!
! Procedure SKYDIP.NIC
!
!  This procedure calculates the atmospheric opacity for multibeam
!  bolometer observations.
!
! Normally channel 1 is used for the focus evaluation.
!
var header
define real airmass[nrecord] counts[nrecord] f_eff b_eff
define real len fitx[300] fity[300] a b c d2 d3 e2 e3
define integer ic foc points[3] channel
let channel 1
if ("&1A".ne."A") then
  if (&1.le.n_receivers.and.&1.ge.1) then
    let channel &1
   else
    say "Number of channels is "'N_RECEIVERS'
    say "Skydip can not be done for channel "'&1'
    say "Opacity is calculated for channel 1"
  endif
endif
!
set /def
cl al
set box 4 20 4 16
set mar 20 3 0.1
set exp .8
let airmass 1|sin(el*pi|180)
let counts abs(signal[channel])
lim /var airmass counts
box
label "Air mass" /x
label "Countrate (Hz)" /y
point airmass counts
if (forward_eff.eq.0) then
  let f_eff .85
endif
if (beam_eff.eq.0) then
  let b_eff .45
endif
!
! initialize values for fit
!
let tau (counts[nrecord]-counts[1])|f_eff|   
pause
let focus_pos[1] scan_coord[channel]
for i 1 to nrecord
  let ic 1
  let val1 scan_coord[i]
  let val2 focus_pos[ic]
  for /while (val1.ne.val2)
    let ic ic+1
    if (focus_pos[ic].eq.0) then
      let focus_pos[ic] scan_coord[i]
    endif
    let val1 scan_coord[i]
    let val2 focus_pos[ic]
  next
  let focus_pos[ic] scan_coord[i]
  let counts[ic] counts[ic]+signal[i,channel]
  let points[ic] points[ic]+1
next
let counts counts|points
let d2 counts[1]-counts[2]
let d3 counts[1]-counts[3]
let e2 focus_pos[1]-focus_pos[2]
let e3 focus_pos[1]-focus_pos[3]
let e4 focus_pos[1]^2-focus_pos[2]^2
let e5 focus_pos[1]^2-focus_pos[3]^2
let a (d3*e2-d2*e3)|(e5*e2-e4*e3)
let b (d2-a*e4)|e2
let c counts[2]-a*focus_pos[2]^2-b*focus_pos[2]
let fitx[i] focus_pos[1]+(focus_pos[3]-focus_pos[1])*(i-1)|299
let fity a*fitx^2+b*fitx+c
conn  fitx fity
let foc -nint(b|(2*a))		! microns
let len (user_ymax-user_ymin)|2
let val1 a*foc^2+b*foc+c
if (a.lt.0) then
  draw tex foc 2*val1-user_ymax "\S{" 5 /user
  draw rel foc 2*val1-user_ymax /user
  draw lin foc 2*val1-user_ymax-len /user
  draw tex foc 1.99*val1-user_ymax-len "\\ISFCZ = "'FOC' 2 /user
 else
  draw tex foc 2*val1-user_ymin "\S}" 5 /user
  draw rel foc 2*val1-user_ymin /user
  draw lin foc 2*val1-user_ymin+len /user
  draw tex foc 2*val1-user_ymin+len "\\ISFCZ = "'FOC' 8 /user
endif
draw text .7 -.152 "\\ISCAN : "'SCAN_NUMBER' 6 /box 9       
draw text .7 -.752 "\\ISOURCE : "'SOURCE_NAME' 6 /box 9       
draw text .7 -1.352 "\\ICHANNEL : "'CHANNEL' 6 /box 9