High Quality Content by WIKIPEDIA articles! For a plane curve C and a given fixed point P, the pedal curve of C is the locus of points X so that PX is perpendicular to a tangent to the curve passing through X. The point P is called the pedal point. The pedal curve is the first in a series of curves C1, C2, C3, etc., where C1 is the pedal of C, C2 is the pedal of C1, and so on. In this scheme, C1 is known as the first positive pedal of C, C2 is the to second positive pedal of C, and so on. Going the other direction, C is the first negative pedal of C1, the second negative pedal of C2, etc.