Adaptation of O'Rourke algorithm to compute the intersection points only when necessary -> first steps, many points need to be taken care of
convex polygon intersection with parsimonious computations: the intersection vertices are not actually computed, and only the intersection points with non maximal nor minimal abscissa are output
intersection of convex polygons in FareyFan class -> to be tested
union of DSSs with intersection of convex polygons using O'Rourke algorithm