the ESO SkyCat Tool

SkyCat is a tool that combines visualization of images and access to catalogs and archive data for astronomy.

See the SkyCat FAQ and the SkyCat Programmer's Manual for more information.

You can download the latest Skycat version here.

### SkyCat features

- Display FITS images, with support for the World Coordinate System (WCS), interactive measurement of offsets, and other standard visualization functions (SAOimage-like).

- Overlay and edit color graphic objects on the image, `tagging' sources with text, arrows, circles, or other graphic elements.

- 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 images from network image servers, such as the Digitized Sky Survey (DSS).

- Select previously viewed images from a history menu and catalog. The cut levels, color scale algorithm and colormap settings are remembered for each image.

- Access and load catalog information from a number of popular astronomical catalogs, such as the HST Guide Star Catalog and many others.

- Create, search and edit local user catalogs.

- Save catalog data locally.

- Overlay catalog sources on an image, taking object size and orientation into account.

- Interact with Netscape to display more object information when available

- Access the observations catalog from the NTT, HST 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 and save 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.

- Support for dynamically loaded skycat plugins, such as the GAIA plugin, that add new features or modify existing ones.

- Load lists of catalogs from other sites (ESO, CADC, CDS, local) and and allow users to select a 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.

- Add a user preferences dialog.

- Add or edit WCS parameters for a given image.

- Add support for 16 and 24 bit color currently requires that the display support an 8-bit pseudocolor X visual).

### 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 some color flashing when you move the mouse in and out of the SkyCat image window. This is because SkyCat is using a private colormap to get enough colors to display the image. 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.

The Skycat sources currently consist of five 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)

- Catlib - Catalog library and widgets

- Skycat - Skycat application and library package

You can get the sources from the skycat ftp directory. All of the required packages are always included in the tarfile.

#### 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 was the pragmatic need to get the functionality implemented in time for the VLT to come on-line (mid 1998). However, great care has been taken to develop as much as possible 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 who wish to modify the source code should contact malbrech@eso.org.

SkyCat is available as an executable for these platforms:

Solaris (SunOS-5.5.1)
HP-UX-10.20
Linux

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 available as source code for research and other non-profit organizations. 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 automatically compress and decompress (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)

SkyCat is copyright by ESO, 1996. All rights reserved.

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Last modified: Thu Oct 1 20:26:01 MEST 1998