A PolyCurve2D is a set of piecewise smooth curve arcs, such that the
end of a curve is the beginning of the next curve, and such that they do
not intersect nor self-intersect.
A PolyOrientedCurve2D is a set of piecewise smooth curve arcs, such that the
end of a curve is the beginning of the next curve, and such that they do
not intersect nor self-intersect.