BerGeo/h2/gift_wrapper.py

# Use atan2 instead of acos to calc angle; atan2(x,y) of the point we potentially want to add
from math import acos, sqrt

from profile import Profiler
from util import Vector, Point, gen_point


@Profiler("calculating angle")
def calc_angle(v1: Vector, v2: Vector) -> float:
    dot = (v1.x * v2.x) + (v1.y * v2.y)
    len_1 = sqrt(v1.x**2 + v1.y**2)
    len_2 = sqrt(v2.x**2 + v2.y**2)

    tmp = dot / (len_1 * len_2)
    return acos(max(min(tmp, 1), -1))  # acos is only defined in [-1,1]


@Profiler("calculating vector")
def calc_vector(p1: Point, p2: Point) -> Vector:
    return Vector((p2.x - p1.x), (p2. y - p1.y))


@Profiler("gift_wrapper")
def rapper(points: set):
    min_pt = min(points)
    hull = [min_pt]
    comp_vec = Vector(0, 1)
    with Profiler("iterating points", excluded=("calculating angle", "calculating vector")):
        while True:
            hull.append(min(points - {hull[-1]},
                            key=lambda p: calc_angle(comp_vec, calc_vector(hull[-1], p))))

            comp_vec = calc_vector(hull[-2], hull[-1])

            if hull[-1] == min_pt:
                return hull


if __name__ == '__main__':
    points = {gen_point() for _ in range(30)}
    hull = rapper(points)