@turf/concave

What is @turf/concave?

@turf/concave is a module within the Turf.js library that allows you to generate concave hull polygons from a set of points. This can be useful for creating boundaries that more closely fit the shape of the input points compared to convex hulls.

What are @turf/concave's main functionalities?

Generate Concave Hull

This feature allows you to generate a concave hull polygon from a set of points. The `maxEdge` parameter controls the maximum length of an edge in the hull, which influences the 'concaveness' of the resulting polygon.

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

const points = turf.featureCollection([
  turf.point([10, 10]),
  turf.point([20, 20]),
  turf.point([30, 10]),
  turf.point([40, 40]),
  turf.point([50, 30])
]);

const concaveHull = turf.concave(points, {maxEdge: 25});

console.log(JSON.stringify(concaveHull));

Other packages similar to @turf/concave

hull.js

Hull.js is a JavaScript library for computing the convex hull of a set of 2D points. Unlike @turf/concave, which generates concave hulls, hull.js focuses on convex hulls, which are simpler and faster to compute but may not fit the shape of the input points as closely.

concaveman

Concaveman is a very fast 2D concave hull algorithm. It is similar to @turf/concave in that it generates concave hulls, but it is optimized for performance and simplicity. It may not offer as many configuration options as @turf/concave.

README

@turf/concave

concave

Takes a set of points and returns a concave hull polygon.

Internally, this uses turf-tin to generate geometries.

Parameters

• points FeatureCollection<Point> input points
• maxEdge number the size of an edge necessary for part of the hull to become concave (in miles)
• units [string] can be degrees, radians, miles, or kilometers (optional, default kilometers)

Examples

var points = {
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Point",
        "coordinates": [-63.601226, 44.642643]
      }
    }, {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Point",
        "coordinates": [-63.591442, 44.651436]
      }
    }, {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Point",
        "coordinates": [-63.580799, 44.648749]
      }
    }, {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Point",
        "coordinates": [-63.573589, 44.641788]
      }
    }, {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Point",
        "coordinates": [-63.587665, 44.64533]
      }
    }, {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Point",
        "coordinates": [-63.595218, 44.64765]
      }
    }
  ]
};

var hull = turf.concave(points, 1, 'miles');

var resultFeatures = points.features.concat(hull);
var result = {
  "type": "FeatureCollection",
  "features": resultFeatures
};

//=result

• Throws Error if maxEdge parameter is missing or unable to compute hull

Returns Feature<Polygon> a concave hull

---

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/concave

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

$ npm install @turf/turf