clothoid

Moves the turtle length forward along a clothoid (Euler spiral): the curvature changes linearly with the distance travelled, from startCurvature to endCurvature, in radians per unit of length, so the turtle turns by (startCurvature + endCurvature) / 2 · length radians in total. Clothoids join straight lines and arcs without jumps in curvature, as in road and track design. See curve.