polygonize

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

/** 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. LineStrings must only have two coordinate
 * points.
 *
 * 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.
 *
 * @param {FeatureCollection<LineString>} geoJson - Lines in order to polygonize
 * @returns {FeatureCollection<Polygon>} - Polygons created
 */

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

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. LineStrings must only have two coordinate points.

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<LineString> Lines in order to polygonize

Returns FeatureCollection<Polygon> Polygons created

Installation

Install this module individually:

$ npm install polygonize