width 2 from the North to the South Pole. If the line
segments are short enough, we can use them to
create curves, but because all line segments are
drawn subsequently, if many poly-lines should be
drawn, it needs more time.
3 INTERACTIVITY
All approaches described in Section 2.1 enable to
select any clip from the prepared datasets and view
it. Moreover, edutainers can use tablet to zoom to
some place on the globe or to draw simple on the
actually viewed dataset, to show some interesting
details. But there is no way how to interact with the
sphere more, or how to enable children to join any
game that will test their knowledge about the Earth,
planets or any other interesting topic. Our first aim
was to add to the SOS system a new feature which
would enable visitors of the science centre to affect
somehow what they see, to select any place and to
get more information and to learn more simply by
“clicking” on the sphere.
Because the SOS does not offer any tool, how to
impulse it and to launch any action we had to search
for another solution. SOS server is running online
and is able to react immediately on the command
sent via the telnet connection. It is the only way how
to give SOS real time instruction about what
operation should be provided. We have decided to
create an external application that would get
impulses from the user (via GUI or any special
hardware) and at the same time it would send
commands for the SOS directly to the SOS server
over the telnet connection.
As additive hardware we have selected Nintendo
Wii Remotes, because several pieces were already
bought with the SOS system. As mentioned in
Section 2.1, they have originally just very limited
control function. And because they were not used at
all, we were asked to upgrade their function. For the
communication between computer and Nintendo Wii
Remote the bluetooth wireless technology is used.
3.1 Interactive Features Concept
We need to implement two basic features so that any
game or interactive application could be built on the
SOS interactive module – clicking cursor (or
multiple cursors) and places/areas determination.
The first feature is the cursor. A tool that would
move on the globe and by clicking would run any
actions. Moreover, if we want to use the system for
any game, where more users would compete, we
need to place more cursors on the globe and to
control them separately and so we should extend the
system for multiple cursors.
To select and mark interesting places or areas,
we need to create any tool that would be able to
border any selected area on the globe. Moreover,
these areas should be clickable. It means that if the
user will use the click action, the area placed on the
position of the cursor will be able run the action. So
we need a way to describe a continuous border, an
algorithm to decide if the point (position of the
cursor) is inside the border and some mechanism to
show the area on the globe. Moreover, it would be
useful so that the area could be marked as active, if
the cursor is moving over the sphere (it means, if the
cursor moves over the area, it changes its border
colour and if the cursor leaves the area, border
colour is changed back as the non-active area). To
describe the border, it is sufficient to keep
coordinates of poly-line vertices together with the
name of the area. Coordinates can be used as for the
border visualization and so for the inside decision
algorithm. The detection algorithm works in two
levels. Each area has its bounding box, and before
exact test, if the point lies in the area, the bounding
box test is provided. When it is positive, the ray-
crossing algorithm based on the Jordan Curve
Theorem (Schneider and Eberly, 2002) is used to
determine exactly, if the point (position of the
cursor) lies inside the polygon (tested area).
3.2 SOS Control Module
We have designed a module covering all the SOS
control functions, telnet connection operations and
also supporting functions for data preparation. This
section describes approaches of using SOS abilities
for the interactive use. The following subsections
show an example of the model usage that was
further developed and implemented into the form of
complete workable system transferred into the real
use (see Section 4). Also some facts about the real
implementation of the model and reasons for
technologies selecting are given (Section 3.3). The
main idea of module integration and example of the
module usage in the interactive educational game
can be seen in Figure 4. The game server (created on
the basis of the interactive module) is connected to
the SOS server and ensures the automation
commands processing. To the game server we can
connect several Wii gamepads, each can control its
own cursor and so the game server has to process the
commands from various sources. The client
application ensures the comfortable game selection,
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