<s>
A	O
cave	B-General_Concept
automatic	I-General_Concept
virtual	I-General_Concept
environment	I-General_Concept
(	O
better	O
known	O
by	O
the	O
recursive	O
acronym	O
CAVE	O
)	O
is	O
an	O
immersive	O
virtual	B-Application
reality	I-Application
environment	O
where	O
projectors	B-Device
are	O
directed	O
to	O
between	O
three	O
and	O
six	O
of	O
the	O
walls	O
of	O
a	O
room-sized	O
cube	O
.	O
</s>
<s>
The	O
name	O
is	O
also	O
a	O
reference	O
to	O
the	O
allegory	O
of	O
the	O
Cave	O
in	O
Plato	B-Operating_System
's	O
Republic	O
in	O
which	O
a	O
philosopher	O
contemplates	O
perception	O
,	O
reality	O
,	O
and	O
illusion	O
.	O
</s>
<s>
There	O
are	O
typically	O
multiple	O
speakers	O
placed	O
at	O
multiple	O
angles	O
in	O
the	O
CAVE	O
,	O
providing	O
3D	O
sound	O
to	O
complement	O
the	O
3D	B-Algorithm
video	I-Algorithm
.	O
</s>
<s>
A	O
lifelike	O
visual	O
display	O
is	O
created	O
by	O
projectors	B-Device
positioned	O
outside	O
the	O
CAVE	O
and	O
controlled	O
by	O
physical	O
movements	O
from	O
a	O
user	O
inside	O
the	O
CAVE	O
.	O
</s>
<s>
A	O
motion	B-Application
capture	I-Application
system	O
records	O
the	O
real	O
time	O
position	O
of	O
the	O
user	O
.	O
</s>
<s>
Stereoscopic	B-Algorithm
LCD	B-Algorithm
shutter	I-Algorithm
glasses	I-Algorithm
convey	O
a	O
3D	B-Algorithm
image	I-Algorithm
.	O
</s>
<s>
The	O
computers	O
rapidly	O
generate	O
a	O
pair	O
of	O
images	O
,	O
one	O
for	O
each	O
of	O
the	O
user	O
's	O
eyes	O
,	O
based	O
on	O
the	O
motion	B-Application
capture	I-Application
data	O
.	O
</s>
<s>
The	O
glasses	O
are	O
synchronized	O
with	O
the	O
projectors	B-Device
so	O
that	O
each	O
eye	O
only	O
sees	O
the	O
correct	O
image	O
.	O
</s>
<s>
Since	O
the	O
projectors	B-Device
are	O
positioned	O
outside	O
the	O
cube	O
,	O
mirrors	O
are	O
often	O
used	O
to	O
reduce	O
the	O
distance	O
required	O
from	O
the	O
projectors	B-Device
to	O
the	O
screens	O
.	O
</s>
<s>
One	O
or	O
more	O
computers	O
drive	O
the	O
projectors	B-Device
.	O
</s>
<s>
There	O
are	O
3	O
popular	O
scene	B-Data_Structure
graphs	I-Data_Structure
in	O
use	O
today	O
:	O
OpenSG	O
,	O
OpenSceneGraph	O
,	O
and	O
OpenGL	B-Library
Performer	I-Library
.	O
</s>
<s>
OpenSG	O
and	O
OpenSceneGraph	O
are	O
open	O
source	O
;	O
while	O
OpenGL	B-Library
Performer	I-Library
is	O
free	O
,	O
its	O
source	O
code	O
is	O
not	O
included	O
.	O
</s>
<s>
The	O
calibration	O
process	O
depends	O
on	O
the	O
motion	B-Application
capture	I-Application
technology	O
being	O
used	O
.	O
</s>
<s>
The	O
projectors	B-Device
then	O
fill	O
the	O
CAVE	O
with	O
many	O
one-inch	O
boxes	O
set	O
one	O
foot	O
apart	O
.	O
</s>
<s>
This	O
also	O
allows	O
the	O
CAVE	O
to	O
correctly	O
identify	O
where	O
the	O
user	O
is	O
located	O
and	O
can	O
precisely	O
track	O
their	O
movements	O
,	O
allowing	O
the	O
projectors	B-Device
to	O
display	O
images	O
based	O
on	O
where	O
the	O
person	O
is	O
inside	O
the	O
CAVE	O
.	O
</s>
