pro circle_draw,np,x,y
; make a set of X & Y points that will form a circle (i.e., plot,x,y),
; for the input NP # of points, the range in X & y is -1 to 1
np2 = np/2.
x = (findgen(np+1) - np2) / np2
y = sqrt(1^2 - x^2)
x = [x,reverse( x)]
y = [y,reverse(-1*y)]
;- done
return
end