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Next: Data Analysis and Simulations of Spectroscopic and Continuum Mapping with the ISO PHOT Interactive Analysis ( PIA)
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PS reprint -
Draper, P. W. 2000, in ASP Conf. Ser., Vol. 216, Astronomical Data
Analysis Software and Systems IX, eds. N. Manset, C. Veillet, D. Crabtree (San Francisco: ASP), 615
GAIA: Recent Developments
P. W. Draper
Starlink, Dept. of Physics,
University of Durham,
DURHAM,
DH1 3LE, U.K.
Abstract:
GAIA, the Graphical Astronomy and Image Analysis Tool, is a derivative
of the ESO Skycat program. It is being actively developed in the U.K.,
by the Starlink project, as a way of providing a graphically rich and
interactive environment for doing 2D astronomy. Skycat provides a
fundamental image, graphics and web catalogue context, which GAIA
extends by providing image analysis tools. This article describes new
tools recently added to GAIA and gives a brief description of the
technologies that underly it.
GAIA
provides an interactive environment for performing graphical 2D
astronomy. Latterly this encompassed things like aperture photometry,
arbitrary region analysis, defect patching, blink comparison,
astrometry gridding, astrometric calibration and celestial coordinate
system switching. More recently these facilities have been extended
to provide contouring, automated object detection and optimal
photometry, as well as more general improvements, such as the ability
to transfer astrometric reference positions between images.
GAIA presents an apparently well integrated interface, but makes
extensive use of existing components - i.e. external
programs. Starlink
applications may be loaded into memory and controlled using a
messaging system. Ordinary command-line programs can be executed as
normal. For instance the processing engine of the photometry toolboxes
is provided by the Starlink package
PHOTOM
and the object detection toolbox uses the SExtractor program.
Figure 1:
Contouring: bottom - optical image of M51 with
overlaid with self-contours. Top - same picture of M51 but with
radio flux contours. The contouring toolbox provides control of the
line colors and widths, individual contours may also be
redrawn. Inter-image registration is performed by the Starlink library
AST
library (Warren-Smith, 2000).
![\begin{figure}
\epsscale{.74}
\plotone{P2-47a_colour.eps}
\end{figure}](img1.gif) |
GAIA, as a program, is a working complex heterogeneous assemblage of
scripting and programming languages, bound together using
Tcl. New Tcl
commands are implemented with code written in C++, C and Fortran. Much
of GAIA is implemented in an object oriented fashion using [incr Tcl]
and by sub-classing the many facilities of Skycat (such as data and
catalogue access). Highly specialized facilities, such as Starlink
format data access and complex astrometry functions, are provided by
reusing existing libraries of functions.
Since GAIA is really a subclass of the VLT/ESO
SkyCat
tool, it shares and extends Skycat's abilities. For instance GAIA can
be remotely controlled and new script-level facilities can be written
as user loadable ``plugins''.
Figure 2:
Object Detection:
GAIA after a pass to detect all the objects on the displayed image has
been made. The objects are actually detected by Emmanuel Bertin's
SExtractor program (run straight-forwardly as a forked process) and
displayed in a Skycat catalogue window. The catalogue window allows
you to make simple queries and inspections of the data, it is also
extended to provide centering on the selected object (as shown).
![\begin{figure}
\epsscale{.90}
\plotone{P2-47c_colour.eps}
\end{figure}](img2.gif) |
Figure 3:
Optimal Photometry:
GAIA performing optimal photometry on an image. All apertures are
constrained to be the same size and can be moved individually. The
darker/red aperture is used to create a PSF profile, other panes of
controls list the complete set of measurements and define the data
characterization. The photometry measurements are made by the
Starlink package
PHOTOM
loaded and controlled by the toolbox.
![\begin{figure}
\epsscale{.60}
\plotone{P2-47b_colour.eps}
\end{figure}](img3.gif) |
Figure 4:
Astrometric Calibration:
GAIA transferring reference positions from a calibrated image (a DSS
image) to an uncalibrated image. The correspondence between the images
is performed using point and click on a selected row.
![\begin{figure}
\epsscale{.75}
\plotone{P2-47d_colour.eps}
\end{figure}](img4.gif) |
Acknowledgments
GAIA is a derivative of the
Skycat
image
display and catalogue browsing tool, developed as part of the
VLT
project at
ESO. Skycat is free software
under the terms of the GNU copyright.
References
Warren-Smith R. F. 2000, this volume, 506
© Copyright 2000 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
Next: Data Analysis and Simulations of Spectroscopic and Continuum Mapping with the ISO PHOT Interactive Analysis ( PIA)
Up: Data Analysis Tools, Techniques, and Software
Previous: Instance-Based Machine Learning Methods for the Prediction of Stellar Atmospheric Parameters
Table of Contents -
Subject Index -
Author Index -
PS reprint -
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