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Astronomical Data Analysis Software and Systems IV
ASP Conference Series, Vol. 77, 1995
R. A. Shaw, H. E. Payne, and J. J. E. Hayes, eds.
A Graphical Front End for the WIYN Telescope
Engineering Data System
J. W. Percival
Space Astronomy Laboratory, 1150 University Avenue, Madison, WI
53706 USA
Abstract. The WIYN 3.5 m Telescope Control System features a plat­
form independent, network transparent protocol for distributing telescope
control data to both local and remote sites. This Engineering Data Sub­
system (EDS) can be run in both a burst mode, providing a short (10 s)
sampling of 5­axis servo data at the full 200 Hz bandwidth of the system,
and a slower (1 Hz) archive mode, which is used to monitor and record
control system data during a whole operating session.
The EDS provides over 200 telescope monitors of use to astronomers,
engineers, and system designers including pointing performance data,
servo and mechanical data, and software state data. The general pop­
ularity of this data resource called for a easy way for casual users and
experts alike to select data files and particular telescope monitors, graph
time­series data, and do simple data manipulations such as pan, zoom,
differentiation, and Fourier Transforms. In addition, the inherently dis­
tributed nature of the EDS called for a solution that was portable across
platforms and operating systems that were in common use by any of the
WIYN consortium members.
We have developed a simple but powerful Graphical User Interface
to satisfy these needs. It uses the Tk graphical toolkit language and
common UNIX tools such as shell scripts, grep, and awk to achieve a
lightweight but effective solution to the problem of accessing the EDS.
The data selection portion of the interface is separate from the graphical
manipulation part, which allows both standalone use of the graphing
widget in other applications as well as using it with different data selection
front ends designed for other telescope systems and scientific instruments.
1. Summary of the WIYN Engineering Data Subsystem
The WIYN Engineering Data Subsystem (EDS) is a spacecraft­style telemetry
system that sends telescope telemetry (encoders, currents, voltages, pointing
data, etc.) in a machine­independent format to clients connected across a net­
work. It has these features:
ffl It is content­programmable. The data are arranged into Engineering Data
Records (EDRs) according to data type (e.g., azimuth servo data share a
record, secondary mirror data share a record, etc). Any combination of
EDRs can be turned off.
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ffl It is rate­programmable. Each EDR can be programmed to appear at a
certain rate, (e.g., pointing data once per second, temperatures once per
minute, etc).
ffl A 10­second, 20 Hz ``burst mode'' can capture all pointing data in the outer
pointing loop.
ffl A 10­second, 200 Hz ``burst mode'' can capture all servo data in the inner
pointing loop.
ffl All­night telemetry archives contain every command and error message
that passed through the system, and once­per­second sampling of over 200
telescope telemetry monitors.
The various data file types (2 burst modes, plus archive mode) and large
number of telemetry monitors, not all of which are in each file type, required a
tool to lead engineers and scientists through the dazzling array of choices, and
zero in on what they wanted to see. The design requirements were: that the
software be lightweight, without a large budget; it must be portable, and run on
a number of platforms (i.e. SunOS, DECstations, and Vaxen); and that it must
be flexible, so that quick changes and rapid prototyping is possible.
We chose Tk by John Ousterhout at UCB for the overall GUI capability and
blt graph by George Howlett at AT&T for the graphing widget. For maximum
flexibility, we broke the problem up into two parts: The first is the chooser,
which helps the user select a file type, file name, data type, and data name; and
the second is the grapher, with which the user plots, pans, zooms, and prints
data. The grapher is a separate program, which allows it to be used apart from
the chooser, i.e., as a stand­alone department utility.
2. Off­the­Shelf Construction
Tk and Tcl are ideal for this sort of low­effort, high­impact tool. We already
had differentiators and FFT programs laying about that accepted graph(1)­like
ASCII input, and a graphical scripting language living close to the UNIX shell
allowed a quick, painless integration of these existing tools into readily available
free­ware. The chooser uses simple filename globbing to fill the listbox, and
uses grep(1) and awk(1) to cut and paste the ASCII data file. The grapher
uses standard Tcl string operations to test for two­column (suffix .xy) data or
one­column (suffix .y) data, with an optional .Z denoting compression.
3. tkeds: File Name and Telemetry Chooser
tkeds helps the user choose a telemetry file and a specific telemetry monitor to
examine. The left panel presents the three file types: 20 Hz burst file, 200Hz
burst file, and all­night archive. The left­hand listbox shows all choices for
the selected file type. The listbox changes when the file type changes. The
right panel presents the major data classifications: telescope axes, mount con­
trol electronics, Optical Support Structure, Instrument Adapter Subsystem, and

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miscellaneous data. The right­hand listbox shows the specific telemetry moni­
tors available for the chosen data type. The listbox changes when the data type
changes. The ``plot'' button produces a simple ASCII data file, one coordinate
pair per line, and then launches the graphing application.
Figure 1. The chooser. This application lets the user select a data
file and telemetry monitor, and then launches a graphing application
for data display and processing.
4. tkgraph: Data Graphing Application
tkgraph is the graphing application. Its primary input data format is like the
UNIX graph(1) program: simple ASCII files, one coordinate pair per line. It
also can read ASCII files with one value per line, assuming a simple sequential
abscissa. Finally, compressed versions of each of these file types are allowed.
Plot styles include unconnected points, connected points, and a histogram­style
plot, emphasizing the sampled nature of the data. Data processing includes pan

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and zoom, differentiation, and Fast Fourier Transform. Output options include
PostScript disk files and line printer spooling.
Figure 2. The grapher. This application supports panning and
zooming, as well as differentiation and Fourier transformation. The
data set shown here represents the elevation servo error (85 counts =
1 arcsecond) during a disturbance test in which a 20­lb weight was
suspended then cut from the telescope during tracking.
Figure 3. This figure shows a zoomed detail of the Fourier Transform
of the data in Figure 2. Structure resonances are clearly displayed for
the servo and mechanical engineers.