The plot device is changed, or initially set up, using the cpd command
(change plot device). This is usually specified as
cpd /dev
where ``dev" specifies the plot device and must be preceeded by a ``/".
A list of supported plot devices can be obtained by typing cpd ?. Once a
plot device has been defined in this way, it will be used for the current
and subsequent sessions.
Note: unlike most BROWSE commands there must be A SPACE between the /
and the command cpd.
The plot can be written to a postscript file by specifying the filename
as follows:
CMA_SOURCES_DEC > cpd file/ps
If a default plot device has not been defined, the user will be asked
to provide one each time a graphics routine is called.
The following describes in more detail some of the more popular graphics
devices:
VT - The vt graphics standards, such as the VT200 and 300 series, are
supported by the /vt option.
Tektronics - All Tektronics terminals use the /te option.
VersaTerm_Pro - The /retro option is a Tektronics, but with the ability
to switch automatically from the text to graphics window.
X windows - The plot device /x11 provides X-windows display. This is
available only if the connection is directly via decnet or TCP/IP. If
BROWSE is used via a gateway, the cpd /x11 option cannot be used. Note
that when using X windows, it will be necessary to authorize the
server workstation before a plot can be made.
IRAF/SUN users - IRAF users can use the GTERM window and the
option /gterm.
Postscript files - There is a postscript driver that is invoked simply by
giving a file name, such as cpd ngc4151. This will send the subsequent
plot to the file ngc4151.ps. Only one plot per file is allowed. This
postscript file can then be mailed to the user's computer.
HP terminals - HP terminals (such as HP2393A) use /hq.
A better visualisation of the parameter values can be obtained by plotting one
against another. The ps (plot sample) command allows up to six parameters
to be plotted. It is also possible to use ps to obtain ``aitoff" projections
for coordinate plots, as well as binned histograms of parameter values. This
chapter explains how to use the ps command.
The names of the parameters to be plotted can either be specified on the
command line, such as ps par1 par2 etc., or given in response to questions.
The following is a typical example of a plot session that plots the time
against count rate for all the 3c382 filter 7 observations.
CMA_SOURCES_DEC 39:24> cpd /te
CMA_SOURCES_DEC 39:24> ps/plt time count
Plotting to /te
Plot will appear on terminal.....
CMA_SOURCES_DEC 39:24>
When the /logy and/or the /logx qualifiers are specified, then
the y and/or x-axes use logarithmic scales.
Coordinates can be plotted by simply using ps ra dec. This plots
the positions of the sample or subsample. However, this will not take
into account the spherical nature of the sky and, for large areas, an
equal area projection is better. This can be obtained with the /aitoff
qualifier. The ``hammer" equal area projection is also available
by using /ham instead of /ait.
The default is to use galactic coordinates. The /celestial qualifier
uses RA and Dec, and the /ecliptic uses ecliptic coordinates.
A histogram plot of the binned values of one or more parameters is produced
using ps/histo. The number of bins can be specified using the qualifier
/bins=m. The default takes ten bins.
The /logarithmic qualifier bins the parameter logarithmically and
also displays it on a log scale. The /loga option is relevant only when
/histo is invoked.
The /cumulative qualifier gives a cumulative histogram.
It is possible to assign different symbols using the value or range of values
of a specified parameter. This is done with the /parm qualifier where
``parm" is replaced by the parameter name upon which the symbol selection is to
be made. For example, if the parameter is count rate, then
ps/count=(val1:val2, val3:val4,val5,val6,*)
The val1-val2 specifies a range of values for the first symbol, val3:val4
the second, val5 the third, and val6 the fourth (val can be either a
range or a single value). The * assigns all points to this symbol.
This qualifier can be used with all other ps options.
The sample, lightcurve, and spectral plots are made using the interactive
plotting and fitting package QDP/PLT. By specifying /plt as part of the
ps or pp commands, it will return the PLT> prompt after the plot has
finished. From this prompt, commands can be given to rescale the axes, change
the labels, create hardcopies using postscript files, and fit functions to the
data. These PLT commands are fully described in the ``QDP/PLT User's Guide"
or they can be listed on the terminal by typing ? or help.
A few commonly-used QDP/PLT commands are given here. It is recommended that
regular users become acquainted with the ``QDP/PLT User's Guide".
This produces a file with the extension .qdp which can be read back in
using the QDP program. QDP files are in ASCII and can be mailed over the
networks, and they provide a simple vehicle for data transport.
