Biomedical Engineering Reference
In-Depth Information
Fig. 7.11
The eMagin z800 helmet contains a three axis rotation sensor
accelerometers cannot tell the system the height above the ground or distance from
any local feature without other calibration. Calibrating against GPS fixes is prob-
lematic because those fixes are inaccurate and the civilian implementations include
a moving offset by design. Thus currently, outside of the lab, mobile augmented
reality is limited to display modes that use gross position referencing, such as labels
over whole buildings, rather than being able to accurate align an object to some-
thing the size of a window or door. Researchers that are prepared to integrate more
equipment than can be found on current smartphones can build systems that maintain
good registration, but the vision of being able to walk around and see an augmented
real environment where the augmentations are seamlessly integrated is still a few
years off.
The other common use for pose & movement sensors is for head-mounted displays
and handheld devices. Some consumer HMDs include a two-DoF or three-DoF rota-
tion tracker so that the user can rotate her head to directly control the orientation
of the viewpoint (Fig. 7.11 ). These sensors do not track linear acceleration, so they
cannot provide motion parallax, thus in the lab these sensors are usually integrated
with a position tracking technology as well. Recent game controller devices such as
the Nintendo Wii Remote and Sony Move controllers integrate accelerometers and
gyroscopes. Again, these two controller technologies can only tell the console about
local rotation of the device. This is insufficient to do position tracking of the tech-
nology, so it can't, on its own, support pointing at the screen. Both provide separate
position tracking for this.
The basic component sensors thus form an important part of more sophisticated
trackers. For example, the InterSense IS900, which is a current state of the art position
tracker that is commonly used in virtual reality laboratories, includes an accelerom-
eter as a component. Accelerometers in combination can create more sophisticated
models of moving objects. The XSens system is a motion capture technology where
 
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