;------------------------------------------------------------------
;+
; NAME:
;	POLSTACK
; PURPOSE:
;
;	     This program adds an image to a composite solar map.
;	It works for images of type FLOAT (i.e. standard IDL floating pt.)
;	only.
;
;	     If the stack is "blank" (all pixels less than -30000)
;	the new image is copied and becomes the stack.
; CATEGORY:
;	POLAR
; CALLING SEQUENCE:
;	POLSTACK,stackimage,newimage
; INPUTS:
;	stackimage = image containing composite map.
;	             A "blank" stack can be created with the command
;	             newstack = REPLICATE(-32000,xsize,ysize)
;	newimage   = image to add to stack.
; KEYWORD PARAMETERS:
; OUTPUTS:
;	The stackimage is modified.
; COMMON BLOCKS:
; NOTES:
;	The newimage must be the same dimensions as the stackimage.
; MODIFICATION HISTORY:
;	J. Varsik,	27 Nov. 1995 --- Port from IRAF task
;-
;-------------------------------------------------------------------

pro polstack,stack,new,help=help

    ; Display IDL header if help is required.
    if (keyword_set(help)) then begin
      get_idlhdr,'polstack.pro'
      goto,finishup
    endif

    if (n_elements(stack) eq 0) then begin
;        stack is undefined
         isize = size(new)
         stack = make_array(isize(1),isize(2),/FLOAT,VALUE=-32000.0)
    endif

    newindex = where((new ge -30000 and new le 30000),ncount)
    if (ncount ne 0) then stack(newindex) = new(newindex)

    newindex = where((new gt 30000 and stack lt -30000),ncount)
    if (ncount ne 0) then stack(newindex) = new(newindex)

    finishup:

    return
end