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)