Indeed, but the convex hull approach also works for multiple sets of points, in any order. As for [2], in the article the data is separated into 16 polygons, s

Indeed, but the convex hull approach also works for multiple sets of points, in any order. As for [2], in the article the data is separated into 16 polygons, so the interior lines are actually shared between polygons. It's still possible to union the polygons, but it takes more time than calculating the convex hull.