Name

---

      T_GETPSF

Purpose

---

      Driver procedure (for GETPSF) to generate a PSF from isolate stars.

Explanation

---

      Generates a point-spread function from one or more isolated stars.
      List of stars is read from the FITS ASCII table output of T_APER.
      PSF is represented as a sum of a Gaussian plus residuals.
      Ouput residuals are written to a FITS image file.

Calling Sequence

---

      T_GETPSF, image, fitsfile, [ idpsf, psfrad, fitrad, psfname,
                                      /DEBUG, NEWTABLE =]

Inputs

---

      IMAGE - image array
      FITSFILE - scalar string giving name of disk FITS ASCII table. Must
              contain the keywords 'X','Y' (from T_FIND) and 'AP1_MAG','SKY'
              (from T_APER).

Optional Inputs

---

      IDPSF - vector of stellar ID indices indicating which stars are to be
              used to create the PSF. Not that the PSF star should be
              specified *not* by its STAR_ID value, but rather by the its
              row number (starting with 0) in the FITS table
      PSFRAD - the radius for which the PSF will be defined
      FITRAD - fitting radius, always smaller than PSFRAD
      PSFNAME - name of FITS image file to contain PSF residuals,
              scalar string
      GETPSF will prompt for all the above values if not supplied.

Optional Keyword Input

---

      NEWTABLE - scalar string specifying the name of the output FITS ASCII
              table. If not supplied, then the input table is updated with
              the keyword PSF_CODE, specifying which stars were used for the
              PSF.
      DEBUG - if this keyword is set and non-zero, then the result of each
              fitting iteration will be displayed.

Prompts

---

      T_GETPSF will prompt for the readout noise (in data numbers), and
      the gain (in photons or electrons per data number) so that pixels can
      be weighted during the PSF fit. To avoid the prompt, add the
      keywords RONOIS and PHPADU to the FITS ASCII table header.

Procedures Used

---

      FTADDCOL, FTGET(), FTPUT, GETPSF, READFITS(), SXADDHIST, SXADDPAR,
      SXPAR(), WRITEFITS, ZPARCHECK

Revision History

---

      Written W. Landsman STX May, 1988
      Update PSF_CODE to indicate PSF stars in order used, W. Landsman Mar 96
      I/O to FITS ASCII disk files W. Landsman May 96
      Converted to IDL V5.0 W. Landsman September 1997
      Update for new FTINFO call W. Landsman May 2000