<s>
In	O
geometry	O
,	O
an	O
isophote	B-Algorithm
is	O
a	O
curve	O
on	O
an	O
illuminated	O
surface	O
that	O
connects	O
points	O
of	O
equal	O
brightness	O
.	O
</s>
<s>
A	O
plane	O
has	O
no	O
isophotes	B-Algorithm
,	O
because	O
every	O
point	O
has	O
the	O
same	O
brightness	O
.	O
</s>
<s>
In	O
astronomy	O
,	O
an	O
isophote	B-Algorithm
is	O
a	O
curve	O
on	O
a	O
photo	O
connecting	O
points	O
of	O
equal	O
brightness	O
.	O
</s>
<s>
In	O
computer-aided	B-Application
design	I-Application
,	O
isophotes	B-Algorithm
are	O
used	O
for	O
checking	O
optically	O
the	O
smoothness	O
of	O
surface	O
connections	O
.	O
</s>
<s>
Hence	O
,	O
the	O
differentiability	O
of	O
the	O
isophotes	B-Algorithm
and	O
their	O
geometric	O
continuity	O
is	O
1	O
less	O
than	O
that	O
of	O
the	O
surface	O
.	O
</s>
<s>
G1-continuous	O
)	O
,	O
the	O
isophotes	B-Algorithm
have	O
there	O
a	O
kink	O
(	O
i.e.	O
</s>
<s>
But	O
the	O
geometric	O
continuity	O
of	O
the	O
isophotes	B-Algorithm
show	O
:	O
on	O
the	O
left	O
side	O
,	O
they	O
have	O
kinks	O
(	O
i.e.	O
</s>
<s>
which	O
can	O
be	O
considered	O
as	O
the	O
intersection	O
curve	O
of	O
two	O
implicit	B-Algorithm
surfaces	I-Algorithm
.	O
</s>
