!------------------------------------------------------------------------ 
! LEVELS.GREG 
! Procedure to define contour levels for multichannel image 
! Variables defined in DEFINE.GRAPHIC 
! S.Guilloteau 15-Oct-1992 
!------------------------------------------------------------------------ 
define real range expo mant tmin tmax
define integer n1 n2 
! 
if spacing.lt.0 then 
  return 
endif 
if (&1%extrema.eq.0.or.(&1%min.eq.&1%max)) then   ! means no extrema section 
  compute tmin min &1 
  compute tmax max &1 
!  let &1%extrema 2 
else
  let tmin &1%min
  let tmax &1%max
  if tmin.eq.tmax then
    say "F-LEVELS, &1 has no range: max = min = " 'tmin'
    break
  endif
endif 
if (spacing.eq.0) then 
  let range = log10(tmax-tmin)
  let expo = int(range+20.)-21 
  let mant = range-expo-1 
  if (mant.lt.0.25) then 
    let true_spacing 10**expo 
  else if (mant.lt.0.60) then 
    let true_spacing 2.*10**expo 
  else if (mant.lt.0.90) then 
    let true_spacing = 5.*10**expo 
  else 
    let true_spacing = 10**(expo+1) 
  endif 
else 
  let true_spacing = spacing 
endif 
let n1 nint(tmin|true_spacing) 
let n2 nint(tmax|true_spacing)
if (n1.lt.0.and.n2.gt.0) then 
  levels true_spacing*n1 to -0.95*true_spacing by true_spacing true_spacing to true_spacing*(n2+0.05) by true_spacing 
else if (n1.gt.0) then 
  let n1 max(n1,1) 
  levels true_spacing*n1 to true_spacing*(n2+0.05) by true_spacing 
else if (n1.lt.0.and.n2.lt.0) then
  let n1 -max(-n1,1) 
  levels true_spacing*n1 to true_spacing*(n2+0.05) by true_spacing 
else if (n1.lt.0.and.n2.eq.0) then
  let n1 -max(-n1,1) 
  levels true_spacing*n1 to -0.95*true_spacing by true_spacing 
else if (n1.eq.0.and.n2.ne.0) then
  levels true_spacing*(n1+1) to true_spacing*(n2+0.05) by true_spacing 
endif 
let level_min true_spacing*n1 
let level_max true_spacing*n2