NOW VERSION 2.6.8 (3 July 2001)
skycat is a tool that combines visualization of images and
access to catalogs and archive data for astronomy.
| To use directly the CADC catalogue, set the environment variable
SKYCAT_CONFIG to "http://cadcwww.hia.nrc.ca/skycat/skycat2.0.cfg" before
See the Skycat FAQ for more information.
- Open and visualize a variety of FITS images including support
World Coordinate System (WCS), interactive measurement of
other standard visualization functions (SAOimage-like);
- Overlay and edit color graphic objects on the image, like
sources with text, arrows, circles or other graphic elements
- Display a world coordinates based grid over the image with the
resolution given in arcseconds.
- Display a compass indicating where north and east are in the
image, based on the world coordinates information.
- PostScript color printing of the display (image + graphics);
- Access and load an image from a network server of the Digitized
Sky Survey scans;
- Access and load catalog information from a number of popular
astronomical catalogs like the HST Guide Star Catalog and
- Access local user catalogs.
- Save catalog data locally.
- Overlay catalog sources on an image;
- Interact with Netscape to display more object information when
- Access the observations catalog from the
CFHT Science Archives;
- Access to SIMBAD and NED both as name resolvers as well
as for information on known objects;
- Retrieve preview and other compressed images and decompress them
on the fly.
- Retrieve and plot tabular preview data for a selected object as an X/Y graph.
- Calculate, display and plot the center position, FWHM, angle and other information
for a selected star/object.
- Load compressed images in hcompress, gzip or unix compress format.
- Access SkyCat features from a remote process via socket interface or Tk "send".
- Access image header and data (FITS format) via SysV shared memory or mmap.
- Interact with WWW browser to access catalog documentation and other
- As of skycat-2.0.4, an example Skycat plugin is included in the
source code (also avilable as a separate tar file to go with the single
binary version) that allows saving and reloading of graphics to a file
using either world or image coordinates.
- Load lists of catalogs from sites (ESO, CADC, CDS, local) and and
allow user to select his/her preferred default catalog list.
Things we are working on
- Save canvas graphics as a fits extension on the image file.
- User customizable symbols to "label" objects on the canvas.
- Save user preferences for look-up tables and other settings.
- Add or edit WCS parameters for a given image.
- Astrometry: skycat handles the astrometric
positions by translating pixel positions into equatorial coordinates
(RA, DEC). This translation is based on WCS (World Coordinate System)
FITS keywords that are included in the image header and that give the
astrometric solution for the image. The accuracy of the solution
varies because, in many cases, an approximation is used.
- Colors: If you are running netscape or some other color
intensive applications before you start skycat, you may get
an error message indicating that there are not enough colors left in
the colormap. You can get around this problem by starting netscape
with the "-ncols" option: for example:
netscape -ncols 60 &
You can also control how many colors SkyCat uses via the color
dialog in the View menu.
About the software
skycat was developed by
ESO's Data Management and
Telescope (VLT) Project divisions with contributions from the
Astronomical Data Center (CADC).
The tool was originally conceived as a demo of the capabilities of
the class library that we are developing for the VLT.
This library consists so far of 5 packages:
These constitute the basic building blocks of SkyCat. Early
demonstrations of the tool to users were received so enthusiastically
that we decided to polish things up and produce the current version.
- Tclutil - Generic Tcl and C++ utilities
- Astrotcl - Astronomical Tcl and C++ utilities
- Rtd - Real-time Display classes and widgets
Messenger, 81, 1995)
- Cat - Catalog library and widgets
- Skycat - Skycat application and library package
Java vs Tcl/Tk
Some users might wonder why we did this development in the Tcl/Tk
environment rather than in Java. The main reason is the pragmatic need
to get the functionality implemented in time for when the VLT comes
on-line (mid 1997). However, great care has been taken to develop as
much as possible in the short time with object oriented languages
(C++, [incr Tcl]), having in mind that the future lies in
tele-scripting rather in the distribution of binary code.
SkyCat mailing list
A mailing list has been setup to support a wide collaboration on the
SkyCat/RTD/CatLib project. Many people have shown interest in
participating in such a venture. You can sign up with that list here. A hypermail archive
is also available.
Distribution and support
The SkyCat binaries are freely available to any users who
want to download and use the software at their own risk. Users to wish
to modify the source code should contact email@example.com.
SkyCat is available as an executable for these platforms:
The list of changes could be found in
ESO will maintain the Sun Solaris and HP versions in the longer
term. They are the platforms on which VLT software will run. ESO does
not have the resources to port to and maintain SkyCat on any
other platforms. We will be glad to redistribute any port that other
people or groups may support but decline any responsibility for them.
The software is also available as source code for research and other
non-profit organisations. If you are interested to obtain the package
send us a note.
Please report problems or send suggestions to
firstname.lastname@example.org or to
We very much appreciated practicing wishful programming at
large, i.e. wishing a utility, a function or just a code fragment that
would just do that bit you badly need, then surfing the net, fetching it
and re-using it in our code. Here is an incomplete list of packages
that we either partially re-used or gave a source of inspiration.
- STARCAT contributed many of its internals;
- Tcl/Tk, TclX, BLT, Tix, ET and Itcl give the glue around the C++ classes,
Tk provides the canvas graphics;
- SAOimage lent the WCS lib (now a separate package, provided by courtesy of Doug Mink);
GSC server provided by courtesy of A. Preite-Martinez & F. Ochsenbein;
- SIMBAD and NED client routines allow name resolving;
- The CADC "press" library is used to inflate compressed (hcompress, gzip, ...) images;
- Midas routines are used to calculate the centroid position, FWHM and angle of selected stars/objects;
Allan Brighton, ESO
Thomas Herlin, ESO
Miguel Albrecht, ESO
Daniel Durand, CADC
Peter Biereichel, ESO
skycat is copyright by ESO, 1996. All rights reserved.
Last update: Feb 28, 1996
Send comments to email@example.com