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Kulkarni, P., Kembhavi, A., & Kale, S. 2003, in ASP Conf. Ser., Vol. 314 Astronomical Data
Analysis Software and Systems XIII, eds. F. Ochsenbein, M. Allen, & D. Egret (San Francisco: ASP), 346
VOTable JAVA Streaming Writer and Applications.
Pallavi Kulkarni, Ajit Kembhavi
Inter University Center For Astronomy And
Astrophysics (IUCAA), Pune.
Sonali Kale
Persistent Systems Private Limited (PSPL), Pune.
Abstract:
Virtual Observatory related tools use a new standard for data
transfer called the VOTable format. This is a variant of the xml
format that enables easy transfer of data over the web. We
describe a streaming interface that can bridge the VOTable format,
through a user friendly graphical interface, with the FITS and
ASCII formats, which are commonly used by astronomers. A streaming
interface is important for efficient use of memory because of the
large size of catalogues. The tools are developed in JAVA to
provide a platform independent interface. We have also developed a
stand-alone version that can be used to convert data stored in
ASCII or FITS format on a local machine. The Streaming writer is
successfully being used in VOPlot (See Kale et al 2004 for a
description of VOPlot).We present the test results of converting
huge FITS and ASCII data into the VOTable format on machines that
have only limited memory.
VOTable java Streaming Writer is an API library for writing
data in VOTable format. Streaming support is provided to deal with
very large VOTable files without running out of memory. The
writer does not create a tree structure in memory, so that the
memory requirement is substantially reduced and very large
VOTables can be written.
This is a tool for converting ASCII or FITS files to VOTable
format. For ASCII files, it supports both ASCII files with column
delimiters and ASCII files with fixed width columns. For FITS
files, it supports FITS ASCII and binary tables. A number of
useful data processing, browsing and visualization tools are
available to deal with data in the VOTable format. But, most of
the astronomy legacy data exists in the form
of ASCII catalogues and FITS tables. To be able to use the new VOTable packages on legacy data,
it is necessary to have a converter which transforms that data to the VOTable format.
Tools are also needed to transform the outputs generated by various application packages to the VOTable format.
We describe such a tool here.
Figure 1:
Screenshot 1
![\begin{figure}
\epsscale{1.0} \plotone{P3-25_f1.eps} \end{figure}](img1.gif) |
The tool can handle two types of ASCII files:
- ASCII files with column delimiters.
- ASCII files with fixed width columns.
The tool first determines which of the two types the ASCII file
is. It then determines the delimiter, or the width of individual
column depending upon the file type. It reports to the user the
number of columns detected, and this number can be changed if
required in special cases. Finally, it determines the data type of
individual columns by scanning the first few lines in the file and
displays the file metadata which can be edited.
When the file is converted to VOTable format, it is written to output stream using the VOTable Java Streaming Writer.
The tool works in streaming mode by reading the ASCII file one line at a time and writing the VOTable one row at a time. It can therefore be
used to convert big ASCII files to VOTable files without running
out of memory.
The tool makes use of nom.tam.fits library to read FITS files.
Metadata is read from the headers of individual Header Data Units.
Metadata is displayed to the user for confirmation and it can be
edited as well. After the FITS tables are converted to VOTable,
the tool makes use of the VOTable Java Streaming Writer to write
the data to the output stream.
Figure 2:
Screenshot 2
![\begin{figure}
\epsscale{1.0} \plotone{P3-25_f2.eps} \end{figure}](img2.gif) |
VOPlot is a tool for visualizing astronomical data. It is an
application for plotting different astronomical graphs using data
stored in VOTable format. VOPlot makes use of VOTable Java
Streaming Writer to export the data in VOTable format. See Kale et
al (2004) for a description of VOPlot.
- The tool was found to require about 8.03 minutes to convert
the Tycho-II catalogue with 1058332 rows having size 354MB on a
P-IV machine with 384MB RAM.
- The tool was found to require about 0.7 minutes to convert the
Burbidge catalogue with 22484 rows having size 2.29MB on a P-IV
machine with 384MB RAM.
- The tool was found to require about 0.016 minutes to convert
the UGC catalogue with 12939 rows having size 1.22MB on a P-IV
machine with 384MB RAM.
- The tool was found to require about 0.1276 minutes to convert
the hd catalogue with 100000 rows having size 7.16 MB on a P-IV
machine with 384MB RAM.
- Inter University Center for Astronomy and Astrophysics -
http://www.iucaa.ernet.in
- Persistent Systems Private Limited -
http://www.persistent.co.in
- Centre de Donnés astronomiques de Strasbourg -
http://cdsweb.u-strasbg.fr
- VOTable - http://vizier.u-strasbg.fr/doc/VOTable/
References
Kale, S. 2004, this volume, 350
© Copyright 2004 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
Next: VOPlot: A Toolkit for Scientific Discovery using VOTables
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