The small size of handheld computers makes them conveniently mobile, but limits the amount of information that can be shown on their screens. This work introduces "peephole displays," an interaction metaphor in which the handheld computer is a movable window on a larger virtual workspace anchored to the userís physical reference frame. Peephole displays enable new forms of two-handed interaction for simultaneously navigating and manipulating information, including the ability to create and edit objects larger than the screen and the ability to drag and drop in three dimensions. I developed four iterations of the peephole hardware, and built and tested several peephole-augmented applications including a drawing program, a map viewer, and a calendar. A user study of 24 participants shows that the peephole technique can be more effective than current methods for navigating large information spaces on handheld computers.
Figure 1: Viewing a map. These images were made by blending two photographs taken from the same viewpoint. The position of the device is tracked and the display scrolls to produce the illusion of a movable view on a large street map floating in space. Notice how Gravier St., visible in both views, maintains a fixed position with respect to the outside world.
Figure 2: Note-taking on a large workspace. By using both hands together, a user can continue to write beyond the bounds of the screen.
Figure 3: Drawing on a large workspace. By using both hands together, a user can draw a figure larger than the screen in a single, natural stroke.
Figure 4: Viewing a calendar. Conventional PDA calendar programs have a day view, a week view, and a month view; the peephole calendar combines the strengths of all three into a single modeless view. This combined view is shown on the lower plane and an overview of the entire year is shown on an upper plane. The user can lift the display to switch to the year view and thereby navigate to a different month.
Figure 5: 3D drag-and-drop. The clipboard plane is located in space above the drawing plane. To transfer items to and from the clipboard, the user simply picks an item and lifts or lowers the display. Unlike conventional clipboards, this clipboard can contain more than one item and permits its contents to be viewed.