Plotting Keyword Parameters

The IDL plotting procedures are designed to produce acceptable results for most applications with a minimum amount of effort. The large number of keyword parameters, described in the IDL Reference Guide, in combination with plotting and graphic system variables, allow users to customize the graphics produced by IDL. Most of these keyword parameters pertain to advanced programming. The major keyword parameters are described and illustrated by example in this section.

Correspondence with System Variables

Many of the keyword parameters correspond directly to fields in the system variables !P, !X, !Y, or !Z. When specifying a keyword parameter name and value in a call that value affects only the current call, the corresponding system-variable field is not changed. Changing the value of a system-variable field changes the default for that particular parameter and remains in effect until explicitly changed. The system variables involving graphics and their corresponding keywords are detailed in System Variables.

Example-The COLOR Keyword Parameter

The keyword parameter COLOR corresponds to the field COLOR of the system-variable structure !P and is referenced as !P.COLOR. To set the color of a plot to color-index 12, use the following statement:

PLOT, X, Y, COLOR = 12 

Future plots are not affected and are drawn with color index !P.COLOR, which is normally set to the number of available colors minus one.

The interpretation of the color index varies among the devices supported by IDL. With color video displays, this index selects a color (normally a red, green, blue (RGB) triple stored in a device table). You can control the color selected by each color index with the TVLCT procedure which loads the device color tables.

Other devices have a fixed color associated with each color index. With plotters, for example, the correspondence between colors and color index is established by the order of the pens in the carousel.

To change the default color of future plots, use a statement such as:

!P.COLOR = 12 

which sets the default color to color-index 12. You can override this default at any time by including the COLOR keyword in the graphic routine call.