Inpolygon usage

New to Julia
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1

How can we generate following Octave codes in Julia with GeometricalPredicates package

xv = [ 0.05840, 0.48375, 0.69356, 1.47478, 1.32158, ...
        1.94545, 2.16477, 1.87639, 1.18218, 0.27615, ...
        0.05840 ];
 yv = [ 0.60628, 0.04728, 0.50000, 0.50000, 0.02015, ...
        0.18161, 0.78850, 1.13589, 1.33781, 1.04650, ...
        0.60628 ];
 xa = [0:0.1:2.3];
 ya = [0:0.1:1.4];
 [x,y] = meshgrid (xa, ya);
 [inn,on] = inpolygon (x, y, xv, yv);
 inside = inn & ! on;

What is the correct usage of inpolygon function of GeometricalPredicates package in this case?

2

GeometricalPredicates is not very convenient to use, since it requires all input coordinates to be in the range [1,2]. Also, it seems to only support inpolygon for convex polygons.
If you don’t need the very high precision near the edges that GeometricalPredicates seems to be trying to achieve, I recommend using Luxor instead:

using Luxor

xv = [ 0.05840, 0.48375, 0.69356, 1.47478, 1.32158, 
        1.94545, 2.16477, 1.87639, 1.18218, 0.27615, 
        0.05840 ]
yv = [ 0.60628, 0.04728, 0.50000, 0.50000, 0.02015, 
        0.18161, 0.78850, 1.13589, 1.33781, 1.04650, 
        0.60628 ]

xa = 0:0.1:2.3
ya = 0:0.1:1.4

polygon = Point.(xv,yv)
points = vec(Point.(xa',ya))

inside = [isinside(p, polygon; allowonedge=true) for p in points]

using Plots
plot(Tuple.(polygon), legend=false)
scatter!(Tuple.(points), marker_z=inside)

tmp

6 Likes
3

This is very good. Thank you.

4

If you want something more lightweight and flexible you can try PolygonOps, inpolygon function.

using PolygonOps
using StaticArrays

xv = [ 0.05840, 0.48375, 0.69356, 1.47478, 1.32158, 
        1.94545, 2.16477, 1.87639, 1.18218, 0.27615, 
        0.05840 ]
yv = [ 0.60628, 0.04728, 0.50000, 0.50000, 0.02015, 
        0.18161, 0.78850, 1.13589, 1.33781, 1.04650, 
        0.60628 ]

xa = 0:0.1:2.3
ya = 0:0.1:1.4

polygon = SVector.(xv,yv)
points = vec(SVector.(xa',ya))

inside = [inpolygon(p, polygon; in=true, on=false, out=false) for p in points]

using Plots
plot(Tuple.(polygon), legend=false)
scatter!(Tuple.(points), marker_z=inside)
7 Likes
5

Thank you. This is good.

6

After some experiments, I have found that PolygonOps is better suited for me. Thanks again.

7

@sjkelly’s example should be in the docs :slight_smile:
https://juliageometry.github.io/PolygonOps.jl/stable/

8

Good idea! Added :slight_smile: