corner = REPLICATE({ u10:0.0, cd:0.0 }, 4 )
  data = REPLICATE({ u10:0.0, cd:0.0 }, 300 )

; open input file 
  openr, in, 'cd.dig', /GET_LUN

; read upper left corner
  readf, in, FORMAT = '(2F6.0)', dum1, dum2 
  corner(0).u10 = dum1
  corner(0).cd  = dum2 
  
; read lower left corner
  readf, in, FORMAT = '(2F6.0)', dum1, dum2     
  corner(1).u10 = dum1
  corner(1).cd  = dum2
  
; read lower right corner
  readf, in, FORMAT = '(2F6.0)', dum1, dum2     
  corner(2).u10 = dum1
  corner(2).cd  = dum2
  
; read upper right corner
  readf, in, FORMAT = '(2F6.0)', dum1, dum2     
  corner(3).u10 = dum1
  corner(3).cd  = dum2

; read in the points
  i = 0L
  while NOT EOF(in) do begin
    readf, in, FORMAT = '(I5,1X,I5, 2X)', dum1, dum2 
    data(i).u10 = FLOAT( dum1 )
    data(i).cd = FLOAT( dum2 )
    i = i + 1L
  endwhile
  FREE_LUN, in 
  num_obs = i

; convert to real scale 
  cd_scale = 2.5 / ( corner(0).cd - corner(1).cd ) 
  u10_scale = 10.0 / (corner(2).u10 - corner(1).u10 )
  data(*).cd =  ( data(*).cd  - corner(1).cd ) * cd_scale
  data(*).u10 = 2.0 + ( data(*).u10 - corner(1).cd ) * u10_scale  
 
; open output file
  openw, out, 'cd.dat', /GET_LUN

; write output data to file
  FOR i = 0, num_obs-1 DO BEGIN
    printf, out, FORMAT = '(F6.3, 2X, F6.4)', data(i).u10, data(i).cd
  ENDFOR 
    
  FREE_LUN, out
  END