;+
; Description :
;   This function computes the expected SAS signals for all four arms, given vectors of X/Y-offsets
;   (in the SAS frame) and solar image radii 
;
; Syntax      : result = stx_compute_sas_signals(xoff, yoff, in_UTC, aperfile, dx=dx, quiet=quiet)
;
; Inputs      :
;   xoff/yoff = vectors (fn. of time) of Sun position in SAS frame [m]
;   solrad    = vector of solar image radii [in m]
;   aperfile  = name (with absolute path) of the file with description of apertures geometry
;
; Output      :
;   result    = a 4xN array that contains the simulated signals for the four arms
;
; Keywords    :
;   dx        = linear step interval [m] - default: 1.e-6
;   quiet     : if set, turn off display of message "Computing signal arm ..."
;   
; History     :
;   2020-01-31, F. Schuller (AIP) : created
;   2020-02-04, FSc : add conversion to nA
;   2020-02-05, FSc : make computation for one arm only
;   2020-06-18, FSc : removed roll angles (included in xoff, yoff)
;   2021-12-16, FSc : pass name (with absolute path) of file with description of apertures as argument
;   2022-01-28, FSc : use solrad instead of in_UTC as input; return only the 4xN array of signals
;
;-
function stx_compute_sas_signals, xoff, yoff, solrad, aperfile, dx=dx, quiet=quiet
  default, dx, 1.e-6
  
  if not keyword_set(quiet) then print,"Computing signal arm A..."
  stx_compute_sas_expected_signal,xoff,yoff,solrad,0, aperfile, sigA, dx=dx
  if not keyword_set(quiet) then print,"Computing signal arm B..."
  stx_compute_sas_expected_signal,xoff,yoff,solrad,1, aperfile, sigB, dx=dx
  if not keyword_set(quiet) then print,"Computing signal arm C..."
  stx_compute_sas_expected_signal,xoff,yoff,solrad,2, aperfile, sigC, dx=dx
  if not keyword_set(quiet) then print,"Computing signal arm D..."
  stx_compute_sas_expected_signal,xoff,yoff,solrad,3, aperfile, sigD, dx=dx

  result = transpose([[sigA],[sigB],[sigC],[sigD]])/1.e9
  return, result
end