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## 2D line annotation objects

Figure 17

2D line annotation objects, shown in figure, are created by clicking the 2D Line button in the Create new area on the Objects tab. 2D line annotation objects are simple line objects that are drawn on top of plots in the visualization window and are useful for pointing to features of interest in a visualization. 2D line annotation objects can be placed anywhere in the visualization window and you can set their locations, arrow properties, and color.

2D line annotations are described mainly by two coordinates that specify the start and end points for the line. The start and end coordinates are specified as pairs of floating point numbers in the range [0,1] where the point (0,0) corresponds to the lower left corner of the visualization window and the point (1,1) corresponds to the upper right corner of the visualization window. You can set the start or end points for the 2D line annotation by entering new start or end points into the Start or End text fields in the 2D line object interface. You can also click the down arrow to the right of the Start or End text fields to interactively choose new coordinates using the screen positioning control.

Figure 18

Once the 2D line annotation has been positioned there are other attributes that can be set to improve its appearance. First of all, if the 2D line annotation is being used to point at important features in a visualization, you might want to increase the 2D line annotation's width to make it stand out more. To change the width, type a new number of pixels into the Width spin box or use the +/- buttons to increment or decrement the current width. After changing the width, the color of the 2D line annotation should be chosen to stand out against the plots in the visualization. The color that you use should be chosen such that the line contrasts sharply with the plots over which it is drawn. To choose a new color for the line, click on the Line color button and choose a new color from the Popup color menu. You can also adjust the opacity of the line by using the opacity slider next to the Line color button.

Figure 19

The last properties that are commonly set for 2D line annotations determine whether the end points of the line have arrow heads. The 2D line annotation supports two different styles of arrow heads: filled and lines. To make your line have arrow heads at the start or the end, make new selections from the Begin Arrow and End Arrow menus.