# @turf/concave

# concave

Takes a set of [points](http://geojson.org/geojson-spec.html#point) and returns a concave hull Polygon or MultiPolygon.
Internally, this uses [turf-tin](https://github.com/Turfjs/turf-tin) to generate geometries.

**Parameters**

-   `points` **[FeatureCollection](http://geojson.org/geojson-spec.html#feature-collection-objects)<[Point](http://geojson.org/geojson-spec.html#point)>** input points
-   `maxEdge` **[number](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number)** the length (in 'units') of an edge necessary for part of the hull to become concave
-   `units` **\[[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)]** can be degrees, radians, miles, or kilometers (optional, default `kilometers`)

**Examples**

```javascript
var points = turf.featureCollection([
  turf.point([-63.601226, 44.642643]),
  turf.point([-63.591442, 44.651436]),
  turf.point([-63.580799, 44.648749]),
  turf.point([-63.573589, 44.641788]),
  turf.point([-63.587665, 44.64533]),
  turf.point([-63.595218, 44.64765])
]);

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

//addToMap
var addToMap = [points, hull]
```

-   Throws **[Error](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)** if maxEdge parameter is missing or unable to compute hull

Returns **[Feature](http://geojson.org/geojson-spec.html#feature-objects)<([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))>** a concave hull

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---

This module is part of the [Turfjs project](http://turfjs.org/), an open source
module collection dedicated to geographic algorithms. It is maintained in the
[Turfjs/turf](https://github.com/Turfjs/turf) repository, where you can create
PRs and issues.

### Installation

Install this module individually:

```sh
$ npm install @turf/concave
```

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

```sh
$ npm install @turf/turf
```