AlainGourves / convex-hull

Javascript implementation of the Graham Scan algorithm to find the convex hull of a set of points

Convex Hull

This library computes the convex hull of a set of points.

It uses the Graham scan algorithm.

References:

• Wikipedia
• Algorithm Archive
• This code is largely inspired by this Geeksforgeeks's post.

Installation

Copy ./lib/points.js and ./lib/convexHull.js files.

Point are objects with x and y properties representing their coordinates.

Usage

import ConvexHull from './lib/convexHull.js';

let points =[
    new Point(17, 16),
    new Point(35, 4),
    new Point(26, 45),
    new Point(43, 25),
    new Point(65, 21),
];

let hull = new ConvexHull(points);
console.log(hull.getPoints());

Result :

[
  Point { x: 26, y: 45 },
  Point { x: 17, y: 16 },
  Point { x: 35, y: 4 },
  Point { x: 65, y: 21 }
]

Notes:

• The resulting points are ordered starting from the lowest left, then following the envelope clockwise.
• The path is not closed (the last point is not the same as the first).

Ideas

• Optimize the code by interior elimination (or quadrilateral culling) : find the farthest points in the NW, NE, SE & SW directions and eliminate the points inside the quadrilateral they defined (as these points cannot be on the hull).
• Implement other algorithms, like Quickhull.