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simplify-geojson-visvalingam

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[npm-url]: https://www.npmjs.com/package/simplify-geojson-visvalingam

Takes a [GeoJSON][1] object and returns a simplified version. Uses the [Visvalingam–Wyatt][2] algorithm with additional logic for stable simplification and preservation of common boundaries.

Install

``
npm i --save simplify-geojson-visvalingam
`

Parameters

* geojson [GeoJSON][1] object to be simplified, should extends [GeoJsonObject][6] in TypeScript
* options [Object][3] Optional parameters (optional, default {}), should be of type [SimplifyOptions][7] in TypeScript

* options.tolerance [number][4] simplification tolerance, the minimum Cartesian area of ​​a triangle formed by a point and its two neighbors to preserve that point (optional, default 0)
* options.fraction [number][4] the fraction of all points to be removed (optional, default 0)
* options.mutate [boolean][5] allows GeoJSON input to be mutated (optional, default true)

> tolerance and fraction can be used together to make the simplification satisfy both options, but if neither is provided, the geojson will remain unsimplified

Features and limitations

* Provides stable simplification and a better level of visual detail than the [Ramer–Douglas–Peucker][8] algorithm
* Will remove common points of different geometries simultaneously to preserve common boundaries
* Will leave valid empty Feature objects even if all their geometry will be removed, the GeoJSON structure will remain intact
* The start and end point of the LineString objects will never be removed

Usage

$3

`javascript
import simplify from 'simplify-geojson-visvalingam'

// CommonJS
// const simplify = require('simplify-geojson-visvalingam').default

const geojson = {
"type": "Polygon",
"coordinates": [
[
[-70.603637, -33.399918],
[-70.614624, -33.395332],
[-70.639343, -33.392466],
[-70.659942, -33.394759],
[-70.683975, -33.404504],
[-70.697021, -33.419406],
[-70.701141, -33.434306],
[-70.700454, -33.446339],
[-70.694274, -33.458369],
[-70.682601, -33.465816],
[-70.668869, -33.472117],
[-70.646209, -33.473835],
[-70.624923, -33.472117],
[-70.609817, -33.468107],
[-70.595397, -33.458369],
[-70.587158, -33.442901],
[-70.587158, -33.426283],
[-70.590591, -33.414248],
[-70.594711, -33.406224],
[-70.603637, -33.399918]
]
]
}
const options = {
tolerance: 0.00008, // remove all points that form a triangle with a smaller Cartesian area
}
const result = simplify(geojson, options)
`


$3


`typescript
import { type Polygon } from 'geojson'
import simplify, { type SimplifyOptions } from 'simplify-geojson-visvalingam'

const geojson: Polygon = {
"type": "Polygon",
"coordinates": [
[
[-70.603637, -33.399918],
[-70.614624, -33.395332],
[-70.639343, -33.392466],
[-70.659942, -33.394759],
[-70.683975, -33.404504],
[-70.697021, -33.419406],
[-70.701141, -33.434306],
[-70.700454, -33.446339],
[-70.694274, -33.458369],
[-70.682601, -33.465816],
[-70.668869, -33.472117],
[-70.646209, -33.473835],
[-70.624923, -33.472117],
[-70.609817, -33.468107],
[-70.595397, -33.458369],
[-70.587158, -33.442901],
[-70.587158, -33.426283],
[-70.590591, -33.414248],
[-70.594711, -33.406224],
[-70.603637, -33.399918]
]
]
}
const options: SimplifyOptions = {
fraction: 0.5, // remove 50% of all points
}
const result = simplify(geojson, options)
``

[1]: https://tools.ietf.org/html/rfc7946#section-3

[2]: https://en.wikipedia.org/wiki/Visvalingam%E2%80%93Whyatt_algorithm

[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object

[4]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number

[5]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean

[6]: https://www.npmjs.com/package/@types/geojson

[7]: https://github.com/iamaleko/simplify-geojson-visvalingam/blob/56aece32122cb38f2d1cfc2e23a2b366d1e8ae5b/src/index.ts#L15

[8]: https://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm