                     The STSDAS gasp package
                          stsdaspkg$gasp
                            April 1991

This directory defines a package to access the compact disk (CD-ROM)
format Hubble Space Telescope Guide Star Catalog.  The two volumes of
the CD-ROM consist of FITS files containing tables of guide star
coordinates separated by fields within limits of right ascension and
declination.  Some of the tasks depend on hardware and software to read
the CD-ROM not available on all systems.  Some tasks require an image
display server (imtool or SAOImage) available to IRAF.  Other tasks are
independent of these system configurations.

See the package help (help gasp) to find out how to gain access to the
disks.

The tasks in this package: 

  o  Load a CD-ROM index table to local magnetic disk and convert the
  FITS file to an STSDAS table.  There is a copy of the index table on
  both disks.  (stgindx)

  o  Search the index table to locate those files containing guide
  stars whose coordinates are within specified limits.  The input
  consists of the center and width of the user's region.  The output is
  a list containing the path and file names of the guide star region
  files residing on the CD.  (sgscind)

  o  Copy the files containing the selected fields from the CD to
  magnetic disk files and convert the FITS table(s) into STSDAS
  table(s).  The input consists of a list of files on the CD (the
  output of the previous task) and the output is the STSDAS tables and
  a list of these tables.

  o  Extract the guide stars within the specified coordinate and
  brightness limits from the list of field tables.  The output is a
  table containing the guide star coordinates within the specified
  region.  (extgst)

  o  Display an image corresponding to the user's field;  either a
  guide star plate scan or the user's image.  This image must have a
  preliminary transformation to convert image pixel numbers to
  celestial coordinates.

  o  Compute image pixel coordinates from celestial coordinates based
  on a given coordinate transformation.

  o  Allow the user to interactively identify guide stars with objects
  in the displayed image to improve the intitial coordinates.  The user
  points to objects manually, and specifies the correct position by
  pointing there as well. Various keystrokes perform specific functions
  such as deleting guide stars or performing a plate solution.
  (intrep)

  o  Improve the identified positions from analysis of the sub-image
  near the identified positions.

  o  Perform a plate solution between the identified plate coordinates
  and the guide star catalog coordinates.

  o  Compute coordinates of targets interactively specified by the user
  on the image using the plate solution coefficients.


Separate tasks implement various parts of the package because of the
nature of the interfaces and a single script, targets, brings them
together in one task.
