The Groningen Image Processing SYstem GIPSY
An updated version of the
original paper by J.M. van der Hulst et al.
(update by M. Vogelaar)
Kapteyn Astronomical Institute,
Postbus 800, 9700 AV Groningen, The Netherlands
This paper describes the Groningen Image Processing System which was
built during the late seventies based on earlier systems developed in
Groningen since 1971 and which has been redesigned to run
on a variety of Unix architectures. The general design philosophy, data
structure and user interfaces are described in detail and a brief
overview of the wide range of applications is provided.
With the advent of synthesis radio telescopes in the early seventies a
need for interactive image processing arose. At the Kapteyn Institute
this led to the development of such an interactive software package:
GIPSY, the Groningen Image Processing SYstem (Allen et al. 1985). Over
the years GIPSY has been built up further and a wide variety of new
applications has been added by many staff members and Ph.D. students at
the Institute who designed software in GIPSY to suit their own needs.
At present GIPSY is particularly suited for the processing and analysis
of spectral line synthesis data and Infrared data from the IRAS
satellite. Especially the spectral line analysis has received great
attention, motivated by the extragalactic HI line work at the Kapteyn
Institute. As a result GIPSY has spectral line analysis capabilities which
are quite unique and have not yet been implemented in other image processing
packages. The importance of visualization of truly three dimensional
data sets was recognized early on and has been implemented in several ways.
The developments in computer hardware, in particular the quick
spreading of Unix workstations combining a graphical environment with
fast (and affordable) CPU capabilities have led to a major port and
code overhaul of GIPSY since begin '90. Although all of the principal
been kept, many new features were implemented and this paper will
describe the system as it runs now under Unix and the X-Windows
environment. An additional advantage of the new implementation is its
portability as the system does no longer depend on particular hardware
for its display functions.
In this paper we will describe the general design philosophy, the data
user interface and display software, and give a short summary of application
software present in GIPSY.
General Design Considerations
The main objectives for the design of the second generation GIPSY were
to maintain the original ease of adding application programs, to have
a flexible, self descriptive, multidimensional data structure, to make
use of the de facto standard X11 environment for graphics and image
display and to code the system in ANSI C and the applications in either
ANSI C, standard FORTRAN 77 or COLA (COntrol LAnguage for use with Hermes)
The growth of GIPSY through the years into a versatile image processing
package with a variety of applications, in particular in the area of
spectral line analysis has been possible because of its friendly and simple
environment for programming. Therefore many astronomers have contributed
to the system, adding applications which fulfilled both their own and
general needs. A very crucial ingredient for the ease of programming
has been the modular structure of the system and the use of interfaces
which shield the application programs from other parts of the system such as
the data, and which provide simple tools for communication with the user and
communication with other
tasks. This very important aspect of the system has been kept in the new
design, because the possibility for astronomers and students to contribute
to the system with ease is considered crucial.
The main design requirement for the data structure is the capability to
handle multi-dimensional data. In addition the data-structure must be
self descriptive and support a large variety of coordinate systems. The
latter becomes increasingly important as astronomers use and combine
data from different telescopes in different spectral domains. Few software
systems existing at present support the large variety of coordinate systems
used in astronomy.
The increasing use of workstations dictates the requirement that the
user should be able to make use of the workstation hardware to view his
data. This requirement then implies the use of X11 for image and
graphics display, as X11 has become the standard graphics environment
on workstations of all vendors.
The GIPSY data structure (GDS) is a multi-dimensional crystalline
structure with the possibility of describing the data at all levels.
For the description of data structures GDS makes use of FITS type
keywords. Examples of three dimensional data cubes are:
images at a range of frequencies (wavelengths) resulting from a
spectral line synthesis observation or a processed Fabry-Perot
interferometer observation. In this case the three axes are Right Ascension,
Declination and frequency (wavelength) or velocity. Such a data-cube
can be described at four levels: (i) the top level (here we store
information about e.g. the pointing direction and central velocity, the
three dimensional gridsize, book keeping information describing the
observation); (ii) the intermediate two dimensional levels (here we could
store e.g. the velocity of each individual image in the data cube,
information about whether a plane has been processed (image
reconstruction, continuum subtraction, flat fielding etc.); (iii) the column
and/or row level and (iv) the
pixel level. It will be clear that describing the data at the top level
is most advantageous and gives the least overhead.
The aspects described above appear to be quite unique to GDS and make it
suitable for storing many different kinds of data. It will be clear that
storing image data in a multi-dimensional data structure such as GDS is
relatively straightforward. GDS is, however, flexible enough to store
more complicated data such as sections of scans from the IRAS satellite
covering a certain area of sky, including the time stamps and
The interface layer between GDS and the application programs has the
necessary intelligence built in to address the data cube at
all levels using simple subroutine calls. The interface can be requested to
deliver a pixel, a one dimensional slice in any direction parallel to
the primary axes, a two dimensional slice in any direction parallel to
the primary axes, or a subcube, without having to worry which is the order
in which the data is stored on disk as simple byte streams.
As in the original design of GIPSY, all communication with the user is
handled by a master control program
, described in detail in Allen
and Terlouw (1981). Its main functions are to shield the user from the
operating system and to provide a standard environment for communication
with the tasks in GIPSY. The main fuctionality of the original Hermes
has been kept in the second generation
GIPSY. This includes logging of the session in a file which can be
inspected interactively, the use of a control language and the ability
to construct macros, bookkeeping of inputs for tasks used in the
processing including the possibility to rerun processes with the same
parameters except for those specified
explicitly, and program control using special escape sequences.
The present implementation of Hermes can run on any display terminal,
including X11 terminal windows. The screen is divided onto three areas. The
top area displays the log, which can be inspected page by page, including
a character string search mode. A five line area below displays the
status of the running tasks (at present this can be up to four
simultaneous applications) and the current page of the
log file. A two line area at the bottom is used for user input.
Hermes provides in addition a keyword sensitive help facility which can
be activated at any time and uses an overlay screen. Once called one
obtains information about the keyword for which input is asked. At this
point one can also page through the whole document describing the task
one is running. Exit from the help page brings the terminal back to
the original log/status/input Hermes display.
A new Hermes exploiting the many nice features of the X11 environment is under
A feature which will be developed in addition is remote tasking, e.g. the
possibility to start up a GIPSY task on another processor. This capability for
distributed procressing will be extremely useful in an environment where
processors of different performance are networked together. One can do the
simple operations on a small workstation and start heavy duty tasks on
more powerful machines in the network without having to leave the GIPSY
Display and Graphics
A special application has been developed for the display of images:
GIDS, the GIPSY Image Display System. Up to 64 images can be loaded into
GIDS, depending on the memory size of the workstation or X-terminal one
is using. All display functions are contained within GIDS and are
activated using pushbuttons activated by using a mouse as pointing
device. GIDS makes use of standard X11 calls and is approaches from the
application program level through a library of simple subroutine calls.
The data transfer to (image loading) and from (cursor read out) GIDS is
done via Unix or Internet sockets.
An important aspect of GIDS is that all display functions are integrated
into the window, so that once an image or images are loaded one can control
the display from within the GIDS window using the mouse. It is not necessary
to type in display commands from the user input area of Hermes, other than
the command for loading images.
The GIDS window appears
default as a 512 x 512 display but can be resized. Seven fields
at the top left give status information about which image plane is displayed,
what the cursor position and pixel value at this position are and what
the corresponding image name on disk is. The remaining fields at the
left side of the image are push buttons to control the display.
The built in functions are: (i) display control including a large variety of
color schemes and the additional possibility to provide user defined
color tables (contrast enhancement in this mode is performed by moving
the mouse pointer over the screen where vertical motion controls the
slope and horizontal motion controls the zero point of the transfer
function); (ii) zoom and pan with the useful feature that one can zoom
in x and y independently; (iii) a blinking and movie-loop mode where the
rate is controlled by the x position of the mouse pointer; (iv) a
blotting mode for defining polygons (which could be input to application
programs e.g. for calculating integrated fluxes) using the mouse; and
(v) a split screen mode. The speed of the movie and blink mode depends
on the CPU performance of the workstation. A 512 x 512 movie on a
Sparc station approaches the standard 24 frames per second movie speed,
provided there are no other users on the machine. On a HP 720
workstation the same speed is obtained with a 800 x 800 image
For graphics output such as contour plots GIPSY uses the extensive
PGPLOT library of routines. The plot files can be
displayed in a Tektronix 4010/X11/GIDS window. Graphics capabilities within
GIDS are under development and will in addition allow graphics overlays
on displayed images. Hard copies are made using a PostScript laser printer.
The application programs in GIPSY now constitute over 155000 lines of code,
partly written in ANSI C, partly in FORTRAN 77. The main part of the
system is radio synthesis image processing and includes many standard
algorithms. Examples are conditional or unconditional arithmetic
operations on single images or series of images, convolution,
reprojection (including rotation) onto another coordinate system, pixel
statistics in images, surface photometry routines, and CLEAN (Högbom
1974, Schwarz 1978, Clark 1980). An implementation of the Multi Resolution
Clean (Wakker and Schwarz 1988) is also planned.
A strong emphasis in GIPSY has been on the processing and analysis of
radio spectral line synthesis data and this has led to the coding of a
unique variety of applications for handling three dimensional data (such
as routines to construct maps of velocity versus an arbitrary direction
through the image plane, an average of such maps etc.), for the analysis
of velocity profiles using Gauss components, for the analysis of
velocity fields and for modelling the gas motions in galaxies assuming
realistic mass distributions.
In addition to general and spectral line synthesis applications,
routines to extract Infra Red images from the IRAS raw data base have
been developed in GIPSY, including destriping routines.
GIPSY now runs on the following platforms:
|Alliant FX80||alliant||(Support stopped 01/10/93)|
|HP 300 series||hp9000s300||(Support stopped 30/08/95)|
|HP 700 series||hp9000s700||.|
|Sun 4 systems (<5.0)||sun4||.|
|Sun 4 systems (>=5.0)||sol4||.|
|Convex C2 and C3||convex||.|
GIPSY can be
More information can be requested via e-mail
- Allen, R. J. & Terlouw, J. P.: 1981, Proceedings of the
Workshop on IUE Data Reduction, ed. W. Weis, (Vienna Observatory), 193.
- Allen, R. J., Ekers, R. D. & Terlouw, J. P.:1985, Data
Analysis in Astronomy, ed. V. di Gesù, L. Scarsi, P. Crane, J. H. Friedman
and S. Levialdi, (Plenum Press, N.Y.), 271.
- Clark, B. G.:1980, Astron. Astrophys, 89, 377.
- Högbom, J. A.:1974, Astron. Astrophys. Suppl., 15, 147.
- Schwarz, U. J.:1978, Astron. Astrophys, 64, 345.
- Wakker, B. P. and Schwarz, U. J.:1988 Astron. Astrophys,