pip

🎯 Point in Polygon - Go

Detect if a point (X, Y) is within a given polygon (Set of X, Ys) .

Usage

import pip

// Polygons are self closing (i.e. you don't need to add first point at end)
rectangle := pip.Polygon{
  Points : []pip.Point {
    pip.Point{X : 1.0, Y : 1.0},
    pip.Point{X : 1.0, Y : 2.0},
    pip.Point{X : 2.0, Y : 2.0},
    pip.Point{X : 2.0, Y : 1.0},
  },
}

pt1 := pip.Point{X : 1.1,  Y : 1.1}

pip.PointInPolygon(pt1, rectangle) // Test - Should return true

Caveats

• Currently no support for holes although this should be easy to account for if the hole is tested as a separate polygon.
• Currently no support for points that reside on edges (returns outside, i.e. false).
• Beware of roundoff errors
• The direction that you list the vertices (clockwise or counterclockwise) does not matter.

Credit

Based on the example code given in this article by W. Randolph Franklin. The method is named PNPOLY.

License

MIT License Original C code : Copyright (c) 1970-2003, Wm. Randolph Franklin Modified Go code: Copyright 2016 James Milner