alessandrozamberletti/docdetect

# -*- coding: utf-8 -*-
import numpy as np
import itertools
from docdetect.line_utils import lines_angle


def find_intersections(lines, im, angle_thr=45):
    height, width = im.shape[:2]
    intersections = []
    vertex_id = 0
    for line1, line2 in itertools.permutations(lines, 2):
        if _angles_are_similar(line1, line2, angle_thr):
            continue
        coords = _find_intersection_coords(line1, line2)
        if _coords_are_valid(coords, width, height) and not _already_present(coords, intersections):
            intersections.append({"id": vertex_id,
                                  "lines": (line1, line2),
                                  "coords": coords})
            vertex_id += 1
    return intersections


def _find_intersection_coords(line1, line2):
    rho1, theta1 = line1
    rho2, theta2 = line2
    a = [[np.cos(theta1), np.sin(theta1)], [np.cos(theta2), np.sin(theta2)]]
    b = [[rho1], [rho2]]
    try:
        # aX = b, solve for x
        x, y = np.round(np.linalg.solve(a, b))
        return int(x), int(y)
    except np.linalg.linalg.LinAlgError:
        # singular matrix
        return -1, -1


def _already_present(coords, intersections):
    return (
        True
        if any(intersection["coords"] == coords for intersection in intersections)
        else False
    )


def _angles_are_similar(line1, line2, angle_thr):
    return lines_angle(line1, line2) < angle_thr


def _coords_are_valid(coords, width, height):
    return 0 < coords[0] < width and 0 < coords[1] < height