Program:      WEED

Purpose:      Copies snips to an irds (or part of it), or removes snips.
              It will also remove snips which occur more than once in 
              the irds.

Category:     IRAS

File:         weed.c

Author:       Fred Lahuis

Keywords:

    IRSET=     IRDS data set.
               If given, the (snip)subsets represent the snips to be 
               copied. If noting is entered SNIP is asked.

    OUTSET=    If no output set is given the input set will be    [input set]
               overwritten.
    
    SNIP=      Snips to be copied. It is only asked if            [all snips]
               no snips have been entered by way of subsets.
               
    DELSNIP=   Snips to be deleted.                                    [none]
               Has no effect if snips have already been entered through
               subsets or by way of SNIP and is only asked if this is 
               not the case.

  **LENGTH=    All snips with a length less than or equal to this         [0]
               will be removed.
               
  **POS=       Position of the centre of an area for           ['map' centre]
               which the overlapping snips are to be copied.
               If a position but no radius is entered, all snips passing
               through this point are returned.
               If no position is entered the centre as defined in the 
               header is assumed.
               The position has to be given in the same units as those for
               the area defined in the header.
               
  **RAD=       Radius of the area.                                       [-1]
               The radius has to be given in the same units as used for the
               area defined in the header.
               A radius of zero means the snips going through the position
               given with POS.
               A negative radius means no area is defined.
               
  **SDET=      Detector number used in the selection of                   [0]
               snips in an area.
               SDET = 0 corresponds to the boresight.
               
Description:   A combination of inputs also works, e.g. giving SNIP, LENGTH
               and RAD results in copying all snips inside an area of radius 
               RAD around the centre, not specified in SNIP and longer 
               than LENGTH.
               
               At the end WEED copies all header items common to the selected
               snips. For these it has to search the entire header, which
               unfortunately is not always very fast.
               
               WEED also removes all snips occuring more than once in the
               IRDS, i.e. all snips with the same SOP ATT.
               
Comments:

Updates:       August 15 1991:    FL Document created.
               September 10 1991: FL Adjusted to new copyhead_item (faster
                                     than the old one).
                                     Userinfo altered.
               January 8 1992:    FL Bug in the copying of the header 
                                     items removed.