Figure 1: Structure of the WORF system.
Figure 1: PS 9 Kb
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PS reprint
Frossie Economou, Alan Bridger, Phil N. Daly, Gillian S. Wright
Joint Astronomy Centre, Hilo, Hawaii 96720
At the United Kingdom Infrared Telescope (UKIRT), located on Mauna Kea, Hawaii, we are developing a facility that will allow off-site astronomers to eavesdrop during observing, following user requests. When deciding how to implement such a service we identified the following requirements:
The result of the above specification is WORF (WWW Observing Remotely Facility). The reasons we opted for a WWW interface were strongly dictated by the outlined requirements and result in the following benefits:
Moreover it becomes trivial to support multiple remote users. There is a further psychological advantage in that users expect certain delays while downloading images via their WWW browser and so we hope that they would be less likely to get frustrated than if attempting to manipulate software running at the telescope and displaying remotely on their screens over slow network connections.
An obvious use is during service observations by the astronomer on whose behalf the data is being taken. We also envisage its use during allocated time by co-investigators that have not traveled to the telescope but wish to assist in data interpretation and determining observing strategy. We anticipate that it is going to be most useful during runs of CGS4 (the Cooled Grating Spectrometer) both because interpretation of the data can be complex and because use of this instrument places great demands on the observer who could then benefit from assistance from colleagues.
At the front end, WORF consists of a form which the user completes and is served back the requested image or spectrum. This is all the user sees. The heart of the system is a script written in perl5, a language ideally suited to networking tasks and gluing pre-existing software together. The structure of the system is represented in Figure 1. When the user submits a request for an observation, the appropriate data file is read in by the perl script which then plots the data with the requested parameters into a GIF format file and serves it back to the user. Many WWW services operate a similar scheme. Two complementary services are the ability to monitor what files are available (i.e., to what extent data taking has progressed) and the current weather conditions.
Figure 1: Structure of the WORF system.
Figure 1: PS 9 Kb
What was required in our case was a way of reading in the UKIRT data files (which are in the Starlink N-dimensional Data Format) from perl. Rather than writing new code or running up additional software, we instead took advantage of the powerful (though poorly documented) perl extension mechanism (XSUB) to create a perl module for the FORTRAN DSA library which is used by many reduction packages to access NDF files. This approach resulted in considerable savings in both development time and run-time performance and we believe that it is more robust.
Data from UKIRT's CGS4 instrument can be very difficult to interpret in its raw state, since contamination from sky lines is extensive. This is the reason behind the sophisticated automated on-line data reduction system (CGS4DR) that is provided at the telescope. While observations are taking place, CGS4DR generates background-subtracted co-added data, which enable the astronomer to judge the quality of their data. WORF takes full advantage of this existing capability by providing access to files reduced by CGS4DR. In this way the eavesdropper has access to the same level of scientific information as the actual observer. However, the existence of automatic data reduction, while an advantage, is not necessary for WWW eavesdropping; for example the sub-millimeter James Clark Maxwell Telescope (JCMT) are experimenting with implementing this system for their users in a way where the perl program is responsible for some rudimentary data reduction so as to serve meaningful data.
The authors wish to thank Yvonne Pendleton and Mark Drummond (NASA Ames) for the original impetus, Karl Glazebrook (AAO) for his assistance with the DSA module and Henry Stilmack (JAC) for his help with configuring our web server and writing the UKIRT WWW weather monitor. Further information and code for the software mentioned in this paper can be obtained from the following people and sites:
UKIRT is planning to offer WORF to observers in early 1996. Current information can be obtained from http://www.jach.hawaii.edu/~frossie/worf.