On Tue, Apr 4, 2017 at 6:48 PM, Aaron Meurer <[email protected]> wrote:
>
> On Tue, Apr 4, 2017 at 6:45 PM Aaron Meurer <[email protected]> wrote:
>>
>> On Tue, Apr 4, 2017 at 5:12 AM <[email protected]> wrote:
>>>>
>>>> geometry.intersection doesn't work in this scenario
>>>
>>> In what sense in doesn't work? Is it broken?
>>>
>>> You can find if a circle is wholly inside a polygon in two steps:
>>> 1) find if they intersect each other:
>>> your_polygon = Polygon(Point(a, b), ...)
>>> your_circle = Circle(Point(c, d), radius)
>>> your_polygon.intersection(your_circle)
>>> If you get empty list you know that circle is inside the polygon or
>>> polygon is inside the circle.
>>>
>>> 2)Now you should check if random point from circle is enclosed by
>>> polygon:
>>> your_ polygon.encloses_point(your_circle.random_point())
>>> If you get True, you know that circle is inside polygon.
>>
>>
>> Won't this also pass sometimes if the polygon is inside the circle?
>>
>> I think you would need to pick random points in each until you find one
>> that is in one and not the other. However, if the circle circumscribes the
>> polygon and it is very convex (or the other way around), there may be a low
>> probability of finding the desired point. So a more direct solution would be
>> preferred.
>
>
> And you also have to handle the case where neither is inside the other (this
> random points method won't help you here).
I suppose that case is still handled. I believe the correct algorithm
is something like:
contains(A, B) (pseudocode):
if A and B intersect, then
return False
while True
Let a be a random point in A and b a random point in B
if a is in B and b is in A, then
continue
if a is in B and b is not in A, then
return B is inside of A
if a is not in B and b is in A, then
return A is inside of B
if a is not in B and b is not in A, then
return False (the sets are disjoint, because of the
intersection check above)
But again, it is not hard to construct examples where the probability
of finding a point in the symmetric difference is low, meaning the
loop will take a long time. Perhaps instead of checking points in the
shape, you should check points on the boundary. If the intersection
check is correct, the first case (a in B and b in A) will be
impossible.
Aaron Meurer
>
> Aaron Meurer
>>
>>
>> Aaron Meurer
>>
>>>
>>>
>>> Szymon
>>>
>>> W dniu poniedziałek, 3 kwietnia 2017 23:53:03 UTC+2 użytkownik Bron
>>> Davies napisał:
>>>>
>>>> How can I tell if a circle is wholly inside a polygon?
>>>> geometry.intersection doesn't work in this scenario
>>>
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