A plane quartic curve also called the cross curve or policeman on point duty curve (Cundy and Rollett 1989). It is given by the implicit equation
(1)
|
which is equivalent to
(2)
|
and
(3)
|
In parametric form,
(4)
| |||
(5)
|
The curvature is given by
(6)
| |||
(7)
|
which, in the special case , reduces to
(8)
|