SimplePolyIntersect.jl

The small module SimplePolyIntersect.jl provides two methods,

• polyintersection(poly1, poly2; open_out)
• polyintersects(poly1, poly2)

This amounts to an interface to the intersection and intersects functions of LibGEOS.jl.

Usage

Add and include the file SimplePolyIntersect.jl to your project. Each of poly1 and poly2 should be given as $N \times 2$ matrices of points or a vector of 2-d points. The polygon can be closed (i.e. the last point is repeat of the first) or open. The output is a vector of matrices of the intersection polygon if it exists, and false otherwise.

p1 = [0 0 ; 0 1 ; 1 1 ; 1 0 ]; # a square
p2 = p1 .+ 0.5; # the same square shifted up and right by 0.5
p3 = p1 .+ 10; # a very distant square

polyintersection(p1, p2)[1]

"""
5×2 Matrix{Float64}:
 1.0  1.0
 1.0  0.5
 0.5  0.5
 0.5  1.0
 1.0  1.0
"""

polyintersection(p1, p3)

"""
false
"""

Note that the default of polyinersection is to return vertices of the intersection "closed;" repeating the first vertex at the end. This can be toggled with the named argument open_out = true.

If you just want to know whether poly1 and poly2 intersect, polyintersects(poly1, poly2) can be faster.

using BenchmarkTools

@btime polyintersection(p1, p3)

"""
  5.208 μs (76 allocations: 3.53 KiB)
false
"""

@btime polyintersects(p1, p3)

"""
  4.726 μs (66 allocations: 3.09 KiB)
false
"""

Demo

Add PlotlyJS if you don't already have it installed.

include("demo/demo.jl")

The red and blue polygons are the ones we wish to intersect.

We can then see that there are three polygons disconnected from each other that make up the intersection.