<s>
Active	B-General_Concept
shape	I-General_Concept
models	I-General_Concept
(	O
ASMs	O
)	O
are	O
statistical	O
models	O
of	O
the	O
shape	O
of	O
objects	O
which	O
iteratively	O
deform	O
to	O
fit	O
to	O
an	O
example	O
of	O
the	O
object	O
in	O
a	O
new	O
image	O
,	O
developed	O
by	O
Tim	O
Cootes	O
and	O
Chris	O
Taylor	O
in	O
1995	O
.	O
</s>
<s>
The	O
shapes	O
are	O
constrained	O
by	O
the	O
PDM	O
(	O
point	B-General_Concept
distribution	I-General_Concept
model	I-General_Concept
)	O
Statistical	O
Shape	O
Model	O
to	O
vary	O
only	O
in	O
ways	O
seen	O
in	O
a	O
training	O
set	O
of	O
labelled	O
examples	O
.	O
</s>
<s>
Conform	O
the	O
suggested	O
shape	O
to	O
the	O
point	B-General_Concept
distribution	I-General_Concept
model	I-General_Concept
,	O
commonly	O
called	O
a	O
"	O
shape	O
model	O
"	O
in	O
this	O
context	O
.	O
</s>
<s>
It	O
is	O
closely	O
related	O
to	O
the	O
active	B-General_Concept
appearance	I-General_Concept
model	I-General_Concept
.	O
</s>
<s>
It	O
is	O
also	O
known	O
as	O
a	O
"	O
Smart	O
Snakes	B-General_Concept
"	O
method	O
,	O
since	O
it	O
is	O
an	O
analog	O
to	O
an	O
active	B-General_Concept
contour	I-General_Concept
model	I-General_Concept
which	O
would	O
respect	O
explicit	O
shape	O
constraints	O
.	O
</s>
