> -----Oorspronkelijk bericht-----
> Van: [email protected] [mailto:programming-
> [email protected]] Namens Dan Bron
> Verzonden: vrijdag 16 april 2010 17:02
> Aan: 'Programming forum'
> Onderwerp: [Jprogramming] Polygon containment
>
> Guys,
>
> I need to check whether a point falls within an arbitrary polygon.
>
(...)
I prefer to solve this problem, assuming the polygon is convex.
pip=: 4 : 0
NB. point in polygon, x is point
NB. y is polygon with 2 -: {:$y, such that _2[(,{.)y are edges
NB. 1 if in polygon, 0 if on edge or vertex, _1 if outside
E=. _1 ,.~ (%."(2) 2[\(,{.)y) +/ . * 1 1
s=. * E +/ . *"(1) _2|.y ,. 1
t=. * E +/ . *"(1) x , 1
<: (+: s -: t) + (0 e. t)
)
V=: _1 _1, 1 _1, 2 2 ,: _1 1
(3 4, _1 0 ,: 0 0) pip"1 _ V
_1 0 1
Some efficiency improvements may be possible.
R.E. Boss
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