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: http://www.stsci.edu/hst/training/events/IDLTopics/SSD98IDL/IDL_plotting1.html
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IDL can use any one of the following three plotting coordinate systems.
Data | The coordinate system established by your data when you use a Plot, Contour, or Surface command. This is the default coordinate system for most of the IDL graphics commands. |
Device | The physical coordiante system of the graphics device. It ranges from 0 to the number of addressable rows and columns on the graphics display. Device coordinates are usually thought of as pixels. This is the default for the TV and TVScl commands. |
Normal | The normalized coordinate system. It ranges from 0 to 1 in the plot window. |
xyouts, x, y, 'Sin(s)', /normal
cursor, x, y, /device
To general a line plot, one would use the plot procedure. The plot procedure can
take one or two arguments. IDL will try to create the best plot with the information
at hand, and it will automatically scale the plotting ranges. For example:
IDL> num = findgen(40)*10
IDL> line=sin(num*!DtoR)
IDL> plot, line
IDL will generate a plot using the x indices as the independent variable index, and
the values in x as the dependent values.
You can provide a second argument to the plot command.
IDL> plot, num, line
To customize your plots, you can use the keywords associated with the plot procedure
(you can find more about the keywords from the online help browser). Here are a few
things you can do:
For example, if you want to use a different symbol:
IDL> plot, num, line, psym = 1
You can choose a different line style by using the LineStyle keyword.
IDL> plot, num, line, linestyle = 1
The table below summarizes the different type of line styles.
Value |
Line Style |
0 |
Solid |
1 |
Dotted |
2 |
Dashed |
3 |
Dash Dot |
4 |
Dash Dot Dot |
5 |
Long Dash |
You can also change the line thickness by using the Thick keyword.
IDL> plot, num, line, linestyle=2, thick=3
You can choose a different plotting symbol by using the PSym keyword.
IDL> plot, num, line, psym=1
The table below summarizes the different type of symbols.
Value |
Symbol |
0 |
No Symbol. Points are connected with solid lines. |
1 |
Plus sign |
2 |
Asterisk |
3 |
Period |
4 |
Diamond |
5 |
Triangle |
6 |
Square |
7 |
X |
8 |
User defined (with the UserSym procedure) |
9 |
Undefined |
10 |
Data is ploted in histogram mode. |
-Psym |
Negative values connect symbols with lines. |
Using a negative value for the psym keyword will connect your symbols with lines.
IDL> plot, num, line, psym=-1
This will connect the plus signs with lines.
You can use the UserSym procedure to create your own symbol. The symbol
you created can be used by setting the psym keyword to 8. Here is an example
that creates a circle. The following steps first generate the data points for the
circle, and then the usersym procedure is called to create the circle symbol.
IDL> n = 17.0 ; the circle will be "created" with 17 data points (vertices)
IDL> theta = findgen(n)/(n-1.0)*360.0*!DtoR ;
IDL> x = 1.0*sin(theta)
IDL> y = 1.0*cos(theta)
IDL> usersym, x, y
So now you can use the circle symbol by:
IDL> plot, num, line, psym = 8
Finally, you can change the size of the symbol by using the SymSize keyword:
IDL> plot, num, line, psym = 8, symsize = 2.0
When you look at the online help, you will notice that there are many keywords associated
with the plot command. The table below lists a selected few to illustrate what you
can used to annotate your plots. You should try to experiment with the various keywords
available for the plot procedure.
CharSize | The overall character size for the annotation. The character sizes for the different
axes are scaled from this value. The main title is scaled to 1.25 times this size.
A CharSize of 1.0 is normal size. IDL> plot, num, line, charsize=2.0, title='GHRS spectrum |
[XYZ]CharSize | The character sizes for the annotation on the individual axes. The value of this
keyword is used to scale the value set by the keyword CharSize. IDL> plot, num, line, charsize=2.0, xcharsize=0.8, xtitle='wavelength' |
Title | Places a title above the plot. IDL> plot, num, line, title='GHRS spectrum' |
[XYZ]Title | The title for each individual axis. IDL> plot, num, line, xtitle='wavelength' |
SubTitle | Place a subtitle underneath the X axis. |
[XYZ]TickName | A string array of up to 30 elements containing the labels for major tick marks. |
Using what you have learned here, try to modify your plot of the GHRS spectrum. Also,
try to incorporate the changes into your plotting program.