@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 two or more polygons and returns a combined polygon. If the input polygons are not contiguous, this function returns a MultiPolygon feature.

Parameters

• A ...Feature<Polygon> polygon to combine

Examples

var 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"});
var poly2 = turf.polygon([[
    [-82.560024, 35.585153],
    [-82.560024, 35.602602],
    [-82.52964, 35.602602],
    [-82.52964, 35.585153],
    [-82.560024, 35.585153]
]], {"fill": "#00f"});

var union = turf.union(poly1, poly2);

//addToMap
var addToMap = [poly1, poly2, union];

Returns Feature<(Polygon | MultiPolygon)> a combined Polygon or MultiPolygon feature

---

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 module individually:

$ npm install @turf/union

Or install the Turf module that includes it as a function:

$ npm install @turf/turf

Changelog

5.0.0 🎉

⭐️ Major Updates

• TurfJS now supports ES Modules (Related PR's)
• Optional parameters are now defined as an Object.

🚀 New Modules

[@turf/voronoi][voronoi]

Takes a FeatureCollection of points, and a bounding box, and returns a FeatureCollection of Voronoi polygons. (PR https://github.com/Turfjs/turf/pull/1043 - Author @stevage)

[@turf/shortest-path][shortest-path]

Returns the shortest path from start to end without colliding with any feature in obstacles (PR https://github.com/Turfjs/turf/pull/956 - Author @stebogit)

[@turf/boolean-parallel][boolean-parallel]

Boolean-Parallel returns True if each segment of line1 is parallel to the correspondent segment of line2 (PR https://github.com/Turfjs/turf/pull/941 - Author @stebogit)

[@turf/nearest-point-on-line][nearest-point-on-line]

Takes a {@link Point} and a {@link LineString} and calculates the closest Point on the (Multi)LineString. (PR https://github.com/Turfjs/turf/pull/939 - Author @stebogit)

🏅 New Features/Enhancements

• Updates [@turf/unkink-polygon][unkink-polygon] testing & added flattenEach instead of using flatten. (PR https://github.com/Turfjs/turf/pull/889)

• Add multi-geomtry support to @turf/line-split (PR https://github.com/Turfjs/turf/pull/1078)

• Improve @turf/meta lineEach method to provide properties, id and bbox (PR https://github.com/Turfjs/turf/pull/1010)

🐛 Bug Fixes

• Fixes @turf/helpers earth radius variable (PR https://github.com/Turfjs/turf/pull/1012)

• Fixes @turf/polygon-tangents bug (PR https://github.com/Turfjs/turf/pull/1058)

• Fixes @turf/line-chunk bug when the number of segments is integer (PR https://github.com/Turfjs/turf/pull/1046)

• Fixes segmentEach and segmentReduce methods in @turf/meta to ensure something is returned (PR https://github.com/Turfjs/turf/pull/968)

⚠️ Breaking Change

• Optional parameters are now defined as an Object:

Before

var from = [-75.343, 39.984];
var to = [-75.534, 39.123];
var units = 'miles';
var distance = turf.distance(from, to, units);

After

var from = [-75.343, 39.984];
var to = [-75.534, 39.123];
var options = {units: 'miles'};
var distance = turf.distance(from, to, options);

• Reworked @turf/random PR https://github.com/Turfjs/turf/issues/994
• Deprecate @turf/idw Issue https://github.com/Turfjs/turf/issues/887
• Reworked Grid modules @turf/point-grid/hex/square/triangle PR https://github.com/Turfjs/turf/pull/1029
• Renamed Modules/Methods
  • [x] @turf/inside => @turf/boolean-point-in-polygon https://github.com/Turfjs/turf/issues/860#issuecomment-317216235
  • [x] @turf/within => @turf/points-within-polygon https://github.com/Turfjs/turf/issues/860#issuecomment-317216235
  • [x] @turf/bezier => @turf/bezier-spline Issue https://github.com/Turfjs/turf/issues/661
  • [x] @turf/nearest => @turf/nearest-point https://github.com/Turfjs/turf/pull/858#issuecomment-317197295
  • [x] @turf/point-on-line => @turf/nearest-point-on-line https://github.com/Turfjs/turf/pull/858#issuecomment-317197295
  • [x] @turf/lineDistance => @turf/length https://github.com/Turfjs/turf/issues/860#issuecomment-317229869
  • [x] @turf/helpers
    • [x] radians2degrees => radiansToDegrees
    • [x] degrees2radians => degreesToRadians
    • [x] distanceToDegrees => lengthToDegrees
    • [x] distanceToRadians => lengthToRadians
    • [x] radiansToDistance => radiansToLength
    • [x] bearingToAngle => bearingToAzimuth
    • [x] convertDistance => convertLength