Point is inside polygon

Algorithm to determine whether a point is inside a polygon

Getting started:

Copy the pointIsInsidePolygon function code from point-is-inside-polygon.js and include it in your code.

Usage:

const point = {x: 100, y: 100};
const polygon = [
	{x: 20, y: 125},
	{x: 12, y: 100},
	{x: 75, y: 30}
];
const position = pointIsInsidePolygon(point, polygon);

Arguments:

1. point: An object with 2 keys:

   • x: X-coordinate of the point.
   • y: Y-coordinate of the point.

2. polygon: An array of the polygon's points. Each point is an object with 2 keys:

   • x: X-coordinate of the point.
   • y: Y-coordinate of the point.

Return value:

• If the first argument point was not provided correctly it will return this error object:

{error: 'First argument should be a point with (x & y) coordinates'}

• If the second argument polygon was not provided correctly it will return this error object:

{error: 'Second argument should be an array of at least 3 points with (x & y) coordinates'}

• If both arguments were provided correctly it will return an object with 3 keys:

  1. isInside (boolean): true if the point was inside the polygon, and false if not.
  2. isOutside (boolean): true if the point was outside the polygon, and false if not.
  3. isOnBorder (boolean): true if the point was on the border of the polygon, and false if not.

{isInside: boolean, isOutside: boolean, isOnBorder: boolean}

Explanation:

The relative position of the point to the polygon will be determined based on number of intersections between the polygon & the horizontal line drawn starting from the point toward increasing the x-axis.

• If number of intersections was odd, then the point is inside the polygon.

• If number of intersections was even, then the point is outside the polygon.

Clone the repository and run index.html in your browser to test it.

Author:

Yaser Somaf https://github.com/yasershomaf yasershomaf@gmail.com