“…Several kinds of design methods have been proposed to solve this problem, such as the optimization method [1], the simultaneous multiple surface design method [2], the first-order partial differential equation method [3], the method of ellipsoids [4], the method of ray mapping with subsequent surface reconstruction [5] and the Monge-Ampére (MA) equation method [6][7][8]. Most of these methods rely on the point source assumption, and the MA method that satisfies the integrability condition automatically could be the most advanced point source algorithm [9].…”