yep that paper is extremely impressive! I would love to implement that approach as well, but it is much more computationally expensive. In the Q&A after a talk from that paper's author, he mentions that it takes about 6 hours for the algorithm to run. The approach I took, modeled off of Yue et al, takes about 30 seconds. The trade-off is that the Schwartzburg paper is capable of much more general purpose remapping. It does not require continuity, which is why that paper results in ray folding which you can see as creasing in the lens.