additional pair line[*,n], line[*,0]
	is defined.
 >	For each point in the 'point' array the distance to each of the lines is
	calculated. The distance is positive it the point is toward the right of the line when
	looking from line[*,i] to line[*,i+1], and negative on the other side.
 >	If vectors r1 and r2 correspond to points line[*,i] and line[*,i+1], respectively, and
	vector p corresponds to a point then the distance calculated as
	(r2-p)x(r1-p).z/|r2-r1| (z is a unit vector in the z-direction)
 MODIFICATION HISTORY:
	JAN-2000, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	Distance2Sun
 PURPOSE:
	Calulates Electron-Sun distance and angle Sun-Electron-Observer
 CALLING SEQUENCE:
	FUNCTION Distance2Sun, Elo, S, SinChi, degrees=Degrees, grid=grid
 INPUTS:
	Elo	    array; type: float
			elongations of lines of sight
	S	    array; type: float
			Distance along line of sight (i.e. Observer-Electron
			distance) in units of the Observer-Sun distance.
			If /grid NOT set then S should have the same structure
			as 'Elo'. If /grid is set then any array is allowed.
 OPTIONAL INPUT PARAMETERS:
	/degree     if set all angles are in degrees (default: radians)
	/grid	    if set then every element in S is combined with
			every element in Elo
 OUTPUTS:
	Result	    array; type: float
			Sun-Electron distance (same units as S)
	SinChi	    array; type: float
			Sine of angle Sun-Electron-Observer
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	InitVar, SuperArray, ToRadians
 CALLED BY:
	ThomsonLOSStep, ThomsonTang, ThomsonTangMRad
 PROCEDURE:
>	The elongation is the angle between observer-Sun and observer-electron
	direction (Elo = 0 is the direction observer-Sun)
>	Cosine and sine rule in triangle with Sun, Observer and Electron on the corners.
 MODIFICATION HISTORY:
	SEP-1996, Paul Hick (UCSD)
	JUN-2001, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Replacement for old ElSunDistance function
	    Added /grid keyword