polygon-utils
v1.1.0
Published
Library for calculation of polygon centroid and bounding box area.
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polygon-utils
Library for calculation of polygon centroid and bounding box area.
Motive for this tiny library was:
- There wasn't similar libraries in TypeScript.
- I think it's very easy-to-understand.
- It's modular so people can instead of importing this just copy and paste the code and that's fine! I'd much prefer that too. Every extra library adds bloat and is a security risk.
The algorithm for the centroid was transformed from this C++ version https://stackoverflow.com/questions/2792443/finding-the-centroid-of-a-polygon to TypeScript. And that is translated from its mathematical formula https://en.wikipedia.org/wiki/Centroid#Centroid_of_a_polygon.
NOTE: this doesn't take into consideration Earth's curvature like eg. this library does https://github.com/mapbox/geojson-area. But if very slight inaccuracies don't bother you, this is a good estimate nonetheless.
How to install
npm i polygon-utils
How to develop locally
Requires: Node.js >= 8.
- Clone this repo & run
npm i
. - Start TypeScript compiler in watch mode:
npm run ts:watch
. All changes should update automatically.
To test as a local dependency:
- In the root of this project run:
npm link
. This will make it available as a global dependency for any local npm projects. - In a project where you'd like to use it as a dependency run:
npm link polygon-utils
. Now you can use it inside the project like a normal dependency:import { centroid } from 'polygon-utils'
.
API
/**
* Calculates the centroid of a polygon from a list of [x,y] coordinates.
* @param vertices List of [x,y] coordinates.
* @return Centroid as [x,y] coordinates eg. [23.5960126585797, 63.19228972849327].
*/
/**
* Calculates a weighted average of polygons' centroids.
* A reasonable estimate for the centroid instead of using the first centroid of the list.
* @param polygons List of polygons.
* @return Centroid as [x,y] coordinates eg. [23.5960126585797, 63.19228972849327].
*/
export function centroidMultiPolygon(polygons: number[][][][]) : [number, number]
/**
* Calculates the bounding box area of a polygon.
* @param vertices List of [x,y] coordinates.
* @return Area as floating number eg. 0.21966561631020753.
*/
export function boundingBoxArea(vertices: number[][]) : number
/**
* Convenience method to compute the polygon area for a MultiPolygon shape.
* @param polygons List of polygons.
* @return Area as a floating number eg. 5.20340858889998636.
*/
export function boundingBoxAreaMultiPolygon(polygons: number[][][][]) : number