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position data recognizable by the virtual world. However, the data
from the GPS is expressed in a geographical coordinate system,
whereas the virtual world uses Cartesian coordinate system, this
conversion may cause spatial and temporal inconsistency between
the mobile player and the desktop player. Additionally, because the
mobile player is moving in the physical world, the difference of these
two coordinate systems may further corrupt the causal order rela-
tionship of events within the shared virtual world. As a result, the last
concern is how to harmonize coordinates and events between these
two coordinate systems. The MSS uses the GPS time to synchronize
messages between the mobile player and itself. To the advanced state,
the grid approach to translate data between the two coordinate sys-
tems as discussed previously is implemented in MSS.
The following section will present a typical application of MiMAR
system—a network augmented reality campus in National Taipei University
(NTPU), Taiwan.
6.5 Three-Dimensional Virtual Campus
Other than the interaction issues discussed in the previous session, the
implementation approach will also affect the performance of the MiMAR
environment. The most straightforward implementation allows the mobile
device to communicate with the multiuser server directly and to implement
a proposed solution on the multiuser server. However, this type of imple-
mentation will overload the server and, then, decrease the performance of
the MiMAR environment. To avoid this problem, as illustrated in Figure 6.4,
a mediate server called a MSS was designed to realize the proposed solu-
tions. The MSS performs as a data mediator between the multiuser server
and the mobile player. For the multiuser server, MSS is a desktop player that
controls multiple avatars inside the virtual world. On the other hand, the
mobile player treats the MSS as a special purpose server that shares some of
its computation load.
The MSS is implemented on the Windows XP platform. To further verify
the validity of the proposed solutions, the MSS is realized in the existing net-
worked virtual environment called NTPU 3-D virtual campus [26]. The 3-D
virtual campus is a network virtual environment of National Taipei University
(NTPU), Taiwan. By adding MSS, both the mobile players and desktop players
are allowed to join this 3-D campus environment. The position of the mobile
player is derived by the GPS receiver. The mobile device (i.e., a wearable com-
puter or a notebook) will translate and transmit its received GPS data to the
server. The server then will forward the received data to other players for
