; $Id: //depot/Release/ENVI50_IDL82/idl/idldir/lib/errplot.pro#1 $
;
; Copyright (c) 1983-2012, Exelis Visual Information Solutions, Inc. All
;       rights reserved. Unauthorized reproduction is prohibited.
;

;+
; NAME:
;   ERRPLOT
;
; PURPOSE:
;   Plot error bars over a previously drawn plot.
;
; CATEGORY:
;   J6 - plotting, graphics, one dimensional.
;
; CALLING SEQUENCE:
;   ERRPLOT, Low, High  ;X axis = point number.
;
;   ERRPLOT, X, Low, High   ;To explicitly specify abscissae.
;
; INPUTS:
;   Low:    A vector of lower estimates, equal to data - error.
;   High:   A vector of upper estimates, equal to data + error.
;
; OPTIONAL INPUT PARAMETERS:
;   X:  A vector containing the abscissae.
;
; KEYWORD Parameters:
;   WIDTH:  The width of the error bars, in units of the width of
;   the plot area.  The default is 1% of plot width.
;
;   All keywords to PLOTS are also accepted.
;
; OUTPUTS:
;   None.
;
; COMMON BLOCKS:
;   None.
;
; SIDE EFFECTS:
;   An overplot is produced.
;
; RESTRICTIONS:
;   Logarithmic restriction removed.
;
; PROCEDURE:
;   Error bars are drawn for each element.
;
; EXAMPLES:
;   To plot symmetrical error bars where Y = data values and
;   ERR = symmetrical error estimates, enter:
;
;       PLOT, Y         ;Plot data
;       ERRPLOT, Y-ERR, Y+ERR   ;Overplot error bars.
;
;   If error estimates are non-symetrical, enter:
;
;       PLOT,Y
;       ERRPLOT, Upper, Lower   ;Where Upper & Lower are bounds.
;
;   To plot versus a vector of abscissae:
;
;       PLOT, X, Y        ;Plot data (X versus Y).
;       ERRPLOT, X, Y-ERR, Y+ERR  ;Overplot error estimates.
;
; MODIFICATION HISTORY:
;   DMS, RSI, June, 1983.
;
;   Joe Zawodney, LASP, Univ of Colo., March, 1986. Removed logarithmic
;   restriction.
;
;   DMS, March, 1989.  Modified for Unix IDL.
;       KDB, March, 1997.  Modified to used !p.noclip
;       RJF, Nov, 1997.    Removed unnecessary print statement
;              Disable and re-enable the symbols for the bars
;   DMS, Dec, 1998.    Use device coordinates.  Cleaned up logic.
;   CT, RSI, Jan 2001: Add _REF_EXTRA to pass keywords to PLOTS.
;   CT, RSI, Oct 2004: Add compile_opt idl2 to allow > 32767 error bars.
;   CT, RSI, Oct 2005: Force PSYM=0 in PLOTS, so we ignore !p.psym.
;-
Pro Errplot, X, Low, High, Width = width, $
    DEVICE=device, $   ; swallow this keyword so user can't set it
    NOCLIP=noclipIn, $ ; we use a different default than PLOTS
    _REF_EXTRA=_extra

compile_opt idl2

on_error,2                      ;Return to caller if an error occurs
if n_params(0) eq 3 then begin  ;X specified?
    up = high
    down = low
    xx = x
endif else begin                ;Only 2 params
    up = x
    down = low
    xx=findgen(n_elements(up))  ;make our own x
endelse

w = ((n_elements(width) eq 0) ? 0.01 : width) * $ ;Width of error bars
  (!x.window[1] - !x.window[0]) * !d.x_size * 0.5
n = n_elements(up) < n_elements(down) < n_elements(xx) ;# of pnts

; If user hasn't set NOCLIP, follow what is in !P.
; This is different than PLOTS, whose default is always NOCLIP=1.
noclip = (N_ELEMENTS(noclipIn) gt 0) ? noclipIn : !P.NOCLIP

for i=0,n-1 do begin            ;do each point.
    xy0 = convert_coord(xx[i], down[i], /DATA, /TO_DEVICE) ;get device coords
    xy1 = convert_coord(xx[i], up[i], /DATA, /TO_DEVICE)
    plots, [xy0[0] + [-w, w,0], xy1[0] + [0, -w, w]], $
      [replicate(xy0[1],3), replicate(xy1[1],3)], $
      /DEVICE, NOCLIP=noclip, PSYM=0, _STRICT_EXTRA=_extra
endfor
end