Introduction to Plotting Using ChIPS
[CIAO 3.4 Science Threads]
OverviewLast Update: 1 Dec 2006 - updated for CIAO 3.4: ChIPS version Synopsis: The Chandra Imaging and Plotting System (ChIPS) is the visualization interface which can receive commands from any application within CIAO. ChIPS is designed so that plots can be built up interactively in small steps and can easily be refined, saved, printed, and restored. It is particularly flexible at creating plots from tables, but also allows users to generate plots of selected columns from an image or event file. Related Links:
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Contents
- Getting Started
- Creating Simple Plots
- Customizing the Plot
- Plotting Two Datasets Together
- Plotting Two Datasets Separately
- Saving and Printing a Plot
- Getting More Help
- History
- Images
Getting Started
If you haven't obtained it yet, the data used in this thread is available as chips.tar.gz (SHIFT-click to download the file). Use the tar xvf chips.tar command to unpack the unzipped file.
Move to that directory and start a ChIPS session:
unix% chips Welcome to ChIPS, version CIAO 3.4 Copyright (C) 1999-2003, Smithsonian Astrophysical Observatory chips> ls data1.pha data2b.dat data4.tab plot.chp data2a.dat data3.tab data5.dat
Within ChIPS, Unix commands must be preceded by a dollar sign ($), except for cd, pwd, and ls. For example, to view the contents of the ASCII data data2a.dat:
chips> $more data2a.dat 40535 31.24 0.69 40872 29.67 0.36 41006 30.18 1.33 41285 30.5 0.3 41713 29.5 0.4 43556 26.2 0.1 . . (etc.) .
Also, ChIPS commands are case insensitive; they may be used in either upper or lower case.
Creating Simple Plots
To begin, we create a plot from the file data1.pha:
chips> plot data1.pha The inferred file type is PHA type I.
As seen in
Figure 1 , x is plotted from
the first column of the file, y from the second.
This can also be specified explicitly, e.g. for an ASCII file:
chips> clear chips> plot data2a.dat x 1 y 2
This selects column 1 as x and column 2 as y; see
Figure 2 .
The clear command is used to remove all
previous plotting objects and create a new blank drawing area.
If the file contains error data, they can be included:
chips> clear chips> plot data2a.dat 1 2 3
This command plots x and y from columns 1 and 2,
respectively, as shown in Figure
3 . Data from column 3 is used to plot symmetrical
error bars in y.
If the file contains data for nonsymmetrical error bars:
chips> clear chips> plot data3.tab x 1 y 2 yup 3 ydown 9
This command plots x and y from columns 1 and 2
respectively, as shown in Figure 4 ;
data from column 3 is used to plot the positive error bars in y and
data from column 9 is used to plot the negative error bars in y.
Customizing the Plot
Labels and titles may be added to a plot:
chips> clear chips> plot data1.pha chips> title "Test Plot" chips> ylabel "Count Rate" chips> xlabel "Channel"
In addition, the characteristics of the labels and title may be modified:
chips> xlabel blue chips> xlabel size 1.5 chips> ylabel blue chips> ylabel size 1.5 chips> title red
The plot now appears as shown in Figure
5 .
See the appropriate ahelp files for other commands that may be used to customize the appearance of the plot:
- axes: specify the bounding box surrounding a drawing area.
- curve: change curve attributes.
- errs: specify the appearance of errorbars.
- grids: add grid lines or change grid attributes.
- limits: set the ranges to be displayed in the axes.
- line: add a line or change line attributes.
- symbol: change or remove symbols from a curve.
- ticks: specify the spacing of tick marks.
- tickvals: control the numerical tick mark labels.
Plotting Two Datasets Together
An important ChIPS concept is the "plotting object". Plotting objects are curves, labels, lines, titles, etc. When multiple plotting objects of the same type exist in a single plot, each is assigned a unique reference number.
To plot two datasets in the same drawing area, the first curve is plotted:
then the second curve is added:
chips> plot data4.tab 1 2 3 chips> c 2 symbol square
When the symbol type for the second curve is changed, "c 2" specifies the curve on which you wish to operate.
Labels are then added to the drawing area:
chips> xlabel "Time (years)" chips> ylabel "Flux (2-10keV)" chips> xlabel size 1.5 chips> ylabel size 1.5
Figure 6 shows the resulting plot.
It may also be useful to overlay one dataset on another; here we plot a dataset overlayed by the fit:
chips> clear chips> plot data2a.dat 1 2 3 chips> plot data2b.dat chips> c 2 simpleline chips> c 2 symbol none chips> c 2 red chips> xlabel "Time (JD-2,400,000)" chips> ylabel Velocity
Figure 7 shows the resulting plot.
Plotting Two Datasets Separately
Similar to curves, multiple drawing areas may be created and referenced by a number.
Two drawing areas are created and a gap between them is defined:
chips> clear chips> split 2 chips> split gap 0.05
A curve is added to each drawing area:
Note that the "d #" portion of these commands specifies the drawing area.
Various modifications are made to the two drawing areas and their curves:
chips> d 1,2 symbol circle chips> d 1 tickvals x off chips> d 1 ylabel "Flux (2-10keV)" chips> d 2 xlabel "Time (years)" chips> d 2 ylabel "N_H (/10^{23} cm)" chips> d 2 xlabel size 1.5 chips> d all ylabel size 1.5
Both drawing areas are changed at the same time by using the
"d 1,2" or "d all" syntax. Figure 8 shows the resulting plot.
Add another curve to each of the drawing areas:
chips> d 1 plot data4.tab 1 2 3 chips> d 1 c 2 symbol square chips> d 2 plot data4.tab X 1 Y 4 yup 5 ydown 6 chips> d 2 c 2 symbol square chips> d 1 limits 1982.0 1999.0 0.5 3.5 chips> d 2 limits 1982.0 1999.0 0.0 4.5
Now it is necessary to give both the drawing area number
(d #) and the curve number (c #) to change
a curve attribute. Figure 9
shows the resulting plot.
Saving and Printing a Plot
The print command may be used to save a plot in postscript format or send it directly to the system printer:
chips> print postfile plot.ps chips> ls *ps plot.ps chips> print
The commands pagesize and colorsys are used to control the appearance of the hardcopy.
The store command may be used to save a plot for future use in another ChIPS session:
chips> store plot.chp chips> exit unix% chips Welcome to ChIPS, version CIAO 3.4 Copyright (C) 1999-2003, Smithsonian Astrophysical Observatory chips> restore plot.chp chips> exit
Getting More Help
There are several ways to get help on ChIPS:
- A complete discussion of each command can be brought up by typing ahelp from within ChIPS (e.g. "ahelp curve"). Use "q" to exit from the help page.
- This information is also available from the ChIPS Reference Manual.
- The chips help page contains information on how to use S-Lang within ChIPS.
History
14 Dec 2004 | reviewed for CIAO 3.2: no changes |
01 Dec 2005 | updated for CIAO 3.3: ChIPS version number |
01 Dec 2006 | updated for CIAO 3.4: ChIPS version |