https://github.com/mbullington/turf-diameter

An unofficial Turf function for calculating the polygon diameter of a Feature.
https://github.com/mbullington/turf-diameter

algorithm geojson javascript turfjs

Last synced: about 1 month ago
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An unofficial Turf function for calculating the polygon diameter of a Feature.

• Host: GitHub
• URL: https://github.com/mbullington/turf-diameter
• Owner: mbullington
• License: other
• Created: 2019-06-07T05:23:07.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2023-01-03T23:36:13.000Z (almost 2 years ago)
• Last Synced: 2024-05-09T14:42:42.781Z (6 months ago)
• Topics: algorithm, geojson, javascript, turfjs
• Language: JavaScript
• Size: 1.61 MB
• Stars: 1
• Watchers: 2
• Forks: 0
• Open Issues: 16
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE.md

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README

        
# turf-diameter

An unofficial Turf module for calculating the [polygon diameter](http://mathworld.wolfram.com/PolygonDiameter.html) of

a Feature or FeatureCollection.

## API

#### Table of Contents

-   [dtheta](#dtheta)

    -   [Parameters](#parameters)

-   [diameter](#diameter)

    -   [Parameters](#parameters-1)

    -   [Examples](#examples)

### dtheta

Returns the counter-clockwise angle between

`{ coords[a], coords[a + 1] }` to `{ coords[b], coords[b + 1] }`

#### Parameters

-   `coords` **[Array](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array)<\[[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number), [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)]>** List of GeoJSON coordinates

-   `a` **[Number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** starting index of the first ray

-   `b` **[Number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** starting index of the second ray

Returns **[Number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** counter-clockwise angle between 0 and `2 * pi`

### diameter

Takes a [Feature](Feature) or [FeatureCollection](FeatureCollection) and returns the

[polygon diameter](http://mathworld.wolfram.com/PolygonDiameter.html).

Internally, this uses the rotating calipers method and pseudocode

described [here](https://www.tvhoang.com/articles/2018/12/rotating-calipers).

The concepts from the article are based off of the following paper:

Shamos, Michael (1978). "Computational Geometry" (PDF). Yale University. pp. 76–81.

The rotating calipers method requires a convex hull so we use mapbox's concaveman,

which runs in `O(n * log n)` time as stated [here](https://github.com/mapbox/concaveman).

The algorithm in the paper runs in about O(n) time, making this entire algorithm

run in `O(n)` + `O(n * log n)` = `O(n * log n)` time.

#### Parameters

-   `geojson` **GeoJSON** input Feature or FeatureCollection

#### Examples

```javascript

const points = turf.featureCollection([

  turf.point([10.195312, 43.755225]),

  turf.point([10.404052, 43.8424511]),

  turf.point([10.579833, 43.659924]),

  turf.point([10.360107, 43.516688]),

  turf.point([10.14038, 43.588348]),

  turf.point([10.195312, 43.755225])

]);

const len = diameter(points);

```

Returns **[Number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** the polygon diameter of the GeoJSON