polyclip-ts

Apply boolean polygon clipping operations (intersection, union, difference, xor) to your Polygons & MultiPolygons.

Installing

If you use npm, npm install polyclip-ts. You can also download the latest release on GitHub. For vanilla HTML in modern browsers, import polyclip-ts from Skypack:

<script type="module">
import * as polyclip from "https://cdn.skypack.dev/polyclip-ts";

polyclip.intersection(…)
</script>

For legacy environments, you can load polyclip-ts’s UMD bundle from an npm-based CDN such as jsDelivr; a polyclip global is exported:

<script src="https://cdn.jsdelivr.net/npm/polyclip-ts/dist/polyclip-ts.umd.min.js"></script>
<script>
polyclip.intersection(…)
</script>

Quickstart

import * as polyclip from "polyclip-ts"

const poly1 = [[[0,0],[2,0],[0,2],[0,0]]]
const poly2 = [[[-1,0],[1,0],[0,1],[-1,0]]]

polyclip.union       (poly1, poly2 /* , poly3, ... */)
polyclip.intersection(poly1, poly2 /* , poly3, ... */)
polyclip.xor         (poly1, poly2 /* , poly3, ... */)
polyclip.difference  (poly1, poly2 /* , poly3, ... */)

API

/* All functions take one or more [multi]polygon(s) as input */

polyclip.union       (geom, ...moreGeoms)
polyclip.intersection(geom, ...moreGeoms)
polyclip.xor         (geom, ...moreGeoms)

/* The moreGeoms will be subtracted from the geom */
polyclip.difference  (geom, ...moreGeoms)

Input

Each positional argument (geom) may be either a Polygon or a MultiPolygon. The GeoJSON spec is followed, with the following notes/modifications:

MultiPolygons may contain touching or overlapping Polygons.
rings are not required to be self-closing.
rings may contain repeated points, which are ignored.
rings may be self-touching and/or self-crossing. Self-crossing rings will be interpreted using the non-zero rule.
winding order of rings does not matter.
inner rings may extend outside their outer ring. The portion of inner rings outside their outer ring is dropped.
inner rings may touch or overlap each other.

Output

For non-empty results, output will always be a MultiPolygon containing one or more non-overlapping, non-edge-sharing Polygons. The GeoJSON spec is followed, with the following notes/modifications:

outer rings will be wound counter-clockwise, and inner rings clockwise.
inner rings will not extend outside their outer ring.
rings will not overlap, nor share an edge with each other.
rings will be self-closing.
rings will not contain repeated points.
rings will not contain superfluous points (intermediate points along a straight line).
rings will not be self-touching nor self-crossing.
rings may touch each other, but may not cross each other.

In the event that the result of the operation is the empty set, output will be a MultiPolygon with no Polygons: [].

Correctness

Run: npm test

The tests are broken up into unit tests and end-to-end tests. The end-to-end tests are organized as GeoJSON files, to make them easy to visualize thanks to GitHub's helpful rendering of GeoJSON files. Browse those tests here.

Performance

The Martinez-Rueda-Feito polygon clipping algorithm is used to compute the result in O((n+k)*log(n)) time, where n is the total number of edges in all polygons involved and k is the number of intersections between edges.

Authors

Based on

A simple algorithm for Boolean operations on polygons by Francisco Martinez, Antonio Jesus Rueda, Francisco Ramon Feito (2009)

luizbarboza / polyclip-ts

readme