Arc by Points Tool Operation

As the Arc by Points tool has several keypresses which can add or change its functionality, we strongly suggest installing the free Astute Graphics plugin Astute Buddy, which creates a panel that dynamically updates to inform you of the various keys which can be pressed in the tool’s current context.

The Arc by Points tool is used by first specifying the two endpoints of the arc, and then adjusting the arc through these points. The first step can be done either by clicking on the first point and then dragging to the second, or by clicking on each point; the latter method has the advantage of allowing you to scroll, zoom, change the view mode, etc. in the middle of the operation. Shift may be held to constrain the angle between the endpoints.

There are two methods of adjusting the arc through the initial two points by creating a third point. Which method is initially in force depends on the tool preference Third Point Indicates Direction. By default, this preference is off and the arc is adjusted such that it passes through the third point, which is created by clicking on the artboard. When moving the cursor to locate the third point, the arc and its current radius are previewed using annotations.

Arc by Points Tool Example

When the Third Point Indicates Direction preference is turned on, the third point is used to specify the initial tangent angle of the arc at one of its end points.

Arc by Points Tool - Third Point Indicates Direction

When locating the third point using Third Point Indicates Direction, the Shift key can be pressed to constrain the direction of the direction line, and the Option/Alt key can be pressed to change the endpoint from which the line is drawn.

Using either method, as the third point approaches a spot exactly in line with the start and end points (but not in between them), the arc will become too large to create; a text annotation by the cursor indicates this.

The Third Point Indicates Direction preference can be toggled while creating the arc by pressing the key assigned to “Increase Diameter” in the native Keyboard Shortcuts dialog (by default, for English-speaking locales, the right bracket key "]").

When dragging to locate the third point (mouse button down), two additional keypresses can be used:

• Command/Ctrl: Toggles Slow-Drag mode, in which the cursor is “geared down” by a factor specified in the tool preferences for finer control over the arc’s creation.

• J: Toggles the Automatically Join to Existing Paths preference (see Arc by Points: Preferences).