<s>
The	O
Persistence	O
of	O
Vision	O
Ray	B-Algorithm
Tracer	I-Algorithm
,	O
most	O
commonly	O
acronymed	O
as	O
POV-Ray	B-Application
,	O
is	O
a	O
cross-platform	B-Operating_System
ray-tracing	B-Algorithm
program	O
that	O
generates	O
images	O
from	O
a	O
text-based	B-Application
scene	I-Application
description	I-Application
.	O
</s>
<s>
It	O
was	O
originally	O
based	O
on	O
DKBTrace	B-Application
,	O
written	O
by	O
David	O
Kirk	O
Buck	O
and	O
Aaron	O
A	O
.	O
Collins	O
for	O
Amiga	B-Device
computers	I-Device
.	O
</s>
<s>
There	O
are	O
also	O
influences	O
from	O
the	O
earlier	O
Polyray	O
raytracer	B-Algorithm
because	O
of	O
contributions	O
from	O
its	O
author	O
,	O
Alexander	O
Enzmann	O
.	O
</s>
<s>
POV-Ray	B-Application
is	O
free	B-License
and	I-License
open-source	I-License
software	I-License
,	O
with	O
the	O
source	O
code	O
available	O
under	O
the	O
AGPL-3.0-or-later	B-Application
license	B-License
.	O
</s>
<s>
Sometime	O
in	O
the	O
1980s	O
,	O
David	O
Kirk	O
Buck	O
downloaded	O
the	O
source	O
code	O
for	O
a	O
Unix	B-Application
ray	B-Algorithm
tracer	I-Algorithm
to	O
his	O
Amiga	B-Device
.	O
</s>
<s>
He	O
experimented	O
with	O
it	O
for	O
a	O
while	O
and	O
eventually	O
decided	O
to	O
write	O
his	O
own	O
ray	B-Algorithm
tracer	I-Algorithm
named	O
DKBTrace	B-Application
after	O
his	O
initials	O
.	O
</s>
<s>
He	O
posted	O
it	O
to	O
the	O
"	O
You	O
Can	O
Call	O
Me	O
Ray	O
"	O
bulletin	B-Application
board	I-Application
system	I-Application
(	O
BBS	O
)	O
in	O
Chicago	O
,	O
thinking	O
others	O
might	O
be	O
interested	O
in	O
it	O
.	O
</s>
<s>
In	O
1987	O
,	O
Aaron	O
A	O
.	O
Collins	O
downloaded	O
DKBTrace	B-Application
and	O
began	O
working	O
on	O
an	O
x86	B-Operating_System
port	O
of	O
it	O
.	O
</s>
<s>
Thus	O
,	O
in	O
July	O
1991	O
,	O
David	O
turned	O
over	O
the	O
project	O
to	O
a	O
team	O
of	O
programmers	O
working	O
in	O
the	O
"	O
GraphDev	O
"	O
forum	B-Application
on	O
CompuServe	O
.	O
</s>
<s>
The	O
name	O
"	O
STAR-Light	O
"	O
(	O
Software	O
Taskforce	O
on	O
Animation	O
and	O
Rendering	O
)	O
was	O
initially	O
used	O
,	O
but	O
eventually	O
the	O
name	O
became	O
"	O
PV-Ray	O
"	O
,	O
and	O
then	O
ultimately	O
"	O
POV-Ray	B-Application
"	O
(	O
Persistence	O
of	O
Vision	O
Ray	B-Algorithm
Tracer	I-Algorithm
)	O
,	O
a	O
name	O
inspired	O
by	O
Dalí	O
's	O
painting	O
,	O
The	O
Persistence	O
of	O
Memory	O
.	O
</s>
<s>
Features	O
of	O
the	O
application	O
,	O
and	O
a	O
summary	O
of	O
its	O
history	O
,	O
are	O
discussed	O
in	O
a	O
February	O
2008	O
interview	O
with	O
David	O
Kirk	O
Buck	O
and	O
Chris	O
Cason	O
on	O
episode	O
24	O
of	O
FLOSS	B-License
Weekly	O
.	O
</s>
<s>
POV-Ray	B-Application
has	O
matured	O
substantially	O
since	O
it	O
was	O
created	O
.	O
</s>
<s>
One	O
of	O
POV-Ray	B-Application
'	O
s	O
main	O
attractions	O
is	O
its	O
large	O
collection	O
of	O
third-party-made	O
assets	O
and	O
tools	O
.	O
</s>
<s>
It	O
is	O
also	O
a	O
useful	O
reference	O
for	O
those	O
wanting	O
to	O
learn	O
how	O
ray	B-Algorithm
tracing	I-Algorithm
and	O
related	O
3D	O
geometry	O
and	O
computer	O
graphics	O
algorithms	O
work	O
.	O
</s>
<s>
The	O
current	O
official	O
version	O
of	O
POV-Ray	B-Application
is	O
3.7	O
.	O
</s>
<s>
In	O
July	O
2006	O
,	O
Intel	O
Corporation	O
started	O
using	O
the	O
beta	O
version	O
of	O
3.7	O
to	O
demonstrate	O
their	O
new	O
dual-core	B-Architecture
Conroe	O
processor	O
due	O
to	O
the	O
efficiency	O
of	O
the	O
SMP	B-Operating_System
(	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
)	O
implementation	O
.	O
</s>
<s>
POV-Ray	B-Application
,	O
in	O
addition	O
to	O
standard	O
3D	O
geometric	O
shapes	O
like	O
tori	O
,	O
spheres	O
,	O
and	O
heightfields	B-Data_Structure
,	O
supports	O
mathematically	O
defined	O
primitives	B-Algorithm
such	O
as	O
the	O
isosurface	O
(	O
a	O
finite	O
approximation	O
of	O
an	O
arbitrary	O
function	O
)	O
,	O
the	O
polynomial	O
primitive	B-Algorithm
(	O
an	O
infinite	B-Application
object	O
defined	O
by	O
a	O
15th	O
order	O
or	O
lower	O
polynomial	O
)	O
,	O
the	O
julia	B-Language
fractal	I-Language
(	O
a	O
3-dimensional	O
slice	O
of	O
a	O
4-dimensional	O
fractal	O
)	O
,	O
the	O
superquadratic	O
ellipsoid	O
(	O
an	O
intermediate	O
between	O
a	O
sphere	O
and	O
a	O
cube	O
)	O
,	O
and	O
the	O
parametric	O
primitive	B-Algorithm
(	O
using	O
equations	O
that	O
represent	O
its	O
surface	O
,	O
rather	O
than	O
its	O
interior	O
)	O
.	O
</s>
<s>
POV-Ray	B-Application
internally	O
represents	O
objects	O
using	O
their	O
mathematical	O
definitions	O
;	O
all	O
POV-Ray	B-Application
primitive	B-Algorithm
objects	O
can	O
be	O
described	O
by	O
mathematical	O
functions	O
.	O
</s>
<s>
This	O
is	O
different	O
from	O
many	O
computer	O
programs	O
that	O
include	O
3D	O
models	O
,	O
which	O
typically	O
use	O
triangle	O
meshes	B-Algorithm
to	O
compose	O
all	O
the	O
objects	O
in	O
a	O
scene	O
.	O
</s>
<s>
This	O
fact	O
provides	O
POV-Ray	B-Application
with	O
several	O
advantages	O
and	O
disadvantages	O
over	O
other	O
rendering	O
and	O
modeling	O
systems	O
;	O
POV-Ray	B-Application
primitives	B-Algorithm
are	O
more	O
accurate	O
than	O
their	O
polygonal	O
counterparts	O
:	O
objects	O
that	O
can	O
be	O
described	O
in	O
terms	O
of	O
spheres	O
,	O
planar	O
surfaces	O
,	O
cylinders	O
,	O
tori	O
,	O
and	O
the	O
like	O
,	O
are	O
perfectly	O
smooth	O
and	O
mathematically	O
accurate	O
in	O
POV-Ray	B-Application
renderings	O
,	O
whereas	O
polygonal	O
artifacts	O
may	O
be	O
visible	O
in	O
mesh-based	O
modeling	O
software	O
.	O
</s>
<s>
POV-Ray	B-Application
primitives	B-Algorithm
are	O
also	O
simpler	O
to	O
define	O
than	O
most	O
of	O
their	O
polygonal	O
counterparts	O
,	O
e.g.	O
,	O
in	O
POV-Ray	B-Application
,	O
a	O
sphere	O
is	O
described	O
simply	O
by	O
its	O
center	O
and	O
radius	O
;	O
in	O
a	O
mesh-based	O
environment	O
,	O
a	O
sphere	O
must	O
be	O
described	O
by	O
a	O
multitude	O
of	O
small	O
connected	O
polygons	O
(	O
usually	O
quads	O
or	O
triangles	O
)	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
script-based	O
primitive	B-Algorithm
modeling	O
is	O
not	O
always	O
a	O
practical	O
method	O
to	O
create	O
certain	O
objects	O
,	O
such	O
as	O
realistic	O
characters	O
or	O
complex	O
man-made	O
artifacts	O
like	O
cars	O
.	O
</s>
<s>
Those	O
objects	O
can	O
and	O
should	O
be	O
created	O
first	O
in	O
mesh-based	O
modeling	O
applications	O
such	O
as	O
Wings	B-Application
3D	I-Application
and	O
Blender	B-Application
,	O
and	O
then	O
they	O
can	O
be	O
converted	O
to	O
POV-Ray	B-Application
'	O
s	O
own	O
mesh	B-Algorithm
format	O
.	O
</s>
<s>
The	O
following	O
is	O
an	O
example	O
of	O
the	O
scene	B-Application
description	I-Application
language	I-Application
used	O
by	O
POV-Ray	B-Application
to	O
describe	O
a	O
scene	O
to	O
render	O
.	O
</s>
<s>
The	O
POV-Ray	B-Application
program	O
itself	O
does	O
not	O
include	O
a	O
modeling	O
feature	O
;	O
it	O
is	O
essentially	O
a	O
pure	O
renderer	O
with	O
a	O
sophisticated	O
model	O
description	O
language	O
.	O
</s>
<s>
To	O
accompany	O
this	O
feature	O
set	O
,	O
third	O
parties	O
have	O
developed	O
a	O
large	O
variety	O
of	O
modeling	O
software	O
,	O
some	O
specialized	O
for	O
POV-Ray	B-Application
,	O
others	O
supporting	O
import	O
and	O
export	O
of	O
its	O
data	O
structures	O
,	O
including	O
the	O
free	B-License
and	I-License
open-source	I-License
3D	O
creation	O
suite	O
.	O
</s>
<s>
A	O
number	O
of	O
additional	O
POV-Ray	B-Application
compatible	O
modelers	O
are	O
linked	O
from	O
.	O
</s>
<s>
In	O
2007	O
,	O
POV-Ray	B-Application
acquired	O
the	O
rights	O
to	O
,	O
an	O
interactive	O
3-D	O
modeling	O
program	O
long	O
used	O
with	O
POV-Ray	B-Application
.	O
</s>
<s>
Official	O
modifications	O
to	O
the	O
POV-Ray	B-Application
source	O
tree	O
are	O
done	O
and/or	O
approved	O
by	O
the	O
POV-Team	O
.	O
</s>
<s>
Most	O
patch	O
submission	O
and/or	O
bug	O
reporting	O
is	O
done	O
in	O
the	O
POV-Ray	B-Application
newsgroups	O
on	O
the	O
news	B-Application
server	O
(	O
with	O
a	O
Web	O
interface	O
)	O
.	O
</s>
<s>
Since	O
POV-Ray	B-Application
'	O
s	O
source	O
is	O
available	O
there	O
are	O
unofficial	O
forks	B-Application
and	O
patched	O
versions	O
of	O
POV-Ray	B-Application
available	O
from	O
third	O
parties	O
;	O
however	O
,	O
these	O
are	O
not	O
officially	O
supported	O
by	O
the	O
POV-Team	O
.	O
</s>
<s>
Official	O
POV-Ray	B-Application
versions	O
currently	O
do	O
not	O
support	O
shader	O
plug-ins	O
.	O
</s>
<s>
Some	O
features	O
,	O
like	O
radiosity	O
and	O
splines	B-Algorithm
are	O
still	O
in	O
development	O
and	O
may	O
be	O
subject	O
to	O
syntactical	O
change	O
.	O
</s>
<s>
POV-Ray	B-Application
3.6	O
is	O
distributed	O
in	O
compiled	B-Language
format	O
for	O
Mac	B-Device
,	O
Windows	B-Application
and	O
Linux	B-Application
.	O
</s>
<s>
Support	O
for	O
Intel	B-Device
Macs	I-Device
is	O
not	O
available	O
in	O
the	O
Mac	B-Device
version	O
,	O
but	O
since	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
is	O
a	O
version	O
of	O
Unix	B-Application
the	O
Linux	B-Application
version	O
can	O
be	O
compiled	B-Language
on	O
it	O
.	O
</s>
<s>
The	O
3.7	O
versions	O
with	O
SMP	B-Operating_System
support	O
are	O
officially	O
supported	O
for	O
Windows	B-Application
and	O
Linux	B-Application
.	O
</s>
<s>
Unofficial	O
Mac	B-Device
versions	O
for	O
v3.7	O
can	O
be	O
found	O
.	O
</s>
<s>
POV-Ray	B-Application
can	O
be	O
ported	O
to	O
any	O
platform	O
which	O
has	O
a	O
compatible	O
C++	B-Language
compiler	B-Language
.	O
</s>
<s>
Originally	O
,	O
POV-Ray	B-Application
was	O
distributed	O
under	O
its	O
own	O
POV-Ray	B-Application
License	B-License
.	O
</s>
<s>
Namely	O
,	O
the	O
POV-Ray	B-Application
3.6	O
Distribution	O
License	B-License
and	O
the	O
POV-Ray	B-Application
3.6	O
Source	O
License	B-License
,	O
which	O
permitted	O
free	O
distribution	O
of	O
the	O
program	O
source	O
code	O
and	O
binaries	O
,	O
but	O
restricts	O
commercial	O
distribution	O
and	O
the	O
creation	O
of	O
derivative	O
works	O
other	O
than	O
fully	O
functional	O
versions	O
of	O
POV-Ray	B-Application
.	O
</s>
<s>
Although	O
the	O
source	O
code	O
of	O
older	O
versions	O
is	O
available	O
for	O
modification	O
,	O
due	O
to	O
the	O
above	O
3.6	O
and	O
prior	O
license	B-License
restrictions	O
,	O
it	O
was	O
not	O
open	B-Application
source	I-Application
or	O
free	B-Application
software	I-Application
according	O
to	O
the	O
OSI	O
or	O
the	O
FSF	B-Operating_System
definition	O
of	O
the	O
term	O
.	O
</s>
<s>
This	O
was	O
a	O
problem	O
as	O
source	O
code	O
exchange	O
with	O
the	O
greater	O
FOSS	B-License
ecosystem	O
was	O
impossible	O
due	O
to	O
License	B-License
incompatibility	O
with	O
copyleft	B-License
licenses	I-License
.	O
</s>
<s>
One	O
of	O
the	O
reasons	O
that	O
POV-Ray	B-Application
was	O
not	O
originally	O
licensed	O
under	O
the	O
free	B-Application
software	I-Application
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
,	O
or	O
other	O
open	B-Application
source	I-Application
licenses	O
,	O
is	O
that	O
POV-Ray	B-Application
was	O
developed	O
before	O
the	O
GPL-style	O
licenses	O
became	O
widely	O
used	O
;	O
the	O
developers	O
wrote	O
their	O
own	O
license	B-License
for	O
the	O
release	O
of	O
POV-Ray	B-Application
,	O
and	O
contributors	O
to	O
the	O
software	O
worked	O
under	O
the	O
assumption	O
their	O
contributions	O
would	O
be	O
licensed	O
under	O
the	O
POV-Ray	B-Application
3.6	O
Licenses	O
.	O
</s>
<s>
In	O
2013	O
,	O
with	O
version	O
3.7	O
,	O
POV-Ray	B-Application
was	O
relicensed	O
under	O
the	O
Affero	O
General	B-License
Public	I-License
License	I-License
version	O
3	O
(	O
or	O
later	O
)	O
.	O
</s>
<s>
Thus	O
POV-Ray	B-Application
is	O
since	O
then	O
free	B-Application
software	I-Application
according	O
to	O
the	O
FSF	B-Operating_System
definition	O
and	O
also	O
open	B-Application
source	I-Application
software	I-Application
according	O
to	O
the	B-License
Open	I-License
Source	I-License
Definition	I-License
.	O
</s>
