determine if a point is inside a polygon with a ray intersection counting algorithm

Usage no npm install needed!

<script type="module">
  import pointInPolygon from 'https://cdn.skypack.dev/point-in-polygon';



Determine if a point is inside of a polygon.

This module casts a semi-infinite ray from the inquiry point and counts intersections, based on this algorithm.

If you need a numerically robust solution and are willing to trade some performance for it, use robust-point-in-polygon.


var pointInPolygon = require('point-in-polygon');
var polygon = [ [ 1, 1 ], [ 1, 2 ], [ 2, 2 ], [ 2, 1 ] ];

console.log(pointInPolygon([ 1.5, 1.5 ], polygon)); // true
console.log(pointInPolygon([ 4.9, 1.2 ], polygon)); // false
console.log(pointInPolygon([ 1.8, 1.1 ], polygon)); // true


var pointInPolygon = require('point-in-polygon')
var pointInPolygonFlat = require('point-in-polygon/flat')
var pointInPolygonNested = require('point-in-polygon/nested')

pointInPolygon(point, polygon, start=0, end=polygon.length)

Return whether point is contained in polygon.

  • point should be a 2-item array of coordinates
  • polygon should be an array of 2-item arrays of coordinates or a flat array of coordinates
  • start is an offset into polygon. default 0
  • end is an offset into polygon. default polygon.length

The flat or nested is detected automatically. Or you can use the specific methods if you want to skip the check.


npm install point-in-polygon