% @(#)hough_eche.hlq	17.1.1.1  (ESO)  01/25/02  17:50:36
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1990 European Southern Observatory
%.IDENT      hough_eche.hlq
%.AUTHOR     PB, IPG/ESO
%.KEYWORDS   MIDAS, help files, HOUGH/ECHELLE
%.PURPOSE    On-line help file for the command: HOUGH/ECHELLE
%.VERSION    1.0  08-FEB-1991 : Creation, PB
%----------------------------------------------------------------
\se
SECTION./ECHE
\es\co
HOUGH/ECHELLE                                  26-MAR-1995  PB
\oc\su
HOUGH/ECHELLE input [scan] [step,nbtr] [nbord] [flags] [hwid] [thres] [params]
	perform Hough transform and orders detection on a flat-field frame
\us\pu
Purpose:   
           This command is a low-level command, called by DEFINE/ECHELLE
           to perform the automatic detection of orders on a correctly
           contrasted frame. The method involves Hough transform and 
           cluster detection algorithms.
\up\sy
Syntax:    
           HOUGH/ECH input [scan] [stp,nbt] [nbo] [flags] [hwid] [thres] [par]
\ys\pa
           input     =  Name of order reference frame. The frame must be
                        at standard orientation.
\ap\pa
           scan      =  low,high. Limits in pixels of the scanned part
                        of the image. Pixels outside these limits in
                        input frame do not participate to the Hough
                        transform.
\ap\pa
           stp,nbt   =  step and number of traces for Hough transform.
                        Only (nbtr) columns of the input image are transformed,
                        separated by (step) pixels, and evenly distributed
                        around the central column.
\ap\pa
           nbo       =  number of orders to be detected. If the value 0
                        is given, the order detection detects a minimum
                        of 8 orders by order of brightness, then stops
                        when no order brighter than a fraction (0.2) of
                        the brightest order can be found.
\ap\pa
           flags     =  XYZ.
                        X can be: H to perform the Hough transform;\\
                                  N to skip it (middummh.bdf is taken as HT).\\
                        Y is the order detection method (see note).\\
                        Y can be L for low contrast method;\\
                                 M for medium contrast method;\\
                                 H for high contrast method;\\
                                 N to skip the order detection.\\
                        Z can be V to visualize the intermediate steps;\\
                                 N for no visualization.
\ap\pa
            hwid     =  Half width of the orders. A value is required
                        if the detection method is low_contrast. If no
                        value is provided, the half-width is measured on
                        the frame. In medium_contrast method, the
                        half width is measured for the first detected
                        (or brightest) order and used for next orders.
                        In high_contrast method, the half width is
                        mesaured independently for each order.
\ap\pa
            thres    =  t1,t2,t3,t4.\\
                        t1,t2 are unused.\\
                        t3 is the hot pixel threshold. Pixels higher
                           than t3 are ignored in Hough transform.\\
                        t4 is the relative threshold for the centering
                           of detected clusters.
\ap\pa
            par      =  cluster,slope_mini,slope_maxi,step_slope,step_orig\\
                        cluster (default : 0.2) is the cluster detection
                        constant involved in the decision of terminating 
                        the order detection.
                        slope_mini (default : -0.1) is the minimal slope,
                        boundary of the Hough transform image.
                        slope_maxi (default : 0.4)  is the maximal slope,
                        boundary of the Hough transform image.
                        step_slope (default : 0.005) is the increment of
                        slope corresponding to 1 pixel along X axis 
                        in the Hough transformed image.
                        step_orig (default : 1.0) is the increment of
                        ordinate origin corresponding to 1 pixel along Y axis 
                        in the Hough transformed image.
\ap\no 
Note:
            For a description of the algorithm, see Ballester, 1994,
            Astron. Astrophys., 286, pp. 1011-1018.
\on\exs
Examples:
\ex
            HOUGH/ECHELLE flat  5,320  10,50  0  HMV 0 
\xe \sxe