SECTION./ECHE
DEFINE/ECHE  [ordref] [width1,thres1,slope] [defmtd] [defpol]
	define echelle order positions
SECTION./HOUGH
DEFINE/HOUGH  [ordref] [nbord] [hwid] [hough_par] [thresh] [degx,degy] 
              [hot_thres,step] [hough_setup]
	define echelle order positions; automatic detection by Hough transform.
SECTION./SKY
DEFINE/SKY  ima  [nsky]   [possky]  [half_width] 
	defines limits of the sky windows