<s>
A	O
3D	B-Algorithm
Content	I-Algorithm
Retrieval	I-Algorithm
system	O
is	O
a	O
computer	O
system	O
for	O
browsing	O
,	O
searching	O
and	O
retrieving	O
three	O
dimensional	O
digital	O
contents	O
(	O
e.g.	O
</s>
<s>
:	O
Computer-aided	B-Application
design	I-Application
,	O
molecular	O
biology	O
models	O
,	O
and	O
cultural	O
heritage	O
3D	O
scenes	O
,	O
etc	O
.	O
)	O
</s>
<s>
The	O
most	O
original	O
way	O
of	O
doing	O
3D	B-Algorithm
content	I-Algorithm
retrieval	I-Algorithm
uses	O
methods	O
to	O
add	O
description	O
text	O
to	O
3D	O
content	O
files	O
such	O
as	O
the	O
content	O
file	O
name	O
,	O
link	O
text	O
,	O
and	O
the	O
web	O
page	O
title	O
so	O
that	O
related	O
3D	O
content	O
can	O
be	O
found	O
through	O
text	O
retrieval	O
.	O
</s>
<s>
Thus	O
,	O
shape	O
matching	O
methods	O
for	O
3D	B-Algorithm
content	I-Algorithm
retrieval	I-Algorithm
have	O
become	O
popular	O
.	O
</s>
<s>
The	O
skeleton	O
encodes	O
the	O
geometric	O
and	O
topological	O
information	O
in	O
the	O
form	O
of	O
a	O
skeletal	O
graph	O
and	O
uses	O
graph	B-General_Concept
matching	I-General_Concept
techniques	O
to	O
match	O
the	O
skeletons	O
and	O
compare	O
them	O
.	O
</s>
<s>
The	O
skeleton	O
3D	B-Algorithm
retrieval	I-Algorithm
method	O
needs	O
more	O
time	O
and	O
effort	O
before	O
it	O
can	O
be	O
used	O
widely	O
.	O
</s>
<s>
Shape	O
histograms	B-Algorithm
,	O
feature	O
vectors	O
composed	O
of	O
global	O
geo-metic	O
properties	O
such	O
as	O
circularity	O
and	O
eccentricity	O
,	O
and	O
feature	O
vectors	O
created	O
using	O
frequency	O
decomposition	O
of	O
spherical	O
functions	O
are	O
common	O
examples	O
of	O
using	O
statistical	O
methods	O
to	O
describe	O
3D	O
information	O
.	O
</s>
<s>
Prototypical	B-Application
Views	O
and	O
Light	O
field	O
description	O
are	O
good	O
examples	O
of	O
2D	O
projection	O
methods	O
.	O
</s>
<s>
In	O
Purdue	O
University	O
,	O
researchers	O
led	O
by	O
Professor	O
Karthik	O
Ramani	O
at	O
the	O
Research	O
and	O
Education	O
Center	O
for	O
Information	O
created	O
a	O
3D	B-Algorithm
search	I-Algorithm
engine	I-Algorithm
called	O
the	O
3D	O
Engineering	O
Search	O
System	O
(	O
3DESS	O
)	O
.	O
</s>
<s>
The	O
mechanism	O
behind	O
this	O
search	O
engine	O
is	O
that	O
it	O
starts	O
from	O
an	O
algorithm	O
which	O
can	O
transform	O
query	O
drawing	O
to	O
voxels	B-Algorithm
,	O
then	O
extracts	O
the	O
most	O
important	O
shape	O
information	O
from	O
the	O
voxels	B-Algorithm
by	O
using	O
another	O
algorithm	O
called	O
thinning	O
,	O
and	O
formulates	O
a	O
skeleton	O
of	O
the	O
object	O
’s	O
outlines	O
and	O
topology	B-Architecture
.	O
</s>
<s>
With	O
the	O
skeleton	O
modeling	O
3D	B-Algorithm
retrieval	I-Algorithm
method	O
,	O
figuring	O
out	O
an	O
efficient	O
way	O
to	O
index	O
3D	O
shape	O
descriptors	O
is	O
very	O
challenging	O
because	O
3D	O
shape	O
indexing	O
has	O
very	O
strict	O
criteria	O
.	O
</s>
<s>
In	O
order	O
to	O
make	O
the	O
3D	O
search	O
interface	O
simple	O
enough	O
for	O
novice	O
users	O
who	O
know	O
little	O
on	O
3D	B-Algorithm
retrieval	I-Algorithm
input	O
source	O
requirements	O
,	O
a	O
multimodal	B-Application
retrieval	O
system	O
,	O
which	O
can	O
take	O
various	O
types	O
of	O
input	O
sources	O
and	O
provide	O
robust	O
query	O
results	O
,	O
is	O
necessary	O
.	O
</s>
<s>
(	O
2003	O
)	O
,	O
the	O
proposed	O
“	O
Princeton	O
3D	B-Algorithm
search	I-Algorithm
engine	I-Algorithm
”	O
supports	O
2D	O
sketches	O
,	O
3D	O
sketches	O
,	O
3D	O
models	O
and	O
text	O
as	O
queries	O
.	O
</s>
<s>
(	O
2003	O
)	O
,	O
he	O
designed	O
a	O
3D	B-Algorithm
retrieval	I-Algorithm
system	O
that	O
intakes	O
2D	O
sketches	O
and	O
retrieves	O
for	O
3D	O
objects	O
.	O
</s>
<s>
(	O
2007	O
)	O
proposed	O
a	O
3D	B-Algorithm
retrieval	I-Algorithm
framework	O
using	O
2D	O
photographic	O
images	O
,	O
sketches	O
,	O
and	O
3D	O
models	O
.	O
</s>
