PRO ucles_norm,w,f,a,r,s,nw,no,sig,pord,sig2

  ; Procedure to merge orders from a  2d echelle frame
  ; into a single spectrum.

  ; Input
  ; w    nw x no  wavelengths
  ; f    nw x no  fluxes

  ; Output
  ; r    nw x no  continuum function
  ; s    nw x no  blaze function
  ; a    nw x no  normalized spectrum

  ; Input
  ; nw            n wavelentghts / order
  ; no            n orders

  ; sig
  ; pord
  ; sig2

  ; Example
  ; flux_norm,w,f,a,r,s,1448,36,40,7,1.2e3,.05
    
  ; remove gross trends

 

  ; collect data from order centre


  colors=GetColor(/Load)
  ordmax = fltarr(no)
  ordcen = fltarr(no)
  nwc = nw/2
  nwd = nw/sig
  wcen = w(nwc,no/2)

  FOR j = 0,no-1 DO BEGIN
    av = moment( f(nwc-nwd:nwc+nwd,j ) )
    ordmax(j) = av(0)
    ordcen(j) = w(nwc,j)
  ENDFOR

  ymax = max ( ordmax )

      window,1
      plot, ordcen,ordmax,yrange=[0,1.2*ymax]


;  IF ( ABS(ordmax(j)-approx(j)) GT sig2 ) THEN ordmax(j) = approx(j)
;  ENDFOR

  ordmax = median(ordmax,5)
  oplot, ordcen,ordmax,color=colors.yellow


; identify outliers
  pn = poly_fit(ordcen-wcen,ordmax,pord,yfit=approx)
  oplot, ordcen,approx,color=colors.red

  FOR j = 1,no-2 DO BEGIN
    IF ( ABS(ordmax(j)-approx(j)) GT sig2*ymax ) THEN ordmax(j) = 0.333 * ( approx(j)+ ordmax(j-1) + ordmax (j+1) ) 
  ENDFOR
  oplot, ordcen,ordmax


    window,2
  plot, ordcen,ordmax,yrange=[0,1.2*ymax]
; identify outliers
  pn = poly_fit(ordcen-wcen,ordmax,pord,yfit=appr2)
  oplot, ordcen,appr2,color=colors.red



  FOR j = 1,no-2 DO BEGIN
    IF ( ABS(ordmax(j)-approx(j)) GT sig2*ymax/2. ) THEN ordmax(j) = 0.333 * ( approx(j)+ ordmax(j-1) + ordmax (j+1) ) 
  ENDFOR
  oplot, ordcen,ordmax,color=colors.blue


    window,2
  plot, ordcen,ordmax,yrange=[0,1.2*ymax]
; identify outliers
  pn = poly_fit(ordcen-wcen,ordmax,pord,yfit=appr2)
  oplot, ordcen,appr2,color=colors.green



  window,0
  plot, ordcen,ordmax,yrange=[0,1.2*ymax]

    r = fltarr(nw,no)
    r = r + pn(0)
    FOR n = 1,pord DO BEGIN
    r = r + double( pn(n)*(w-wcen)^n )
    ENDFOR
    r = r
    oplot,w,r,color=colors.red

    a = f / r

    ; create envelope
    s = median(a,5)
    s = smooth(s,5)

    ; tidy ends
    FOR i = 0,4 DO BEGIN
    s(*,i) = median(s(*,i),8)  
    s(*,i) = smooth(s(*,i),8)  
    ENDFOR
    FOR i = no-4,no-1 DO BEGIN
    s(*,i) = median(s(*,i),8)  
    s(*,i) = smooth(s(*,i),8)  
    ENDFOR

    ; fit polynomials
    bl_ord=9
    FOR i = 0,no-1 DO BEGIN
      bf = poly_fit(w(*,i)-ordcen(i),s(*,i),bl_ord,yfit=sapp)
      s(*,i) = sapp
    ENDFOR

   
    a = a / s  

END