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Graphical Astronomy and Image Analysis tool

Note:This document was written for the Starlink Bulletin when GAIA was first introduced. It does not represent the current state. GAIA now does much more!

GAIA is a new image display tool. What's really "new" about it is that it can be extended to provide new functions and can also be used to control other programs. These abilities make it an ideal tool for attempting to visually enhance the ways in which you work, hopefully resulting in more productive, creative, exploratory (and enjoyable?) analyses.

The way that GAIA is presented at the moment resembles the well known image display tool SAOimage, and indeed it offers much the same functionality (except perhaps for control via pipes). However, the current release should only be viewed as a preliminary one. It's really just intended to exemplify the type of tasks that may be integrated into it. Typically these follow the principle of being controlled by a "toolbox" that defines a single well defined activity or a set of very closely related ones.

This article couldn't possibly give full details of the functions that GAIA offers but a quick rundown goes like:

  • Aperture photometry: this is a highly interactive environment for controlling the positions, sizes and orientations of circular and elliptical apertures, with sky estimates from annuli or other apertures. The measurements can be in either instrumental magnitudes or mean counts (actually this is based on the PHOTOM package).
  • Image patching: this provides the ability to select arbitrary shaped regions on an image and replace them with a surface fit to other regions, together with some artificial noise that makes the whole thing look natural. An ideal way to remove unwanted defects from an image for cosmetic reasons.
  • Image blinking: this allows you to blink through a stack of displayed images, or if your CPU is really sad you can cycle through them by hand.
  • Image regions: this allows you to define arbitrary shaped regions on your image. These can then be extracted or blanked out, or you can see some simple statistics about them.
  • Real time slicing: a profile of the data along a line can be displayed and adjusted interactively. The slice is updated in real time.
  • Image Annotations: using this facility you can draw coloured lines, arrows, circles ellipses, boxes, polygons and text over your images and then print a representation to a postscript file. Line graphics are re-drawn at printer resolution (i.e. this is not a screen dump).
  • Plus of course, pan, zoom, colour table manipulations, continuous data and position readout (for RA and DEC if your images have suitable FITS WCS headers) and display of multiple images.

GAIA will also read NDF and FITS data files, in fact since it uses NDF this also allows it to read other data types (such as IRAF and old FIGARO formats) using "on-the-fly" conversion. Rather than go on any more about GAIA I'll leave the rest of the talking to the accompanying figures.

This figure shows GAIA with the photometry toolbox in action. The apertures it creates can be elliptical or circular, you can also have sky regions in associated apertures rather than in the annuli. Many different apertures can be created at the same time. They can be picked up and moved about the image, resized, rotated etc. Clicking on an image shows the measurement associated with it (naturally you can save and restore all the measurements using text files).

This figure shows GAIA in a slightly different configuration (the pan and zoom windows have been disabled), while displaying a slice through an object. The slice can be moved around the image by dragging the little boxes on the ends of the line (the "grips") and it will be updated in real time (if your hardware is fast enough!).

This figure shows GAIA in another configuration while patching an image (the controls for zooming and showing the data values etc. are now in another window that is not shown). The image on the left is the original and the image on the right the result of replacing the region within the white polygon by a fit to the data in the annulus about it (plus some noise). Using this tool you can replace arbitrarily shaped parts of your image using other arbitrary bits of it to define a fit.

This figure shows GAIA being used to estimate the statistics of an arbitrary region of an image. Using this tool you can also remove and extract such regions. Auto-cropping is useful for removing any large regions of blank pixels about an extracted image. Modified images are displayed in a new window or in the existing window.


GAIA is an extension of the RTD (Real Time Display tool) which has been written at ESO as part of the VLT project. Fortunately RTD has been released as free software under the terms of the GNU copyright, so that others can benefit from it and develop new work that extends it, rather than having to expend effort just in duplication. Many thanks are therefore extended to the development team at ESO (in particular Allan Brighton) who are generous enough with their hard work to make it available in this way.

RTD (for those of you who wonder about such things) is a collection of a Tk canvas widget for displaying images and many [incr Tcl] classes for building up useful applications. It is also used as part of the ESO SkyCat tool ( ).

Where next?

It is hoped that developments of GAIA will continue and that the next area to be tackled will be integrating the new Starlink astrometry library. This is expected to provide the overlaying of astrometric grids, add support for the full range of FITS WCS systems and allow astrometric systems to be interactively fitted to existing data.

Other areas which have been recommended for development are: better support for photometry in data units such as Janskys, the inclusion of routines for automated object detection, galaxy surface photometry and object identification via the WWW. If you have any suggestions to add to this list send them to:

How do I use GAIA?

GAIA is documented in SUN/214, which you can view using the command "showme sun214". You can start it up now (if available on your system) using the command:

    %  gaia [image_file]

Questions or comments to:

Copyright © 2005 Central Laboratory of the Research Councils
Copyright © 2006 Particle Physics and Astronomy Research Council
Copyright © 2008-2009 Science and Technlogy Facilities Council
Copyright © 2009-2013 Peter W. Draper
Last modified: 02-Jun-2016
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