Trace

This command turns tracing on or off for each selected object. If all the selected objects are currently being traced, a check mark appears next to the command. Choosing the command turns tracing off for each selected object. If no check mark appears, choosing the command turns tracing on for each selected object.

The keyboard shortcut for Trace is Ctrl+T (Windows) or z+T (Mac).

When an object is traced, it leaves behind a trail as it moves, no matter how the motion is caused—whether by dragging the traced object, by dragging some object on which the traced object depends, or by animating.

Tracing can be useful for exploring how an object’s movement is constrained or for creating interesting mathematical art.

The faster a traced object moves, the more spread out its trail; the slower the object moves, the denser its trail.

You can use Color Preferences to make traces gradually fade over time and eventually disappear. You can also control how fast traces fade—or turn off the fading of traces altogether. If fading is disabled, traces will remain on the screen indefinitely. To remove traces (whether fading or not) from the screen, choose Erase Traces from the Display menu.

Think of a trace as a temporary display of an object’s locus. To construct a permanent locus, use the Locus command from the Construct menu.

There’s an important difference between erasing traces and deactivating tracing for an object or objects. Erasing traces (using the Erase Traces command) removes all existing traces from the screen but has no effect on whether objects will leave traces in the future. Turning tracing off for an object (using the Trace command) prevents that object from leaving traces as it moves in the future, but has no effect on any traces the object has already left on the screen. If you want to remove all existing traces an object has left behind, and also to prevent that object from leaving traces in the future, you must use both commands:

1. Select the object and choose the Trace command to turn off future tracing for the object.

The perpendicular bisector of a segment attached to a circle is selected and traced (left). As the segment’s endpoint is dragged around the circle, the bisector traces a hyperbolic envelope (center). Animating the endpoint around the circle results in smoother traces (right).