Redundant points and undetected overlaps

[Thorreke]

I have a set of rectangles that I want to convert into a single polygon

g = [[(320, -60), (320, 375), (-60, 375), (-60, -60)], [(680, -60), (680, 375), (275, 375), (275, -60)], [(955, 105), (955, 375), (635, 375), (635, 105)], [(1360, -10), (1360, 725), (910, 725), (910, -10)], [(1360, 325), (1360, 725), (855, 725), (855, 325)], [(1360, 680), (1360, 1055), (855, 1055), (855, 680)], [(900, 325), (900, 480), (-60, 480), (-60, 325)], [(900, 435), (900, 880), (725, 880), (725, 435)], [(330, 435), (330, 880), (-60, 880), (-60, 435)], [(390, 700), (390, 880), (-60, 880), (-60, 700)], [(390, 567), (390, 747), (-60, 747), (-60, 567)], [(390, 435), (390, 615), (-60, 615), (-60, 435)], [(775, 435), (775, 880), (345, 880), (345, 435)], [(585, 835), (585, 1145), (140, 1145), (140, 835)], [(190, 835), (190, 1145), (-60, 1145), (-60, 835)]]

shapes = [Primitive.polygon(v) for v in g]

But this operation fails:
combined = reduce(lambda x,y: x|y, shapes)

Traceback (most recent call last):
File "/snap/pycharm-community/439/plugins/python-ce/helpers/pydev/pydevconsole.py", line 364, in runcode
coro = func()
File "", line 1, in
File "", line 1, in
File "/mypath/.venv/lib/python3.10/site-packages/shapepy/shape.py", line 560, in or
new_jordans = FollowPath.or_shapes(self, other)
File "/mypath/.venv/lib/python3.10/site-packages/shapepy/shape.py", line 337, in or_shapes
new_jordans = FollowPath.follow_path(all_jordans, indexs)
File "/mypath/.venv/lib/python3.10/site-packages/shapepy/shape.py", line 279, in follow_path
jordan = FollowPath.indexs_to_jordan(jordans, indices_matrix)
File "/mypath/.venv/lib/python3.10/site-packages/shapepy/shape.py", line 259, in indexs_to_jordan
new_jordan = JordanCurve.from_segments(beziers)
File "/mypath/.venv/lib/python3.10/site-packages/shapepy/jordancurve.py", line 132, in from_segments
assert prev_end_point == next_start_point
AssertionError

Closer inspection reveals some strange things are going on:

For example the following produces a correct result, however there are extra points in the shape.

s = reduce(lambda x,y:x|y,shapes[3:5])
print(s)

Simple Shape of area 352750.00 with vertices:
[[1360. -10.]
[1360. 325.]
[1360. 725.]
[ 910. 725.]
[ 855. 725.]
[ 855. 325.]
[ 910. 325.]
[ 910. -10.]]

This one produces a loop in the outline:

s = reduce(lambda x,y:x|y,shapes[1:3])
print(s)

Simple Shape of area 262575.00 with vertices:
[[680. -60.]
[680. 105.]
[955. 105.]
[955. 375.]
[680. 375.]
[635. 375.]
[635. 105.]
[680. 105.]
[680. 375.]
[635. 375.]
[320. 375.]
[275. 375.]
[275. -60.]
[320. -60.]]

And sometimes it does not even detect the rectangles are overlapping:

s = reduce(lambda x,y:x|y,shapes[0:2])
print(s)
for j in s.jordans:
         print(j)

Disjoint shape with total area 341475.0 and 2 subshapes
Jordan Curve of degree 1 and vertices
((680, -60), (680, 105), (680, 375), (635, 375), (320, 375), (275, 375), (275, -60), (320, -60))
Jordan Curve of degree 1 and vertices
((275, 375), (-60, 375), (-60, -60), (275, -60), (320, -60), (320, 375))

[carlos-adir]

Thank you for the issue. It helps me improving the package !

Indeed, the current implementation has problems when operation with shapes that shares the same edge.
Showing the positions of your points gives that:

Code to generate image

from matplotlib import pyplot as plt
import numpy as np

rectangles = [
    [(320, -60), (320, 375), (-60, 375), (-60, -60)],
    [(680, -60), (680, 375), (275, 375), (275, -60)],
    [(955, 105), (955, 375), (635, 375), (635, 105)],
    [(1360, -10), (1360, 725), (910, 725), (910, -10)],
    [(1360, 325), (1360, 725), (855, 725), (855, 325)],
    [(1360, 680), (1360, 1055), (855, 1055), (855, 680)],
    [(900, 325), (900, 480), (-60, 480), (-60, 325)],
    [(900, 435), (900, 880), (725, 880), (725, 435)],
    [(330, 435), (330, 880), (-60, 880), (-60, 435)],
    [(390, 700), (390, 880), (-60, 880), (-60, 700)],
    [(390, 567), (390, 747), (-60, 747), (-60, 567)],
    [(390, 435), (390, 615), (-60, 615), (-60, 435)],
    [(775, 435), (775, 880), (345, 880), (345, 435)],
    [(585, 835), (585, 1145), (140, 1145), (140, 835)],
    [(190, 835), (190, 1145), (-60, 1145), (-60, 835)],
]

# plot points
all_points = set()
for rectangle in rectangles:
    all_points |= set(tuple(rectangle))
all_points = np.array(tuple(all_points))
for i, rectangle in enumerate(rectangles):
    points = np.array(list(rectangle) + [rectangle[0]])
    plt.plot(points[:, 0], points[:, 1], label=str(i))
plt.scatter(all_points[:, 0], all_points[:, 1], color="k")
plt.gca().set_aspect("equal")
plt.show()

In fact, with only the frist two rectangles it gives the wrong result. The union gives a DisjointShape with jordans:

Jordan Curve of degree 1 and vertices
((680, -60), (680, 375), (320, 375), (275, 375), (275, -60), (320, -60))
Jordan Curve of degree 1 and vertices
((275, 375), (-60, 375), (-60, -60), (275, -60), (320, -60), (320, 375))

I'm working on this to solve the issue.