<s>
In	O
virtual	B-Application
reality	I-Application
(	O
VR	O
)	O
and	O
augmented	B-General_Concept
reality	I-General_Concept
(	O
AR	O
)	O
,	O
a	O
pose	B-Operating_System
tracking	I-Operating_System
system	O
detects	O
the	O
precise	O
pose	B-Architecture
of	O
head-mounted	B-General_Concept
displays	I-General_Concept
,	O
controllers	O
,	O
other	O
objects	O
or	O
body	O
parts	O
within	O
Euclidean	O
space	O
.	O
</s>
<s>
Pose	B-Operating_System
tracking	I-Operating_System
is	O
often	O
referred	O
to	O
as	O
6DOF	O
tracking	O
,	O
for	O
the	O
six	O
degrees	O
of	O
freedom	O
in	O
which	O
the	O
pose	B-Architecture
is	O
often	O
tracked	O
.	O
</s>
<s>
Pose	B-Operating_System
tracking	I-Operating_System
is	O
sometimes	O
referred	O
to	O
as	O
positional	B-Operating_System
tracking	I-Operating_System
,	O
but	O
the	O
two	O
are	O
separate	O
.	O
</s>
<s>
Pose	B-Operating_System
tracking	I-Operating_System
is	O
different	O
from	O
positional	B-Operating_System
tracking	I-Operating_System
because	O
pose	B-Operating_System
tracking	I-Operating_System
includes	O
orientation	O
whereas	O
and	O
positional	B-Operating_System
tracking	I-Operating_System
does	O
not	O
.	O
</s>
<s>
In	O
some	O
consumer	O
GPS	O
systems	O
,	O
orientation	O
data	O
is	O
added	O
additionally	O
using	O
magnetometers	O
,	O
which	O
give	O
partial	O
orientation	O
information	O
,	O
but	O
not	O
the	O
full	O
orientation	O
that	O
pose	B-Operating_System
tracking	I-Operating_System
provides	O
.	O
</s>
<s>
In	O
VR	O
,	O
it	O
is	O
paramount	O
that	O
pose	B-Operating_System
tracking	I-Operating_System
is	O
both	O
accurate	O
and	O
precise	O
so	O
as	O
not	O
to	O
break	O
the	O
illusion	O
of	O
a	O
being	O
in	O
virtual	O
world	O
.	O
</s>
<s>
Many	O
interfaces	O
have	O
also	O
been	O
designed	O
to	O
monitor	O
and	O
control	O
one	O
's	O
movement	O
within	O
and	O
interaction	O
with	O
the	O
virtual	O
3D	O
space	O
;	O
such	O
interfaces	O
must	O
work	O
closely	O
with	O
positional	B-Operating_System
tracking	I-Operating_System
systems	O
to	O
provide	O
a	O
seamless	O
user	O
experience	O
.	O
</s>
<s>
Another	O
type	O
of	O
pose	B-Operating_System
tracking	I-Operating_System
used	O
more	O
often	O
in	O
newer	O
systems	O
is	O
referred	O
to	O
as	O
inside-out	O
tracking	O
,	O
including	O
Simultaneous	B-Application
localization	I-Application
and	I-Application
mapping	I-Application
(	O
SLAM	B-Application
)	O
or	O
Visual-intertial	O
odometry	O
(	O
VIO	O
)	O
.	O
</s>
<s>
One	O
example	O
of	O
a	O
device	O
that	O
uses	O
inside-out	O
pose	B-Operating_System
tracking	I-Operating_System
is	O
the	O
Oculus	B-General_Concept
Quest	I-General_Concept
2	I-General_Concept
.	O
</s>
<s>
Sometimes	O
referred	O
to	O
as	O
indoor	B-Device
GPS	I-Device
.	O
</s>
<s>
The	O
tags	O
triangulate	B-Algorithm
their	O
3D	O
position	O
using	O
the	O
anchors	O
placed	O
around	O
the	O
perimeter	O
.	O
</s>
<s>
A	O
wireless	O
technology	O
called	O
Ultra	O
Wideband	O
has	O
enabled	O
the	O
position	B-Operating_System
tracking	I-Operating_System
to	O
reach	O
a	O
precision	O
of	O
under	O
100	O
mm	O
.	O
</s>
<s>
Optical	O
tracking	O
uses	O
cameras	O
placed	O
on	O
or	O
around	O
the	O
headset	O
to	O
determine	O
position	O
and	O
orientation	O
based	O
on	O
computer	B-Application
vision	I-Application
algorithms	I-Application
.	O
</s>
<s>
This	O
method	O
is	O
based	O
on	O
the	O
same	O
principle	O
as	O
stereoscopic	B-Algorithm
human	I-Algorithm
vision	I-Algorithm
.	O
</s>
<s>
Tracking	O
with	O
markers	O
involves	O
targets	O
with	O
known	O
patterns	O
to	O
serve	O
as	O
reference	O
points	O
,	O
and	O
cameras	O
constantly	O
seek	O
these	O
markers	O
and	O
then	O
use	O
various	O
algorithms	O
(	O
for	O
example	O
,	O
POSIT	B-General_Concept
algorithm	I-General_Concept
)	O
to	O
extract	O
the	O
position	O
of	O
the	O
object	O
.	O
</s>
<s>
In	O
this	O
method	O
,	O
cameras	O
are	O
placed	O
in	O
stationary	O
locations	O
in	O
the	O
environment	O
to	O
track	O
the	O
position	O
of	O
markers	O
on	O
the	O
tracked	O
device	O
,	O
such	O
as	O
a	O
head	B-General_Concept
mounted	I-General_Concept
display	I-General_Concept
or	O
controllers	O
.	O
</s>
<s>
The	O
original	O
Oculus	B-Device
Rift	I-Device
utilizes	O
this	O
technique	O
,	O
placing	O
a	O
constellation	O
of	O
IR	O
LEDs	O
on	O
its	O
headset	O
and	O
controllers	O
to	O
allow	O
external	O
cameras	O
in	O
the	O
environment	O
to	O
read	O
their	O
positions	O
.	O
</s>
<s>
This	O
method	O
is	O
the	O
most	O
mature	O
,	O
having	O
applications	O
not	O
only	O
in	O
VR	O
but	O
also	O
in	O
motion	B-Application
capture	I-Application
technology	O
for	O
film	O
.	O
</s>
<s>
It	O
uses	O
cameras	O
on	O
the	O
headset	O
for	O
a	O
process	O
called	O
SLAM	B-Application
,	O
or	O
simultaneous	B-Application
localization	I-Application
and	I-Application
mapping	I-Application
,	O
where	O
a	O
3D	O
map	O
of	O
the	O
environment	O
is	O
generated	O
in	O
real	O
time	O
.	O
</s>
<s>
This	O
tech	O
allows	O
high-end	O
headsets	O
like	O
the	O
Microsoft	B-General_Concept
HoloLens	I-General_Concept
to	O
be	O
self-contained	O
,	O
but	O
it	O
also	O
opens	O
the	O
door	O
for	O
cheaper	O
mobile	O
headsets	O
without	O
the	O
need	O
of	O
tethering	O
to	O
external	O
computers	O
or	O
sensors	O
.	O
</s>
<s>
Inertial	O
tracking	O
use	O
data	O
from	O
accelerometers	O
and	O
gyroscopes	B-Application
,	O
and	O
sometimes	O
magnetometers	O
.	O
</s>
<s>
Gyroscopes	B-Application
measure	O
angular	O
velocity	O
.	O
</s>
<s>
Modern	O
inertial	O
measurement	O
units	O
systems	O
(	O
IMU	O
)	O
are	O
based	O
on	O
MEMS	B-Architecture
technology	I-Architecture
allows	O
to	O
track	O
the	O
orientation	O
(	O
roll	O
,	O
pitch	O
,	O
yaw	O
)	O
in	O
space	O
with	O
high	O
update	O
rates	O
and	O
minimal	O
latency	O
.	O
</s>
<s>
Gyroscopes	B-Application
are	O
always	O
used	O
for	O
rotational	O
tracking	O
,	O
but	O
different	O
techniques	O
are	O
used	O
for	O
positional	B-Operating_System
tracking	I-Operating_System
based	O
on	O
factors	O
like	O
cost	O
,	O
ease	O
of	O
setup	O
,	O
and	O
tracking	O
volume	O
.	O
</s>
<s>
The	O
dead	O
reckoning	O
update	O
rate	O
and	O
prediction	O
algorithm	O
used	O
in	O
a	O
virtual	B-Application
reality	I-Application
system	O
affect	O
the	O
user	O
experience	O
,	O
but	O
there	O
is	O
no	O
consensus	O
on	O
best	O
practices	O
as	O
many	O
different	O
techniques	O
have	O
been	O
used	O
.	O
</s>
<s>
It	O
is	O
hard	O
to	O
rely	O
only	O
on	O
inertial	O
tracking	O
to	O
determine	O
the	O
precise	O
position	O
because	O
dead	O
reckoning	O
leads	O
to	O
drift	O
,	O
so	O
this	O
type	O
of	O
tracking	O
is	O
not	O
used	O
in	O
isolation	O
in	O
virtual	B-Application
reality	I-Application
.	O
</s>
<s>
A	O
lag	O
between	O
the	O
user	O
's	O
movement	O
and	O
virtual	B-Application
reality	I-Application
display	O
of	O
more	O
than	O
100ms	O
has	O
been	O
found	O
to	O
cause	O
nausea	O
.	O
</s>
<s>
Many	O
applications	O
of	O
virtual	B-Application
reality	I-Application
need	O
to	O
not	O
only	O
track	O
the	O
users’	O
head	O
rotations	O
,	O
but	O
also	O
how	O
their	O
bodies	O
move	O
with	O
them	O
(	O
left/right	O
,	O
back/forth	O
,	O
up/down	O
)	O
.	O
</s>
<s>
Six	O
degrees	O
of	O
freedom	O
capability	O
is	O
not	O
necessary	O
for	O
all	O
virtual	B-Application
reality	I-Application
experiences	O
,	O
but	O
it	O
is	O
useful	O
when	O
the	O
user	O
needs	O
to	O
move	O
things	O
other	O
than	O
their	O
head	O
.	O
</s>
<s>
Acoustic	O
tracking	B-Operating_System
systems	I-Operating_System
use	O
techniques	O
for	O
identifying	O
an	O
object	O
or	O
device	O
's	O
position	O
similar	O
to	O
those	O
found	O
naturally	O
in	O
animals	O
that	O
use	O
echolocation	O
.	O
</s>
<s>
Analogous	O
to	O
bats	O
locating	O
objects	O
using	O
differences	O
in	O
soundwave	O
return	O
times	O
to	O
their	O
two	O
ears	O
,	O
acoustic	O
tracking	B-Operating_System
systems	I-Operating_System
in	O
VR	O
may	O
use	O
sets	O
of	O
at	O
least	O
three	O
ultrasonic	O
sensors	O
and	O
at	O
least	O
three	O
ultrasonic	O
transmitters	O
on	O
devices	O
in	O
order	O
to	O
calculate	O
the	O
position	O
and	O
orientation	O
of	O
an	O
object	O
(	O
e.g.	O
</s>
<s>
Because	O
at	O
least	O
three	O
receivers	O
are	O
required	O
,	O
these	O
calculations	O
are	O
commonly	O
known	O
as	O
triangulation	B-Algorithm
.	O
</s>
<s>
Because	O
magnetic	O
tracking	O
does	O
not	O
require	O
a	O
head-mounted	B-General_Concept
display	I-General_Concept
,	O
which	O
are	O
frequently	O
used	O
in	O
virtual	B-Application
reality	I-Application
,	O
it	O
is	O
often	O
the	O
tracking	B-Operating_System
system	I-Operating_System
used	O
in	O
fully	O
immersive	O
virtual	B-Application
reality	I-Application
displays	O
.	O
</s>
<s>
Conventional	O
equipment	O
like	O
head-mounted	B-General_Concept
displays	I-General_Concept
are	O
obtrusive	O
to	O
the	O
user	O
in	O
fully	O
enclosed	O
virtual	B-Application
reality	I-Application
experiences	O
,	O
so	O
alternative	O
equipment	O
such	O
as	O
that	O
used	O
in	O
magnetic	O
tracking	O
is	O
favored	O
.	O
</s>
<s>
Magnetic	O
tracking	O
has	O
been	O
implemented	O
by	O
Polhemus	O
and	O
in	O
Razor	B-Device
Hydra	I-Device
by	I-Device
Sixense	I-Device
.	O
</s>
