Function:     ircc_mask

Purpose:      Give IRAS detector layout parameters

Category:     IR

File:         ircc_mask.c

Author:       P.R. Roelfsema

Use:          INTEGER IRCC_MASK( DETNO ,     Input   integer
                                 YLOC  ,     Output  real
                                 ZLOC  ,     Output  real
                                 YSIZE ,     Output  real
                                 ZSIZE )     Output  real

              IRCC_MASK   Returns error code:
                           0 - no problem.
                          -1 - not a legal IRAS detector number.
              DETNO       Detector number as given in IRAS Epl. Suppl.
                          DETNO=0 returns the location of the boresight 
                          (0,0) and (roughly) the total size of the IRAS 
                          focal plane.
                          DETNO=-IRCC_BANDNR( INSTRUMENT ) returns the 
                          centroid position and total extent for all detectors
                          in the band defined by INSTRUMENT. (INSTRUMENT=BPHF
                          i.e. boresight returns 0 for all).
              YLOC        Y position of DETNO centroid w.r.t. boresight.
              ZLOC        Z position of DETNO centroid w.r.t. boresight.
              YSIZE       Y size DETNO.
              ZSIZE       Z size DETNO.

Description:

      YLOC and ZLOC are the positions in arcmin of the centers of the 
      detectors relative to the boresight. the detectors in the focal 
      plane have an extent (YLOC-0.5*YSIZE,YLOC+0.5*YSIZE), and 
      (ZLOC-0.5*ZSIZE,ZLOC+0.5*ZSIZE).
      In survey mode images move in the +Y direction over the focal
      plane or, the satellite moves in the -PSI direction on the sky.

      To first order, the nominal detector centre is at:
        THETA(detector) = THETA(boresight) - Z
        PSI  (detector) = PSI  (boresight) + Y/sin(THETA(detector))
      (disregarding proper angular units).

      For higher accuracy (10 arcsec), use ccpsth and IRCC_TIMES.

      The focal plane layout parameters of the survey detectors are
      taken from the Faint Source Survey expl. supp. table
      Appendix II.2


Updates:      Aug 22, 1990: PRR, Adapted from GEISHA
              Nov 26, 1990: PRR, Updated LRS parameters.
              Jan 21, 1991: PRR, Updated LRS parameters.