function check_circularity,clnmap,flevel,PLOT=plot
; Returns a measure of the circularity of the flevel contour
; plevel = fraction of maximum

; Gets the flevel contour using 
; the structure produced by keyword PATH_INFO in IDL's contour
; returns a measure of circularity
; (max(radius)-min(radius))/(max(radius)+min(radius))
; For a 2:1 ellipse, measure=0.33
; for a 1.5:1 ellipse, measure=0.20
; for a 1.25:1 ellipse, measure=0.11

if (flevel LE 0 OR flevel GE 1.0) then message,'flevel out of range'

CONTOUR, clnmap, level=[flevel]*max(clnmap),PATH_XY=xy, PATH_INFO=info
ncontours=n_elements(info)
x=reform(xy(0,*))
y=reform(xy(1,*))

if keyword_set(PLOT) then plot,[x,x[0]],[y,y[0]];,xra=[0,1],yra=[0,1]
xbar=mean(x) & ybar=mean(y)
radius=sqrt((x-xbar)^2+(y-ybar)^2)

measure=(max(radius)-min(radius))/(max(radius)+min(radius))
return,measure                     
end


; TEST

xx=(findgen(64)-32)#replicate(1,64)
yy=transpose(xx)
a=8 & b=10
a=16 & b=20
;a=0.8*a & b=0.8*b
z=2.^(-(xx/a)^2-(yy/b)^2)
mea=check_circularity(z,0.5,/plot)
print,mea

end