Roulette (curve) in this case, the point lies on the circle then the roulette is a cycloid. A related concept is a glissette, the curve described by a point attached to a given curve as it slides along two (or more) given curves. Formally speaking, the curves must be differentiable curves in the Euclidean plane. The "fixed curve" is kept invariant; the "rolling curve" is subjected to a continuous congruence transformation such that at all times the curves are tangent at a point of contact that moves with the same speed when taken along either curve (another way to express this constraint
Intersection curve has to fulfill the condition formula_29, because formula_28 has to be a tangent vector, which means any contour point is a point of the intersection curve of the two implicit surfaces For quadrics, formula_32 is always a linear function. Hence the contour line of a quadric is always a plane section (i.e. a conic section). The contour line of the surface formula_33 (see picture) was traced by the marching method. "Remark:" The determination of a contour polygon of a parametric surface formula_34 needs tracing an implicit curve in parameter plane. The intersection curve of two polyhedrons is a polygon (see