@turf/union

What is @turf/union?

@turf/union is a part of the Turf.js library, which is a powerful geospatial analysis library written in JavaScript. The @turf/union package specifically allows you to perform union operations on GeoJSON polygons, merging multiple polygons into a single polygon.

What are @turf/union's main functionalities?

Union of Two Polygons

This feature allows you to merge two GeoJSON polygons into a single polygon. The code sample demonstrates how to create two polygons and then merge them using the `turf.union` function.

const turf = require('@turf/turf');

const polygon1 = turf.polygon([[
  [-82.574787, 35.594087],
  [-82.574787, 35.615581],
  [-82.545261, 35.615581],
  [-82.545261, 35.594087],
  [-82.574787, 35.594087]
]]);

const polygon2 = turf.polygon([[
  [-82.560024, 35.585153],
  [-82.560024, 35.602602],
  [-82.52964, 35.602602],
  [-82.52964, 35.585153],
  [-82.560024, 35.585153]
]]);

const union = turf.union(polygon1, polygon2);
console.log(JSON.stringify(union));

Union of Multiple Polygons

This feature allows you to merge multiple GeoJSON polygons into a single polygon. The code sample demonstrates how to create three polygons and then merge them sequentially using the `turf.union` function.

const turf = require('@turf/turf');

const polygon1 = turf.polygon([[
  [-82.574787, 35.594087],
  [-82.574787, 35.615581],
  [-82.545261, 35.615581],
  [-82.545261, 35.594087],
  [-82.574787, 35.594087]
]]);

const polygon2 = turf.polygon([[
  [-82.560024, 35.585153],
  [-82.560024, 35.602602],
  [-82.52964, 35.602602],
  [-82.52964, 35.585153],
  [-82.560024, 35.585153]
]]);

const polygon3 = turf.polygon([[
  [-82.554024, 35.580153],
  [-82.554024, 35.595602],
  [-82.52464, 35.595602],
  [-82.52464, 35.580153],
  [-82.554024, 35.580153]
]]);

let union = turf.union(polygon1, polygon2);
union = turf.union(union, polygon3);
console.log(JSON.stringify(union));

Other packages similar to @turf/union

jsts

JSTS is a JavaScript library of spatial predicates and functions for processing geometry. It is a port of the well-known Java Topology Suite (JTS). JSTS provides a wide range of geometric operations, including union, intersection, and difference. Compared to @turf/union, JSTS offers a more comprehensive set of geometric operations but may be more complex to use.

martinez-polygon-clipping

Martinez Polygon Clipping is a library for performing boolean operations on polygons, such as union, intersection, and difference. It is known for its performance and accuracy. Compared to @turf/union, Martinez Polygon Clipping is more focused on boolean operations and may offer better performance for these specific tasks.

README

@turf/union

union

Takes a collection of input polygons and returns a combined polygon. If the input polygons are not contiguous, this function returns a multi-polygon feature.

Parameters

• features FeatureCollection<(Polygon | MultiPolygon)> input polygon features

• options Object Optional Parameters (optional, default {})

  • options.properties GeoJsonProperties properties to assign to output feature (optional, default {})

Examples

const poly1 = turf.polygon(
  [
    [
      [-82.574787, 35.594087],
      [-82.574787, 35.615581],
      [-82.545261, 35.615581],
      [-82.545261, 35.594087],
      [-82.574787, 35.594087],
    ],
  ],
  { fill: "#0f0" }
);

const poly2 = turf.polygon(
  [
    [
      [-82.560024, 35.585153],
      [-82.560024, 35.602602],
      [-82.52964, 35.602602],
      [-82.52964, 35.585153],
      [-82.560024, 35.585153],
    ],
  ],
);

const union = turf.union(turf.featureCollection([poly1, poly2]));

//addToMap
const addToMap = { poly1, poly2, union };

poly1.properties.fill = "#0f0";
poly2.properties.fill = "#00f";
union.properties.stroke = "red";
union.properties["stroke-width"] = 4;
union.properties.fill = "transparent";

Returns (Feature<(Polygon | MultiPolygon)> | null) a combined polygon or multi-polygon feature, or null if there were no input polygons to combine

---

This module is part of the Turfjs project, an open source module collection dedicated to geographic algorithms. It is maintained in the Turfjs/turf repository, where you can create PRs and issues.

Installation

Install this single module individually:

$ npm install @turf/union

Or install the all-encompassing @turf/turf module that includes all modules as functions:

$ npm install @turf/turf