Appendix D: Overview of PLT
XSPEC uses the PLT library, which is in turn based on
PGPLOTD.1,
to implement its plotting capabilities.
Extensive documentation for the PLT graphics routine is available in
the QDP/PLT Users's Guide
and from PLT's interactive help. This
appendix is intended to provide information to assist in using PLT
from within the XSPEC program.
Within XSPEC, it is possible to set your graphics device using the cpd
command. Any PGPLOT device supported by your local version of PGPLOT
is accepted. The cpd command can also be used to display a list of all
PGPLOT devices. If you fail to enter a device name, you will be
prompted for a PGPLOT device every time you generate a new plot.
From XSPEC, there are two ways to call the PLT routine. Both have the
same syntax which is described in the corresponding manual section.
The plot <plot mode> command will produce a graph and
control will return immediately to XSPEC.
The iplot <plot mode> command will put XSPEC into
interactive plot mode. The prompt
PLT>
will appear after XSPEC has finished producing the graph. At this point, you
can enter PLT commands to inspect interesting parts of the graph, add
labels, or make a hardcopy file for later printing.
Getting started with PLT
In the following description of PLT commands, the full
command is described. Capital letters denote the shortest abbreviation
of the command that will be recognized. Here is a brief guide to some
of the PLT commands that can be entered when iplot is invoked.
- HElp will provide you with descriptions of the PLT commands.
- Plot redraws the display using all of the commands that change
the graph entered since the last plot.
- Rescale followed by two numbers, will set the minimum and
maximum of the plotted x-range to the numbers specified. Without
further arguments, Rescale X or Rescale Y will reset the
minimum and maximum values to their default values. Rescale also
updates the screen immediately. Other commands allow you to make
several changes to the the graph without having to wait for the
screen to be updated after every change.
- LAbel <Top,X,Y> [<string>] adds labels to
various locations on the graph. For example, typing LA Top EXOSAT
was great will cause the message “EXOSAT was great” to appear at the
top of the graph the next time the display is redrawn. Without the
string argument the current label for Top, X, or Y is set to the
empty string.
- Hardcopy [?, PGPLOT plot device] creates a file that
can later be printed. Since it redraws the graph and sends it to a
file, it does not reproduce what currently is visible on the
graphics display, but rather what you would see if you re-issued the
Plot command. With the optional “?” argument, Hardcopy returns the
current hardcopy plotting device. This can be overridden with
Hardcopy [PGPLOT device name].
- WData writes a QDP data file to disk. The wdata output file depends on
how complicated the plot is (ie. multiple spectra, models, etc.); for the standard
case of "plot data" with 1 spectrum and a fitted model, 5 columns of data are given:
- col 1: x-axis value (same for both spectrum and model, in either channel energy or wavelength units depending on the plot)
- col 2: x-axis error. Half of the bin-width, in either channel, energy, or wavelength units
- col 3: y-axis value for the spectral data point
- col 4: y-axis error for spectral data point (the +/- length of the error bars)
- col 5: y-axis value for the model
Since the models aren't plotted with y-axis errors, there is no col 6
for the model error. If plotting of additive components had been
turned on then there would be one additional column for each additive
component. If there are multiple spectra plotted then they are
separated in the output file by a line of NOs with one NO for each column.
- EXit returns control to XSPEC. Any changes you have made
to the plot will be lost.
PLT Command summary
CLear |
Immediately clear the graphics device |
COlor |
Change the default colour index |
CONtour |
Produce a contour plot |
CPD |
Change the plotting device |
CQuit |
Clear the graphics device and return control to XSPEC |
CSize |
Change the default character size |
Error |
Control whether errors are displayed and used in fitting |
EXit |
Exit PLT and return control to XSPEC |
Fit |
Fit the PLT model to the data |
FNy |
Evaluate the model at the specified location |
FOnt |
Change the default text font |
Freeze |
Freeze a parameter value |
GAp |
Change the default gap size between the data and the edge |
Grid |
Control the location of the major and minor tic marks |
Hardcopy |
Make a file that can later be printed |
HElp |
Obtain help on any PLT command |
Imodel |
Numerically integrate the model over specified range |
LAbel |
Add or remove labels from the plot |
LIne |
Control whether a line is used to connect data points |
LOg |
Control whether data is plotted using a log10 scale |
LStyle |
Change the default style of the line connecting the data
points |
LWidth |
Change the default line width |
MArker |
Control whether the data points are plotted with markers |
MOdel |
Define a PLT model |
Newpar |
Change a parameter value associated with the model |
PLot |
Immediately re-plot the data |
PRompt |
Change the PLT prompt |
Rescale |
Reset the minimum and maximum plot range |
SCr |
Change the color representation of the specified color index |
SHow |
Display the values of PLT internal variables |
SKip |
Control how PLT divides data into vectors |
STatistics |
Compute various statistical properties of the data |
THaw |
Allow a parameter value to vary during a fit |
Time |
Control whether the time stamp is plotted |
Uncertainty |
Compute the uncertainty in a parameter value |
VErsion |
Display date of the most recent modification to PLT |
Viewport |
Control the size of the viewport plotting area |
WData |
Write a QDP data file to disk |
WEnviron |
Write both QDP data and header files to disk |
WHead |
Write a QDP header file to disk |
WModel |
Write a model file to disk |
Xaxis |
Define the method used to calculate the x-variable |
Yaxis |
Define the y-axis scale for a contour plot |
$ |
Execute operating system commands |
@filename |
Read commands from a PLT command (.pco) file |
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