Edge-Unfolding Nearly Flat Convex Caps

The main result of this paper is a proof that a nearly flat, acutely triangulated convex cap C in ℝ3 has an edge-unfolding to a non-overlapping polygon in the plane. A convex cap is the intersection of the surface of a convex polyhedron and a halfspace. Nearly flat means that every outer face normal forms a sufficiently small angle φ \u3c Φ with the z-axis orthogonal to the halfspace bounding plane. The size of Φ depends on the acuteness gap α: if every triangle angle is at most π/2 - α, then Φ ≈ 0.36√α suffices; e.g., for α = 3°, Φ ≈ 5°. The proof employs the recent concepts of angle-monotone and radially monotone curves. The proof is constructive, leading to a polynomial-time algorithm for finding the edge-cuts, at worst O(n); a version has been implemented