ESO SKYCAT TOOL

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 starting SkyCat

See the Skycat FAQ for more information.

skycat features

Open and visualize a variety of FITS images including support for World Coordinate System (WCS), interactive measurement of offsets and other standard visualization functions (SAOimage-like);
Overlay and edit color graphic objects on the image, like `tagging' sources with text, arrows, circles or other graphic elements such as masks;
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 others;
Access local user catalogs.
Save catalog data locally.
Overlay catalog sources on an image;
Interact with Netscape to display more object information when available
Access the observations catalog from the NTT, HST, JCMT, and 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 documents.
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.

Caveats

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 Very Large Telescope (VLT) Project divisions with contributions from the Canadian 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:

Tclutil - Generic Tcl and C++ utilities
Astrotcl - Astronomical Tcl and C++ utilities
Rtd - Real-time Display classes and widgets (see The Messenger, 81, 1995)
Cat - Catalog library and widgets
Skycat - Skycat application and library package

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.

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 malbrech@eso.org.

SkyCat is available as an executable for these platforms:

Solaris-2.5 (SunOS-5.5)
HP-UX-10.20
Linux

The list of changes could be found in this file

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 malbrech@eso.org or to abrighto@eso.org

Acknowledgments

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;

Authors

Allan Brighton, ESO
Thomas Herlin, ESO
Miguel Albrecht, ESO
Daniel Durand, CADC
Peter Biereichel, ESO

Last update: Feb 28, 1996

Send comments to malbrech@eso.org