Polygonize

Polygonizes a set of Geometrys which contain linework that represents the edges of a planar graph. It's basically an implementation of GEOS's Polygonizer.

Although, the algorithm is the same as GEOS, it isn't a literal transcription of the C++ source code. It was rewriten in order to get a more javascript like code.

JSDoc

/**
 * Polygonizes {@link LineString|(Multi)LineString(s)} into {@link Polygons}.
 *
 * Implementation of GEOSPolygonize function (`geos::operation::polygonize::Polygonizer`).
 *
 * Polygonizes a set of lines that represents edges in a planar graph. Edges must be correctly
 * noded, i.e., they must only meet at their endpoints.
 *
 * The implementation correctly handles:
 *
 * - Dangles: edges which have one or both ends which are not incident on another edge endpoint.
 * - Cut Edges (bridges): edges that are connected at both ends but which do not form part of a polygon.
 *
 * @name polygonize
 * @param {FeatureCollection|Geometry|Feature<LineString|MultiLineString>} geoJson Lines in order to polygonize
 * @returns {FeatureCollection<Polygon>} Polygons created
 * @throws {Error} if geoJson is invalid.
 */

Example

This example is the test found in test/in/complex.geojson.

const polygonize = require('polygonize'),
    fs = require('fs'),
    input = JSON.parse(fs.readFileSync('./test/in/complex.geojson'));
 
console.log(JSON.stringify(polygonize(input)));

The input as GeoJson LineString:

Turned into polygons:

Documentation

Polygonizes (Multi)LineString(s) into Polygons.

Implementation of GEOSPolygonize function (geos::operation::polygonize::Polygonizer).

Polygonizes a set of lines that represents edges in a planar graph. Edges must be correctly noded, i.e., they must only meet at their endpoints.

The implementation correctly handles:

• Dangles: edges which have one or both ends which are not incident on another edge endpoint.
• Cut Edges (bridges): edges that are connected at both ends but which do not form part of a polygon.

Parameters

• geojson (FeatureCollection | Geometry | Feature<(LineString | MultiLineString)>) Lines in order to polygonize

• Throws Error if geoJson is invalid.

Returns FeatureCollection<Polygon> Polygons created

Installation

Install this module individually:

$ npm install polygonize