Iso-optic curve

A plane curve that is the locus of a vertex of given angle $\gamma$ that moves in the plane in such a way that its sides are tangents to a given curve for all positions of the angle. If $\gamma=\pi/2$, then the iso-optic curve is called an ortho-optic curve. For example, the ortho-optic curve of an ellipse is a circle.

References

[1]	A.A. Savelov, "Planar curves" , Moscow (1960) (In Russian)
[a1]	K. Fladt, "Analytische Geometrie spezieller Kurven" , Akad. Verlagsgesell. (1962)
[a2]	M. Berger, "Geometry" , I , Springer (1987) pp. 232
[a3]	M. Berger, "Geometry" , II , Springer (1987) pp. 239
[a4]	F.G. Texeira, "Traité des courbes spéciales remarquables planes on gauches" , Coïmbre (1908–1915)