Clipper: Crashing When Clipping Open Polygons

Question

I am trying to use Clipper, an open source polygon clipping library, to clip an open polygon with a closed polygon.

I am using the python wrapper of pyclipper. My code is as follows:

import pyclipper

subj = [[-10, 5], [20, 5]]

clip = [[0, 0], [0, 10], [10, 10], [10, 0]]

pc = pyclipper.Pyclipper()

pc.AddPath(clip, pyclipper.PT_CLIP, True)
pc.AddPath(subj, pyclipper.PT_SUBJECT, False)

solution = pc.Execute(pyclipper.CT_INTERSECTION, pyclipper.PFT_EVENODD, pyclipper.PFT_EVENODD)

print(solution)

It seems to run up until the Execute function, then it just quits with no error message. What am I doing wrong?

developer_hatch · Answer 1 · 2017-06-21T20:06:00.227

0

try changing your list of list for tuples, and the most important, to don't have a type error, use Pyclipper::Execute2:

import pyclipper

subj = [(-10, 5), (20, 5)]

clip = [(0, 0), (0, 10), (10, 10), (10, 0)]

pc = pyclipper.Pyclipper()

pc.AddPath(clip, pyclipper.PT_CLIP, True)
pc.AddPath(subj, pyclipper.PT_SUBJECT, False)

solution = pc.Execute2(pyclipper.CT_INTERSECTION, pyclipper.PFT_NONZERO, pyclipper.PFT_NONZERO)


print([i.Contour for i in solution.Childs])

[[[10, 5], [0, 5]]]

the last line is equivalent, in your case, to:

solution = pc.Execute2(pyclipper.CT_INTERSECTION, pyclipper.PFT_EVENODD, pyclipper.PFT_EVENODD)

edited Jun 21 '17 at 20:06

answered Jun 21 '17 at 19:25

developer_hatch

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AddPaths is to add multiple paths at once, I'm only adding one path... I tested it anyway and got an error. – Adam C Jun 21 '17 at 19:33
@AdamCavender a last observation, why do you have the second parameter in False? Did you try set it as True? – developer_hatch Jun 21 '17 at 19:37
I set it to False becuase that is a parameter for whether the polygon is closed or not. – Adam C Jun 21 '17 at 19:38
@AdamCavender I made a little change, I hope that's what you're looking at, see that I added a value at the end so the shape can close. – developer_hatch Jun 21 '17 at 19:51
That makes it a triangle, not a line. Thanks for trying to help but I don't think you understand how Clipper or how polygons work. – Adam C Jun 21 '17 at 19:53
@AdamCavender I don't give up, let me know if that line was that you were looking at – developer_hatch Jun 21 '17 at 20:01

Clipper: Crashing When Clipping Open Polygons

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