emitter and an optically isolated IR light detector, allowing it to emit light and to
detect the intensity of incident light at the same time) placed behind an LCD panel.
When a reflective object is placed in front of the panel, a part of the light is reflected
back and detected by the optosensor. The data generated by the sensor gr id is a low-
resolution grayscale “image” that can be processed to extract information about the
number of contact points and their position. N-trig uses a capacitive sensing system
(i.e., signals are emitted that capacitively couple with users when they touch the sur-
face) mounted in front of the LCD panel to detect touch, and a speci alized sensor to
detect and track the stylus.
A tangible user interface (TUI), initially termed a graspable user interface [22], as
shown in Figure 1.5, is one that integrates both the representation and the control
of computation in the same physical artifact. It helps provide physical form to
computational artifacts and digital information, and, unlike a GUI, it ...makes
information directly graspable and manipulable with haptic feedback”[21]. The
informal definition of a touch screen given in Section 1.2 can be made more rigorous
and broad when defined as a “surface user interface” (SUI), which relies on a self-illu-
minated (e.g., LCD) or projected horizontal or vertical interactive surface coupled
with computation control on the same physical surface. As with a TUI, the outputs
from and inputs to a SUI are tightly coupled. SUI-based touch screens range from
small personal devices such as the iPhone to large public interactive surfaces such
as the DiamondTouch.
SUIs are used in public places (kiosks, ATMs) or in small personal devices (PDAs,
iPhones) where a separate keyboard and mouse cannot or should not be used. Basic
SUIs have been common for over 20 years in the form of interact ive kiosks, ATMs,
and point-of-sale systems, which rely on touch-screen technology with simple button
interfaces. The basic technologies in many products, such as the Nintendo DS with
Tangible UI
Graphical UI
Window Icon Menu Handle Control
Phicon Tray Phandle Instrument
TUI instantiations of GUI elements [21]. Courtesy Brygg Ullmer.
10 CHAPTER 1 Face-to-Face Collaborative Interfaces

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