An Isoptic Curve formed from the locus of Tangents meeting at Right Angles. The orthoptic of a Parabola is its Directrix. The orthoptic of a central Conic was investigated by Monge and is a Circle concentric with the Conic Section. The orthoptic of an Astroid is a Circle.
|Cardioid||Circle or Limaçon|
|Logarithmic Spiral||equal Logarithmic Spiral|
Lawrence, J. D. A Catalog of Special Plane Curves. New York: Dover, pp. 58 and 207, 1972.