MDI_PLATE_SCALE_ADJUSTMENT(3)

NAME

     MDI_plate_scale_adjustment -- Correct the average  full-disc
     plate scale for focus position, distance and aging

SYNOPSIS

     #include <MDI.h>

     int MDI_plate_scale_adjustment (double *plate_scale, TIME t,
       int *focus, int *quality, double obs_dist)

DESCRIPTION

     MDI_plate_scale_adjustment() provides a  best  estimate  for
     the  average  MDI  full-disc  mode  plate scale based on the
     focus position at the time, the distance of  the  spacecraft
     from  the  sun, and fits to the aging response function (due
     primarily to lensing of the front window).  For a given time
     t  (seconds  since  the SOI epoch), the plate scale, in arc-
     seconds per pixel, is returned, along with the numeric focus
     stop and a numeric quality value (0: not tabulated; 1 provi-
     sional; 2 definitive).  The observer distance (in AU) can be
     optionally  specified;  if it is zero, the value returned by
     soho_obs_dist (t) is used.

     If there is no tabulated fit for the requested time,  or  an
     error  condition  (see  below),  a  default  scale  value of
     1.97784 and a focus stop and quality of 0 are returned.

FILES

     ~CM/tables/calib/geom/scale_corrections
     /usr/local/lib/libMDI.a

SEE ALSO

     soho_obs_dist()

DIAGNOSTICS

     Return values:

     0              normal
     TRUNCATED_FIT       The scale is based on fewer than the normal
                    number of fitting terms in the expansion in
                    observer distance
     EPHEMERIS_GAP       There is no valid ephemeris information for the
                    time requested; the fit is based on an assumed
                    observer distance of 1.0
     CANT_OPEN_FILE      The required correction table could not be found
                    or read; default scale value returned
     BEYOND_TABLE_RANGE  The requested time is outside the range of times
                    for which fits are tabulated; default scale value
                    returned

BUGS

     The focus position is returned as auxiliary information, but
     this  function  and  the table it uses were not designed for
     that purpose and should not be considered definitive.

     If the ephemeris information about the  sun-spacecraft  dis-
     tance  is incorrect, the scale adjustment is also incorrect.
     This is not generally a problem, because there  are  usually
     no observational data to be calibrated when defintive ephem-
     eris data are lacking.