the virtual and physical models and
cause the projections to “spill over.”
While a tangible 3D tabletop does
not have to be a multi-user installation,
it is straightfor ward to develop it so
that it can be; the three installations
presented here all support multiple
users. This leads to the question of how
the interface supports and hinders
certain types of collaboration. While
users may interact individually with
Tangible Urban Planning, for instance,
all operations are made visible to
other users, and many of the potential
interactions with the tangibles affect
the rest of the system. It can be seen as
an inherently collaborative installation,
in that every action potentially affects
everyone else using it. For instance, if
one user is manipulating the position
of the sun and time of day, it will affect
other users who are simultaneously
exploring the position and appearance
of buildings. While this may be
preferable in some situations—for
example, when a group of citizens
discuss the systemic effects of urban
planning initiatives with architects and
policy makers at a public hearing—it
will hinder other types of work—for
example, when architects jointly discuss
a master plan and subsequently work
individually on specific components of
This leads us to consider the typeand complexity of information forwhich this interface is suited. Broadlyspeaking, present single-user devicesare generally better suited for handlingcomplex content and interaction,whereas shared devices often presentsimpler or more abstract content andallow for more basic forms of interactionand manipulation. For example, when itcomes to image manipulation, single-user software such as Photoshop is ahighly sophisticated tool that enablesexpert users to carry out compleximage manipulation, whereas mostexamples of large-scale multi-userinstallations typically support onlyvery basic image manipulation, such asresizing and adding predefined filters.
While the three installations presented
for the Lego World 2013 event. It was
designed to showcase Lego in a multi-
user walk-up-and-use installation, and
was the first example of a tangible 3D
tabletop installation put to use outside
research labs [ 10]. The installation
made use of two forms of tangibles,
quadratic cubes and stylized buildings,
both constructed from Lego brick
(Figure 5 and [ 11]). Users could fill
the cubes with colors, then paint the
buildings and push and rearrange
virtual bricks displayed on the table.
In addition, a couple of “Easter eggs”were implemented for special events;for example, when a building wasfully painted in different colors, itemitted a strong pulse that repelled thesurrounding virtual bricks. The noveltyof 3D projection itself was intendedto pique the curiosity of onlookersand users and invite them to explorethe relations between tangibles andtabletop content.
The most intriguing potential oftangible 3D tabletops from aninteraction research perspective isarguably that all physical objectsin the system can become interfacecomponents, and that they cansimultaneously be input and outputdevices. A tangible 3D tabletop can becharacterized as a particular type ofaugmented reality. However, it offers anadvantage over most other augmentedreality systems in that digital contentis projected immediately onto thephysical objects, rather than requiringa mediating device such as a mobilephone or a head-mounted display toadd extra layers of information to thephysical surroundings. By nature itis also a less flexible interface; first,because it requires a tabletop and aset of carefully calibrated projectors;second, because all the physical objectsmust be modeled in the system beforethey can be employed. For example, inthe case of Projected Play, users couldnot reconfigure the Lego buildings byadding or removing bricks, since thiswould create an incongruence between
A tangible 3D tabletop can be
characterized as a particular type of
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