Game Development Reference
In-Depth Information
Three-Dimensional Input Devices
A three-dimensional device delivers three data values simultaneously. Such devices
are rare but are becoming more common as the game industry begins to adopt
motion-sensing devices like the Wii Remote.
ACCELEROMETERS
An accelerometer is not a switch or button that the player directly manipulates. It is
an electronic device that measures the rate of acceleration it experiences. Game
hardware manufacturers build accelerometers into controllers such as the Wii
Remote so the player can wave the controller around rather than simply hold it and
press buttons. With the data from multiple accelerometers, you can compute how
far and how fast the player moves the remote, and in what direction. The Nintendo
Wii Remote and Nunchuck, and the Apple iPhone, are the best-known devices that
use accelerometers in gaming.
NOTE
Some devices
built for non-gaming
applications need to
measure acceleration
in only one or two
dimensions, so they
contain simpler accel-
erometers. However,
motion-sensitive gam-
ing devices routinely
use accelerometers
capable of measuring
acceleration in all
three spatial dimen-
sions so they can
detect movement in
every direction. They
provide three accelera-
tion data at a time.
When an accelerometer is at rest with respect to the Earth (sitting still on a table,
for example), it reports the force of gravity. This means that you can also use an
accelerometer as a tilt sensor. If the acceleration of gravity appears to change direc-
tion, it means the device has been tilted with respect to the ground. You can also
detect if the player has turned it upside down: The direction of the acceleration of
gravity will be reversed.
An accelerometer returns absolute acceleration information. If it were in zero grav-
ity and undergoing no acceleration, it would return zero in all three dimensions.
GLOBAL POSITIONING SYSTEMS
Global positioning systems have become commonplace in high-end mobile phones,
and it won't be long before they are ubiquitous in phones, personal digital assis-
tants (PDAs), and handheld gaming devices. A GPS returns the device's latitude and
longitude on the surface of the Earth, as well as the altitude above sea level. The
player uses a GPS as input to a game by moving the GPS around in the environ-
ment. The UK-based art collective Blast Theory has constructed several augmented
reality games that use global positioning systems. Players travel around a cityscape
on foot, carrying a GPS-enabled device that helps them play the game.
GPS devices return absolute positional information. By taking measurements over
time, you can use this data to compute the player's speed and direction.
GPS devices have two significant drawbacks at the moment. First, because they
need to receive data from satellites orbiting the Earth, they only work in areas
where they can easily receive the satellites' transmissions—usually outdoors.
Second, the current generation of GPS technology is only accurate to within
several meters, so they're only useful on a large scale. The European Galileo satel-
lite navigation system, which is due to come online in 2013, is designed to be
accurate to the 1-meter range.
